UBC Theses and Dissertations

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UBC Theses and Dissertations

A study on the use of ICP-OES for the determination of nonmetals in organic solution Hauser, Peter Christian 1984

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A STUDY ON THE USE OF ICP-OES FOR THE DETERMINATION OF NONMETALS IN ORGANIC SOLUTION by PETER CHRISTIAN HAUSER Chem. HTL. W i n t e r t h u r P o l y t e c h n i c 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES ( D e p a r t m e n t o f C h e m i s t r y ) We a c c e p t t h i s t h e s i s as c o n f o r m i n g to t h e rejj,u3_T"e^-_atandard THE UNIVERSITY OF B R I T I S H COLUMBIA November 1984 ® P e t e r C h r i s t i a n H a u s e r , 1984 _c -In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 requirements for an advanced degree at the University E-6 (3/81) ABSTRACT The a p p l i c a t i o n o f I n d u c t i v e l y C o u p l e d P l a s m a O p t i c a l E m i s s i o n S p e c t r o m e t r y ( I C P - O E S ) t o t h e d e t e r m i n a t i o n o f t o t a l o x y g e n , n i t r o g e n and s u l p h u r i n o r g a n i c s o l u t i o n has b e e n s t u d i e d . N e a r - i n f r a r e d e m i s s i o n l i n e s o f t h e t h r e e n o n m e t a l s have been used and d e t e c t i o n l i m i t s i n x y l e n e have been e s t a b l i s h e d . Oxygen was d e t e r m i n e d f o r t h e f i r s t t i m e by ICP-OES i n a n o n g a s e o u s s a m p l e . The c h a r a c t e r i s t i c s o f t h e i n d u c t i v e l y c o u p l e d p l a s m a when u s e d w i t h an o r g a n i c a e r o s o l h a v e been s t u d i e d w i t h r e s p e c t t o t h e c o m p l e t e n e s s o f a t o m i z a t i o n and p o t e n t i a l i n t e r f e r e n c e f r o m t h e c o m p l e x e x c i t a t i o n e n v i r o n m e n t . S p a t i a l l y r e s o l v e d a t o m i c and m o l e c u l a r e m i s s i o n p r o f i l e s have been c o l l e c t e d as p a r t of t h e s e i n v e s t i g a t i o n s . The n o n m e t a l e m i s s i o n i n t e n s i t i e s were f o u n d t o depend on t h e b o i l i n g p o i n t o f t h e c o m p o u n d s c o n t a i n i n g t h e n o n m e t a l b e c a u s e a r e d i s t r i b u t i o n e f f e c t i n t h e n e b u l i z e r chamber was l e a d i n g t o an e n r i c h m e n t o f v o l a t i l e s o l u t e s i n t h e a e r o s o l s t r e a m t o t h e p l a s m a . R e s p o n s e f a c t o r s f o r a s e r i e s of compounds have been d e t e r m i n e d . The u t i l i t y o f t h e m e t h o d was shown by e s t a b l i s h i n g w o r k i n g c u r v e s and by t e s t i n g c e r t i f i e d s t a n d a r d s f o r s u l p h u r . OR. MICHAEL BLADES CHEMISTRY DEPT. i i UNIV. OF BRITISH COLUMBIA TABLE OF CONTENTS PAGE ABSTRACT i i TABLE OF CONTENTS i i i LIS T OF TABLES v i LIST OF FIGURES v i i CHAPTER I I N T R O D U C T I O N 1 1.1 OBJECTIVE 1 1.2 THE INDUCTIVELY COUPLED PLASMA 3 1.3 APPLICATIONS TO ORGANIC SAMPLES AND NONMETALS 8 1.4 FUNDAMENTALS OF ORGANIC SAMPLE INTRODUCTION 11 1.4.1 AEROSOL PRODUCTION 12 1.4.2 TORCH 15 1.4.3 PLASMA 16 1.4.4 SPECTRUM 20 1.4.5 SUMMARY 21 i i i I I EXPERIMENTAL 23 2.1 INSTRUMENTATION 23 2.2 TORCH 27 2.3 ACQUISITION OF EMISSION PROFILES 29 I I I R E S U L T S AND D I S C U S S I O N 31 3.1 NEAR-IR OXYGEN, NITROGEN AND SULPHUR LINES 31 3.2 PHYSICAL APPEARANCE OF THE *XYLENE-PLASMA* 37 3.3 COMPLETENESS OF ATOMIZATION 39 3.3.1 EMISSION FROM DIATOMIC MOLECULES 41 3.3.2 E M I S S I O N P R O F I L E S 44 3.3.2.1 C 2 AND CN 47 3.3.2.2 C I AND S I 53 3.3.3 CONCLUSIONS 58 3.4 OPTIMIZATION 59 3.4.1 ENTRAINMENT OF AIR 59 3.4.2 EXCLUSION OF AIR 59 3.4.3 AMBIENT OXYGEN AND NITROGEN 64 3.4.4 OPERATING CONDITIONS AND VIEWING REGION 66 3.4.5 CONTROLLEED SAMPLE DELIVERY 71 3.4.6 CONCLUSIONS 71 i v 3.5 ANALYTICAL PERFORMANCE 74 3.5.1 RESPONSE FROM DIFFERENT COMPOUNDS 74 3.5.1.1 VOLATILE SOLUTES 74 3.5.1.2 NONVOLATILE SOLUTES 79 3.5.2 AMOUNTS OF AMBIENT OXYGEN AND NITROGEN 82 3.5.3 SIGNAL TO BACKGROUND RATIOS 82 3.5.4 DRIFTS 82 3.5.5 DETECTION LIMITS 84 3.5.6 WORKING CURVES 87 3.5.7 CERTIFIED OIL STANDARDS FOR SULPHUR 91 IV CONCLUSION 96 BIBLIOGRAPHY 99 v LIST OF TABLES PAGE I O r g a n i c Sample I n t r o d u c t i o n 11 I I D i s s o c i a t i o n and I o n i z a t i o n E n e r g i e s 40 I I I Ex pe r i ment a 1 C o n d i t i o n s f o r P r o f i l e s 46 IV V o l a t i l e S o l u t e s 75 V N o n v o l a t i l e S o l u t e s 80 VI D e t e c t i o n L i m i t s 86 V I I NBS Samples 91 V I I I NBS: D i l u t i o n s 92 IX NBS: S t a n d a r d A d d i t i o n s 93 X NBS: B a c k g r o u n d S h i f t s 94 v i L I S T OF FIGURES PAGE 1 B l o c k Diagram of an I C P - S p e c t r o m e t e r 5 2 The I n d u c t i v e l y C o u p l e d Plasma 7 3 B l o c k D i a g r a m o f t h e I n s t r u m e n t a t i o n 24 4 ICP T o r c h 28 5 Asymmetric A b e l I n v e r s i o n 30 6 E m i s s i o n S p e ctrum a t 777 nm (Oxygen) 33 7 E m i s s i o n S p e ctrum a t 865 nm ( N i t r o g e n ) 34 8 E m i s s i o n S p e ctrum a t 820 nm ( N i t r o g e n ) 35 9 E m i s s i o n S p e c t r a a t 920 nm ( S u l p h u r ) 36 10 The ICP when X y l e n e a s p i r a t e d 38 11 E m i s s i o n S p e ctrum a t 515 nm ( C 2 Swan Band) 42 12 E m i s s i o n S p e c t r u m a t 415 nm (CN V i o l e t B and) 43 13 E x c i t a t i o n T e m p e r a t u r e P l o t s , 45 14 C2 E m i s s i o n P r o f i l e s 48 15 CN E m i s s i o n P r o f i l e s (1) 49 16 CN E m i s s i o n P r o f i l e s (2) 50 17 CN E m i s s i o n P r o f i l e s (3) 51 18 CN E m i s s i o n P r o f i l e s / P y r i d i n e added 52 19 CI E m i s s i o n P r o f i l e s (1) 54 20 CI E m i s s i o n P r o f i l e s (2) 55 21 SI E m i s s i o n P r o f i l e s (1) 56 22 SI E m i s s i o n P r o f i l e s (2) 57 v i i 23 01 E m i s s i o n P r o f i l e s 60 24 S e a l i n g of T o r c h E x t e n s i o n ,...61 25 T o r c h E x t e n s i o n s 63 26 C 2 E m i s s i o n P r o f i l e s w i t h E x t e n s i o n 65 27 01 E m i s s i o n I n t e n s i t y v s . V i e w i n g H e i g h t 68 28 SI E m i s s i o n I n t e n s i t y v s . V i e w i n g H e i g h t 69 29 L a t e r a l SI E m i s s i o n P r o f i l e s 70 30 E m i s s i o n I n t e n s i t y v s . B o i l i n g P o i n t o f t h e S o l u t e 76 31 01 E m i s s i o n I n t e n s i t y v s . Time when r e c y c l e d 78 32 Working C u r v e s f o r Oxygen 89 33 W orking C u r v e s f o r S u l p h u r 90 v i i i CHAPTER I INTRODUCTION 1.1 OBJECTIVE The i n d u c t i v e l y c o u p l e d p l a s m a ( I C P ) h a s become v e r y p o p u l a r as an e x c i t a t i o n s o u r c e i n a n a l y t i c a l a t o m i c s p e c t r o s c o p y . I t i s w i d e l y u s e d f o r t h e a n a l y s i s o f g e o l o g i c a l , i n d u s t r i a l , b i o l o g i c a l a n d e n v i r o n m e n t a l s a m p l e s . The v a s t m a j o r i t y o f t h e s e a p p l i c a t i o n s i n v o l v e a q u e o u s s o l u t i o n s o f m e t a l s . I n p r i n c i p l e , i n d u c t i v e l y c o u p l e d p l a s m a o p t i c a l e m i s s i o n s p e c t r o s c o p y (ICP-OES) c o u l d a l s o be a s i m p l e and r a p i d m e t h o d f o r t h e d e t e r m i n a t i o n o f n o n m e t a l s i n o r g a n i c s o l u t i o n s . However, the d e v e l o p m e n t o f t h i s a p p l i c a t i o n h a s b e e n s l o w b e c a u s e o f p r o b l e m s e n c o u n t e r e d w i t h t h e i n t r o d u c t i o n o f o r g a n i c s o l v e n t s and t h e l a c k o f s t r o n g e m i s s i o n l i n e s f o r some n o n m e t a l s ( i n p a r t i c u l a r f o r t h e i m p o r t a n t e l e m e n t s oxygen, n i t r o g e n and s u l p h u r ) i n t h e u s u a l a n a l y t i c a l r e g i o n (200-700 nm) o f the s p e c t r u m . T h e p r o b l e m s a s s o c i a t e d w i t h o r g a n i c s o l v e n t i n t r o d u c t i o n have been d i v e r s e . Soot d e p o s i t s on t h e p l a s m a t o r c h a n d i n s t a b i l i t i e s o f t h e p l a s m a i t s e l f h a v e b e e n e n c o u n t e r e d . The o b s e r v a t i o n o f m o l e c u l a r e m i s s i o n h a s b r o u g h t t h e d e g r e e o f a t o m i z a t i o n i n t o q u e s t i o n a n d 1 n e b u l i z e r s h a v e n o t b e e n w e l l c h a r a c t e r i z e d f o r o r g a n i c s o l v e n t s . M o s t n o n m e t a l s o f g r o u p s V, VI and V I I h a v e t h e i r s e n s i t i v e r e s o n a n t e m i s s i o n l i n e s i n t h e v a c u u m - u l t r a v i o l e t r e g i o n ( 1 0 0 - 200 nm). The d e t e c t i o n o f w a v e l e n g t h s b e l o w about 200 nm r e q u i r e s e v a c u a t i o n (hence v a c u u m - u l t r a v i o l e t ) or p u r g i n g o f t h e o p t i c a l p a t h ( i n c l u d i n g t h e monochromator) to e l i m i n a t e a b s o r p t i o n by a t m o s p h e r i c oxygen. A l s o , l i g h t a b s o r p t i o n by q u a r t z becomes a p p r e c i a b l e below 200 nm. Most a n a l y t i c a l I C P - s p e c t r o m e t e r s can o p e r a t e s u c c e s s f u l l y down t o a b o u t 180 nm when p u r g e d , so s u l p h u r , w h i c h h a s s t r o n g r e s o n a n t l i n e s a t 180 nm, and p o s s i b l y n i t r o g e n w i t h l i n e s a t 170 nm c a n be d e t e r m i n e d on an i n s t r u m e n t w h i c h c a n be e v a c u a t e d o r p u r g e d . F o r t h e m e a s u r e m e n t o f t h e r e s o n a n t l i n e s o f o x y g e n ( 130 nm) a p p r o p r i a t e l y b l a z e d g r a t i n g s and s p e c i a l d e t e c t o r s a r e n e c e s s a r y . R e c e n t l y , a t o r c h f o r s t a b l e use w i t h o r g a n i c s o l v e n t s h a s b e e n d e v e l o p e d and t h e d i f f e r e n t a s p e c t s o f o r g a n i c a e r o s o l p r o d u c t i o n and i n t r o d u c t i o n i n t o t h e p l a s m a h a v e been d e s c r i b e d f a i r l y w e l l . A l s o , ICP e m i s s i o n l i n e s o f the n o n m e t a l s have been r e p o r t e d i n t h e f a r r e d t o n e a r - i n f r a r e d r e g i o n (700 - 950 nm) and a p p l i c a t i o n s w i t h g aseous sample i n t r o d u c t i o n h a v e b e e n d e s c r i b e d . T h i s s p e c t r a l r e g i o n i s not n o r m a l l y used f o r a n a l y t i c a l a t o m i c s p e c t r o s c o p y but i s e a s i l y a c c e s s i b l e f o r c o n v e n t i o n a l s p e c t r o m e t e r s . 2 T h i s t h e s i s p r e s e n t s an i n v e s t i g a t i o n i n t o t h e f e a s i b i l i t y of d e t e r m i n i n g n o n m e t a l s i n o r g a n i c l i q u i d s w i t h a n I C P - o p t i c a l e m i s s i o n s p e c t r o m e t e r e m p l o y i n g t h o s e near i n f r a r e d e m i s s i o n l i n e s . The t e s t m a t r i x c o n s i s t e d o f s o l u t i o n s o f o r g a n i c c o m p o u n d s c o n t a i n i n g 0, N o r S i n x y l e n e . The m e t h o d h a s p o t e n t i a l u t i l i t y i n t h e p e t r o l e u m i n d u s t r y , w h e r e m o n i t o r i n g o f s u l p h u r and n i t r o g e n i s c r u c i a l i n t h e r e f i n i n g p r o c e s s , b e c a u s e t h e s e e l e m e n t s a c t a s c a t a l y s t p o i s o n e r s . A n o t h e r p o t e n t i a l a p p l i c a t i o n i s 1 i q u i d - c h r o m a t o g r a p h y , w h e r e e l e m e n t s e l e c t i v e d e t e c t i o n w i t h ICP-OES had g a i n e d much a t t e n t i o n r e c e n t l y , but has not i n c l u d e d t h e s e t h r e e n o n m e t a l s . 1.2 THE INDUCTIVELY COUPLED PLASMA The f i r s t u s e o f an ICP as an e x c i t a t i o n s o u r c e f o r a t o m i c s p e c t r o s c o p y was r e p o r t e d i n d e p e n d e n t l y by G r e e n f i e l d [ 1 ] and F a s s e l [2] 20 y e a r s ago. S i n c e t h e n i t has become v e r y p o p u l a r b e c a u s e o f i t s g o od d e t e c t i o n l i m i t s , h i g h p r e c i s i o n , a c c u r a c y and v e r s a t i l i t y c o m p a r e d t o o l d e r s p e c t r o s c o p i c m e t h o d s l i k e dc a r c - and s p a r k - e m i s s i o n , a t o m i c a b s o r p t i o n and x - r a y - f l u o r e s c e n c e . O t h e r p l a s m a s o u r c e s have been d e v e l o p e d , t h e d i r e c t - c u r r e n t p l a s m a , th e m i c r o w a v e - i n d u c e d p l a s m a (MIP) and t h e c a p a c i t i v e l y - c o u p l e d p l a s m a (CMP), but t h e ICP has been most e x p l o i t e d . T h e b a s i c c o m p o n e n t s o f an I C P - o p t i c a l e m i s s i o n s p e c t r o m e t e r a r e shown i n F i g u r e 1. The r a d i o f r e q u e n c y g e n e r a t o r s u p p l i e s t h e e n e r g y n e c e s s a r y t o s u s t a i n t h e p l a s m a . The p l a s m a i t s e l f i s l o c a t e d i n t h e p l a s m a box, w h i c h a l s o c o n t a i n s t h e u n i t s f o r i n p u t power m a t c h i n g and c o n t r o l o f gas f l o w r a t e s . Samples a r e u s u a l l y i n t r o d u c e d as a e r o s o l s w h i c h a r e p r o d u c e d i n e i t h e r c o n c e n t r i c or c r o s s -f l o w p n e u m a t i c n e b u l i z e r s . The s p e c t r o m e t e r n o r m a l l y i s b a s e d on a g r a t i n g and r e a d o u t i s u s u a l l y a c h i e v e d w i t h a p h o t o m u l t i p l i e r tube (PMT). S c a n n i n g m o n o c h r o m a t o r s c o n t a i n one e x i t s l i t - PMT c o m b i n a t i o n , so t h a t o n l y one e l e m e n t c a n be d e t e r m i n e d a t a t i m e . A d a p t i o n t o t h e d e t e r m i n a t i o n o f a d i f f e r e n t e l e m e n t i s e a s i l y a c h i e v e d by r o t a t i n g t h e g r a t i n g t o r e a d a d i f f e r e n t w a v e l e n g t h . D i r e c t r e a d e r s c o n t a i n a number o f PMTs, e a c h r e a d i n g one f i x e d l i n e . The number o f PMTs c o r r e s p o n d s w i t h t h e number o f e l e m e n t s w h i c h c a n be d e t e r m i n e d s i m u l t a n e o u s l y . I t s f l e x i b i l i t y i s l i m i t e d , b e c a u s e th e PMTs have t o be r e p o s i t i o n e d each t i m e t h e d e t e r m i n a t i o n o f a new s e t o f e l e m e n t s i s r e q u i r e d . P h o t o d i o d e a r r a y s as d e t e c t o r s c a n be u s e d t o o b s e r v e a s m a l l s p e c t r a l window. T h i s a l l o w s , i n f a v o u r a b l e c a s e s , the s i m u l t a n e o u s d e t e r m i n a t i o n of a few e l e m e n t s w h i l e r e t a i n i n g t h e f l e x i b i l i t y of a s c a n n i n g monochromator. A l s o , b ecause a s p e c t r a l window not j u s t t h e i n t e n s i t y of t h e a n a l y t i c a l l i n e i s measured, changes i n c o n t i n u u m b a c k g r o u n d 4 Monochromator T Readout I C P Radiofrequency Generator 1 Sample Introduction i Sample F i g u r e 1 . B l o c k Diagram of an ICP s p e c t r o m e t e r . 5 i n t e n s i t y c a n be e a s i l y r e c o g n i z e d and c o r r e c t i o n s made. H o w e v e r , t h e s e d e t e c t o r s h a v e n o t y e t f o u n d c o m m e r c i a l a p p l i c a t i o n i n a t o m i c s p e c t r o s c o p y . A d i a g r a m o f t h e ICP i t s e l f i s g i v e n i n F i g u r e 2. The two e s s e n t i a l p a r t s , t o r c h and l o a d c o i l , a r e i n c l u d e d i n th e p i c t u r e . The t o r c h i s made f r o m t h r e e c o n c e n t r i c q u a r t z t u b e s : t h e o u t e r , t h e i n t e r m e d i a t e and t h e n e b u l i z e r t u b e . A c c o r d i n g l y t h r e e gas f l o w s a r e employed: p l a s m a , a u x i l i a r y and n e b u l i z e r gas f l o w . The p l a s m a gas f l o w i s t h e main gas f l o w , a n d a t o r o i d a l s h a p e d p l a s m a i s f o r m e d a t t h e l o a d c o i l by i n d u c t i o n o f e n e r g y f r o m t h e r a d i o f r e q u e n c y c u r r e n t . The a u x i l i a r y g a s f l o w s e r v e s t o l i f t t h e p l a s m a o f f t h e i n t e r m e d i a t e t u b e t o p r e v e n t m e l t i n g o f t h e t o r c h and i s not a l w a y s r e q u i r e d . The sample a e r o s o l i s i n t r o d u c e d a x i a l l y t h r o u g h t h e n e b u l i z e r t u b e i n t o t h e c e n t r a l ( o r a e r o s o l ) c h a n n e l . E n e r g y f r o m t h e t o r o i d a l r e g i o n i s t r a n s f e r r e d i n t o t h e c e n t r a l c h a n n e l by d i f f u s i o n and t h e s a m p l e i s a t o m i z e d , e x c i t e d and i o n i z e d a s i t t r a v e l s t h r o u g h t h e p l a s m a . The s t r o n g e s t a n a l y t e e m i s s i o n i n t e n s i t y i s n o r m a l l y o b s e r v e d a t 10 t o 20 mm above t h e l o a d c o i l and o r i g i n a t e s f r o m i o n i c and a t o m i c s p e c i e s . The t e r m s , e n e r g y a d d i t i o n zone, i n i t i a l r a d i a t i o n zone and n o r m a l a n a l y t i c a l zone were c o i n e d by K o i r t y o h a n n e t a l . [3] and a r e g e n e r a l l y a c c e p t e d . Two v e r s i o n s o f t h e ICP a r e i n u s e . The l o w power a r g o n - I C P u s e s a r e l a t i v e l y s m a l l t o r c h and low f l o w r a t e s 6 Torch Tail Plume Gas Flows { Plasma Auxiliary Nebulizer Normal Analytical Zone Initial Radiation Zone Induction Region Preheating Zone Outer \ Intermediate > tubes Nebulizer J F i g u r e 2. The I n d u c t i v e l y C o u p l e d P l a s m a . 7 o f a r g o n . R a d i o f r e q u e n c i e s b e t w e e n 27 and 50 MHz a r e u s e d and t h e r f i n p u t power i s between 0.5 and 2.5 kW. H i g h power n i t r o g e n / a r g o n - I C P s u s e l a r g e r t o r c h e s and f l o w r a t e s and t h e p l a s m a g a s f l o w c o n s i s t s o f n i t r o g e n . F r e q u e n c i e s a r e b e t w e e n 4 and 27 MHz and power i n p u t b e t w e e n 4 and 7 kW. The two t y p e s o f ICPs show q u i t e d i f f e r e n t c h a r a c t e r i s t i c s . The work r e p o r t e d h e r e i n was done w i t h a l o w p o w e r A r - I C P and the r e f e r e n c e s t o p u b l i c a t i o n s made a r e c o n c e r n e d w i t h t h i s t y p e of t h e ICP e x c e p t where s p e c i f i c a l l y s t a t e d o t h e r w i s e . I n d u c t i v e l y c o u p l e d p l a s m a s p e c t r o s c o p y and i t s a p p l i c a t i o n s have been r e v i e w e d r e p e a t e d l y [ 4 - 1 0 ] . 1.3 APPLICATIONS TO ORGANIC SAMPLES AND NONMETALS The f i r s t r e p o r t on t h e u s e o f ICP-OES f o r an o r g a n i c m a t r i x a p p e a r e d i n 1968 [ 1 1 ] . D e t e c t i o n l i m i t s f o r A l , Fe and N i i n o i l w e r e g i v e n . G r e e n f i e l d and S m i t h p r e s e n t e d w o r k i n g c u r v e s f o r a few m e t a l s i n e n g i n e o i l d i l u t e d w i t h x y l e n e i n 1972 [12] and i n 1976 F a s s e l e t a l . [13] p r e s e n t e d a more t h o r o u g h i n v e s t i g a t i o n i n t o the d e t e r m i n a t i o n o f wear m e t a l s i n l u b r i c a t i n g o i l s w i t h an ICP. The d e t e r m i n a t i o n of t r a c e m e t a l s i n a v a r i e t y o f p e t r o l e u m p r o d u c t s h a s s u b s e q u e n t l y been r e p o r t e d [14,15], The use of an ICP-OES as an e l e m e n t s e l e c t i v e d e t e c t o r i n l i q u i d c h r o m a t o g r a p h y when u s i n g an o r g a n i c m o b i l e phase was f i r s t r e p o r t e d by Gas t e t 8 a l . i n 1979 [ 1 6 ] and l a t e r by H a u s l e r and T a y l o r i n 1981 [17,18]. In t h e s e s t u d i e s o r g a n o m e t a l l i c compounds were used and e m i s s i o n , f r o m m e t a l s o n l y ( e x c e p t i o n s i l i c o n ) was d e t e c t e d . S e v e r a l o f t h e e a s i l y a c c e s s i b l e n o n m e t a l s h a v e b e e n d e t e r m i n e d i n aqueous s o l u t i o n s , and W i n d s o r and Denton have d e m o n s t r a t e d e l e m e n t a l a n a l y s i s o f v o l a t i l e o r g a n i c c o m p o u n d s i n t r o d u c e d a s v a p o u r s by ICP-OES [ 1 9 ] . T h e y u s e d w a v e l e n g t h s between 190 and 660 nm and measured th e e l e m e n t s B, C, H, I , P, S and S i . The i m p o r t a n t e l e m e n t s o x y g e n and n i t r o g e n c o u l d n o t be d e t e r m i n e d , b e c a u s e no s t r o n g l i n e s a r e a v a i l a b l e i n t h i s w a v e l e n g t h r e g i o n . H e i n e , B a b i s and Denton p r o c e e d e d t o examine th e s p e c t r a l r e g i o n between 120 and 185 nm [ 2 0 ] . A vacuum s p e c t r o m e t e r was u s e d a n d t h e o p t i c a l p a t h f r o m t h e p l a s m a t o t h e s p e c t r o m e t e r p u r g e d w i t h h e l i u m t o a v o i d a b s o r p t i o n by m o l e c u l a r o x y g e n . S t r o n g e m i s s i o n l i n e s f o r 0, N and a l s o C, B r , S and CI w e r e f o u n d [ 2 0 ] , F r y and c o w o r k e r s i n a s e r i e s o f n i n e p a p e r s [ 2 1 - 2 9 ] s u r v e y e d t h e f a r r e d t o n e a r - i n f r a r e d r e g i o n (700 - 950 nm) and s e n s i t i v e l i n e s f o r N, 0, F, C I , B r , S, C and H were f o u n d . T h e y u s e d t h e s e l i n e s f o r e l e m e n t s e l e c t i v e d e t e c t i o n o f o x y g e n and n i t r o g e n i n g a s - c h r o m a t o g r a p h i c e f f l u e n t s [24,25]. E l e m e n t s e l e c t i v e d e t e c t i o n or even e l e m e n t a l a n a l y s i s o f G C - e f f l u e n t s u s i n g a t o m i c e m i s s i o n s p e c t r o s c o p y h a s 9 r e c e i v e d much a t t e n t i o n , b e c a u s e s u c h d a t a i n c r e a s e s t h e s p e c i f i c i t y o f t h e m e t h o d . H o w e v e r , m i c r o w a v e i n d u c e d -p l a s m a s h a v e p r o v e n t o be more u s e f u l t h e n I C P s b e c a u s e t h e i r l o w e r i n e r t gas c o n s u m p t i o n matches th e gas f l o w r a t e o f t h e GC b e t t e r and h e l i u m MIPs p o s s e s s h i g h e r t e m p e r a t u r e s t h e n t h e A r - I C P . E l e m e n t s e l e c t i v e d e t e c t i o n f o r c h r o m a t o g r a p h y by p l a s m a e m i s s i o n s p e c t r o s c o p y h a s b e e n r e v i e w e d by J.W. Carnahan e t a l . [ 3 0 ] . Few r e f e r e n c e s t o t h e d e t e r m i n a t i o n o f n o n m e t a l s i n o r g a n i c s o l v e n t s h a v e a p p e a r e d i n t h e l i t e r a t u r e . Of t h e t h r e e e l e m e n t s o x y g e n , n i t r o g e n and s u l p h u r , o n l y t h e two l a t t e r o n e s h a v e b e e n d e t e r m i n e d i n o r g a n i c s o l v e n t s . W a l l a c e [31,32] d e t e r m i n e d s u l p h u r i n NBS ( N a t i o n a l Bureau of S t a n d a r d s ) o i l s a m p l e s w h i c h were d i l u t e d w i t h x y l e n e or m e t h y l i s o b u t y l k e t o n e ( M I B K ) . T h r e e l i n e s a r o u n d 180 nm were t e s t e d on a p u r g e d i n s t r u m e n t . W a l l a c e [32] r e p o r t e d a d e t e c t i o n l i m i t of 0.05 mg/1 f o r s u l p h u r . H a u s l e r d e t e r m i n e d n i t r o g e n i n x y l e n e u s i n g t h e 174.3 nm l i n e on a p u r g e d i n s t r u m e n t . The d e t e c t i o n l i m i t was r e p o r t e d t o r a n g e f r o m 5 t o 100 ppm [ 3 3 ] , B o t h e l e m e n t s , s u l p h u r and n i t r o g e n h a v e a l s o been d e t e r m i n e d s u c c e s s f u l l y i n aqueous s o l u t i o n s u s i n g v a c u u m - u l t r a v i o l e t l i n e s [ 3 4,35]. 10 1.4 FUNDAMENTALS OF ORGANIC SAMPLE INTRODUCTION I f ICP-OES i s t o be s u c c e s s f u l f o r t h e d e t e r m i n a t i o n of n o n m e t a l s i n o r g a n i c s , t h e measured e m i s s i o n i n t e n s i t y has to be a s i m p l e f u n c t i o n o f t h e c o n c e n t r a t i o n o f t h e a n a l y t e i n t h e s a m p l e . H o w e v e r , i n t e r f e r e n c e e f f e c t s e x e r t e d on an o r g a n i c s a m ple as i t p a s s e s t h r o u g h a n e b u l i z e r - I C P s y s t e m a r e p o t e n t i a l l y more s e v e r e t h e n i n t h e u s u a l c a s e o f a q u e o u s s o l u t i o n s . T h e c r i t i c a l a s p e c t s o f a e r o s o l p r o d u c t i o n , t h e t o r c h , t h e p l a s m a , and t h e s p e c t r u m , a r e l i s t e d i n T a b l e I and w i l l be d i s c u s s e d b e l o w i n t h e l i g h t o f t h e c u r r e n t l i t e r a t u r e . TABLE I O r g a n i c Sample I n t r o d u c t i o n S t e p i n A n a l y s i s C r i t i c a l A s p e c t A e r o s o l P r o d u c t i o n Sample D e l i v e r y Rate N e b u l i z e r E f f i c i e n c y T o r c h Soot D e p o s i t i o n Plasma V a p o u r - E f f e c t Plasma T e m p e r a t u r e I n c o m p l e t e A t o m i z a t i o n E n t r a i n m e n t of A i r S p e c t r u m S p e c t r a l O v e r l a p w i t h M o l e c u l a r Band E m i s s i o n 11 1.4.1 AEROSOL PRODUCTION T h e t w o n e b u l i z e r t y p e s f r e q u e n t l y u s e d a r e t h e c o n c e n t r i c ( o r M e i n h a r d ) and t h e c r o s s - f l o w n e b u l i z e r . B o t h work on t h e same p r i n c i p l e . A f l o w o f l i q u i d i s s h a t t e r e d by a h i g h v e l o c i t y s t r e a m o f g a s t o p r o d u c e d r o p l e t s w i t h a more o f l e s s w e l l d e f i n e d s i z e d i s t r i b u t i o n . N e b u l i z e r c h a m b e r s a r e d e s i g n e d t o r e m o v e d r o p l e t s l a r g e r t h a n a c e r t a i n c u t o f f - d i a m e t e r t o a v o i d l o a d i n g e f f e c t s i n t h e p l a s m a and i n c o m p l e t e d e s o l v a t i o n . A l a r g e p a r t o f t h e s a m p l e e n t e r i n g t h e n e b u l i z e r i s t h e r e f o r e l o s t f o r t h e a n a l y s i s and l e a v e s t h e s p r a y chamber t h r o u g h t h e d r a i n . The f r a c t i o n o f t h e o r i g i n a l l y n e b u l i z e d s a m p l e w h i c h r e a c h e s t h e p l a s m a , d e f i n e s t h e n e b u l i z e r e f f i c i e n c y . SAMPLE DELIVERY RATE: Sample t r a n s p o r t t o t h e n e b u l i z e r i s u s u a l l y a s s u r e d by t h e VENTURI e f f e c t and g o v e r n e d by t h e POISEUILLE e q u a t i o n . T h e d e l i v e r y o r a s p i r a t i o n r a t e Q i s d e f i n e d by t h e v i s c o s i t y o f t h e s o l v e n t ^ , t h e l e n g t h of t h e c a p i l l a r y L of r a d i u s R and t h e d r i v i n g p r e s s u r e P: 8 V L Of t h e s e v a r i a b l e s t h e v i s c o s i t y and p o s s i b l y t h e 12 p r e s s u r e d i f f e r e n c e a r e s a m p l e d e p e n d e n t and t h e r e f o r e d e l i v e r y r a t e s and e m i s s i o n i n t e n s i t i e s v a r y . A l s o , t h e p r e s s u r e d i f f e r e n c e depends on t h e n e b u l i z e r gas f l o w r a t e . To make f r e e a s p i r a t i o n p o s s i b l e and a s s u r e c o n s t a n t d e l i v e r y r a t e s , v i s c o u s o i l s a m p l e s a r e d i l u t e d w i t h an a p p r o p r i a t e s o l v e n t ( s e e e.g. [ 1 3 ] ) . The l i m i t a t i o n s s e t by the POISEUILLE e q u a t i o n can a l s o be overcome by u s i n g a pump t o c o n t r o l t h e f l o w o f sample t o t h e n e b u l i z e r ( f o r c e - f e d as o p p o s e d t o f r e e a s p i r a t i o n ) ( s e e e.g. [ 3 6 , 3 2 ] ) . NEBULIZER EFFICIENCY: The d r o p l e t s i z e d i s t r i b u t i o n i s an i m p o r t a n t p a r a m e t e r to be c o n s i d e r e d , s i n c e t h e f i n e r t h e a e r o s o l i s , t h e h i g h e r the n e b u l i z e r e f f i c i e n c y and t h e e m i s s i o n i n t e n s i t y w i l l be. No e x a c t t h e o r e t i c a l model i s a v a i l a b l e t o p r e d i c t d r o p l e t s i z e d i s t r i b u t i o n , but an e m p i r i c a l f o r m u l a , t h e NUKIYAMA-TANASAWA e q u a t i o n , o r i g i n a l l y d e s i g n e d t o d e s c r i b e c a r b u r e t o r o p e r a t i o n i s u s u a l l y q u o t e d . I t s v a l i d i t y f o r c o n c e n t r i c n e b u l i z e r s u s e d i n a t o m i c s p e c t r o s c o p y h a s r e c e n t l y been t h o r o u g h l y examined by G u s t a v s s o n [37,38]. d0 = 585 + 597 term do = mean d r o p l e t d i a m e t e r ( m) , x> = v e l o c i t y o f gas (m/s) 0* = s u r f a c e t e n s i o n (dyne/cm), = v i s c o s i t y ( p o i s e ) f = d e n s i t y o f t h e l i q u i d (g/ml) Q-^  = volume f l o w l i q u i d , Q = volume f l o w gas 13 c r / / ' a n d y u a r e l i q u i d p r o p e r t i e s and t h e r e f o r e t h e s i z e d i s t r i b u t i o n v a r i e s as d i f f e r e n t s a m p l e s a r e u s e d f o r a g i v e n n e b u l i z e r . M o r e o v e r , e v a p o r a t i o n o f s o l v e n t f r o m t h e d r o p l e t s s e r v e s t o change t h e o r i g i n a l s i z e d i s t r i b u t i o n . C r e s s e r and B r o w n e r h a v e p r e s e n t e d an e q u a t i o n t o p r e d i c t e v a p o r a t i o n f r o m d r o p l e t s [ 3 9 ] , a n d B o o r n e t a l . h a v e p u b l i s h e d t h e o r e t i c a l d a t a on a s e r i e s o f s o l v e n t s b a s e d on t h a t e q u a t i o n [ 4 0 ] , O b v i o u s l y s p r a y chamber t e m p e r a t u r e w i l l have an e f f e c t on e v a p o r a t i o n , and h e a t i n g d u r i n g an a n a l y s i s and t h e r e s u l t a n t d r i f t o f n e b u l i z e r e f f i c i e n c y c a n c a u s e i n s t a b i l i t i e s i n t h e o b s e r v e d a n a l y t i c a l s i g n a l [ 1 7 ] , To o v e r c o m e t h i s p r o b l e m , H a u s l e r and T a y l o r h a v e u s e d a j a c k e t e d w a t e r c o o l e d s p r a y c h a m b e r [ 1 7 ] . A d i f f e r e n t a p p r o a c h i s t o l o c a t e t h e s p r a y c h a m b e r d i s t a n t f r o m t h e p l a s m a o u t s i d e t h e p l a s m a box [ 3 6 ] . B o t h , d e l i v e r y r a t e and n e b u l i z e r e f f i c i e n c y , c a u s e l a r g e r a m o u n t s o f o r g a n i c s o l v e n t s t o r e a c h t h e p l a s m a ( h i g h e r t r a n s p o r t e f f i c i e n c y ) c o m p a r e d t o w a t e r and t h e e m i s s i o n i n t e n s i t y i n ICP-OES i s h i g h e r . T h e r e f o r e t h e t e r m ' s o l v e n t e n h a n c e m e n t e f f e c t s ' h a s b e e n u s e d . N e b u l i z e r e f f i c i e n c i e s f o r a c o n t r o l l e d a s p i r a t i o n r a t e were r e p o r t e d t o be 22, 8, 6, and 1.5 % f o r b e n z e n e , x y l e n e , n i t r o b e n z e n e and w a t e r r e s p e c t i v e l y [ 4 1 ] . R e v i e w s o f a e r o s o l p r o d u c t i o n i n a t o m i c s p e c t r o s c o p y h a v e b e e n c o m p i l e d by C r e s s e r [ 3 8 ] 14 and Browner and Boorn [39,40]. 1.4.2 TORCH The d e s i g n o f t h e t o r c h has p r o v e n t o be c r i t i c a l when o r g a n i c a e r o s o l s a r e i n t r o d u c e d i n t o t h e ICP. F a s s e l e t a l . r e p o r t e d c a r b o n l i k e d e p o s i t s on t h e r i m s o f t h e two i n n e r t u b e s o f t h e t o r c h when MIBK o r x y l e n e was a s p i r a t e d [ 1 3 ] , and Boumans and L u x - S t e i n e r h a v e d e s c r i b e d an o p t i m i z e d t o r c h d e s i g n f o r o r g a n i c a e r o s o l s t o overcome t h i s p r o b l e m [ 4 5 ] , The f o l l o w i n g s u m m a r i z e s t h e m a i n f e a t u r e s f o u n d d e s i r a b l e : (1) A T u l i p s h a p e d i n t e r m e d i a t e t u b e , o u t e r d i a m e t e r o f t h a t t u b e as l a r g e as ease o f i g n i t i o n would a l l o w . (2) T a p e r e d r i m s o f i n n e r and i n t e r m e d i a t e tube. (3) The r i m o f t h e n e b u l i z e r t u b e l o c a t e d s l i g h t l y below t h e r i m o f t h e i n t e r m e d i a t e t u b e . In a d d i t i o n , G r e e n f i e l d e t a l . [46] s u g g e s t e d , t h a t t h e top o f t h e n e b u l i z e r t u b e p o s s e s s e s a l o n g , narrow c h a n n e l . T h i s p r o v i d e d f o r e f f i c i e n t p e n e t r a t i o n o f t h e a e r o s o l i n t o t h e p l a s m a and t h e r e f o r e good s t a b i l i t y . 15 1.4.3 PLASMA VAPOUR EFFECT AND PLASMA TEMPERATURE: B o o r n a n d B r o w n e r h a v e p u b l i s h e d a n e x t e n s i v e i n v e s t i g a t i o n on t h e e f f e c t s o f o r g a n i c s o l v e n t s on t h e ICP i t s e l f [ 3 6 ] . T h e y f o u n d , t h a t t h e maximum a s p i r a t i o n r a t e c o m p a t i b l e w i t h s t a b l e o p e r a t i o n was s t r o n g l y c o r r e l a t e d w i t h a t h e o r e t i c a l s o l v e n t e v a p o r a t i o n f a c t o r . T h e e v a p o r a t i o n f a c t o r i s a m e a s u r e o f t h e r a t e w i t h w h i c h t h e s o l v e n t e v a p o r a t e s f r o m a e r o s o l d r o p l e t s . The maximum a s p i r a t i o n r a t e was d e f i n e d a s t h e h i g h e s t p o s s i b l e r a t e w h i c h d i d not c a u s e a p p r e c i a b l e c a r b o n d e p o s i t s on t h e t o r c h a f t e r one hour o f o p e r a t i o n . They measured l i n e i n t e n s i t i e s f o r m e t a l s i n d i f f e r e n t s o l v e n t s and f o u n d i n t e n s i t i e s i n v o l a t i l e s o l v e n t s l o w e r t h a n e x p e c t e d by t r a n s p o r t e f f i c i e n c y c o n s i d e r a t i o n s . They a r g u e d , t h a t s o l v e n t vapour l o a d i n g c a u s e s l o w e r i n g o f t h e t e m p e r a t u r e i n t h e p l a s m a . F r o m some s p a t i a l l y r e s o l v e d e m i s s i o n d a t a t h e y a l s o c o n c l u d e d , t h a t t h e v a p o u r l o a d i n g e f f e c t was m o r e s i g n i f i c a n t low i n t h e p l a s m a . In c o n t r a s t , h i g h power Ar/N-ICPs pose no d i f f i c u l t i e s w i t h r e s p e c t t o t h e vapour e f f e c t , a n d h i g h l y v o l a t i l e s o l v e n t s ( e . g . a c e t o n e ) c a n be i n t r o d u c e d w i t h o u t any p r o b l e m s [ 4 7 ] . Boumans and L u x - S t e i n e r [45] u n d e r t o o k a d e t a i l e d s t u d y o f a 50 MHz l o w p o w e r ICP w i t h m e t a l s i n MIBK t o f i n d 16 o p t i m u m a n a l y t i c a l c o n d i t i o n s ( d e t e c t i o n l i m i t s ) w i t h r e s p e c t t o f l o w r a t e s , r f i n p u t power, sample f e e d r a t e and v i e w i n g h e i g h t . T h e y f o u n d t h a t an i n p u t p o w e r b e t w e e n 1.4 and 1.8 kW f o r MIBK a s p i r a t i o n p r o d u c e d s i m i l a r e x c i t a t i o n c o n d i t i o n s t o t h o s e w i t h w a t e r a s p i r a t i o n b e t w e e n 0.8 and 1.4 kW. A s i m i l a r s t u d y by M i y a z a k i e t a l . [ 4 8 ] u s i n g d i i s o o c t y l k e t o n e (DIBK) s u g g e s t e d a g a i n t h a t t h e m a j o r d i f f e r e n c e t o an aqueous p l a s m a ( t h e t e r m s 'aqueous p l a s m a , x y l e n e p l a s m a , o r g a n i c p l a s m a ' e t c . w i l l be used t o r e f e r to the t y p e o f a e r o s o l i n t r o d u c e d ) was t h e need f o r an i n c r e a s e i n r f i n p u t power by ab o u t 0.5 kW when o p t i m i z i n g s i g n a l to n o i s e r a t i o s (S/N) f o r m e t a l s . To f u r t h e r c l a r i f y t h i s power a s p e c t , B l a d e s and C a u g h l i n [ 4 9 ] h a v e a c q u i r e d s p a t i a l l y r e s o l v e d i n f o r m a t i o n on t e m p e r a t u r e s i n a x y l e n e p l a s m a ; x y l e n e b e i n g a common s o l v e n t used f o r t h e d e t e r m i n a t i o n o f m e t a l s i n o i l s . They f o u n d , t h a t t e m p e r a t u r e s g e n e r a l l y a r e l o w e r i n t h e x y l e n e p l a s m a c o m p a r e d t o t h e a q u e o u s one and an i n c r e a s e o f about 0.5 kW y i e l d s t h e same t e m p e r a t u r e s f o r t h e x y l e n e p l a s m a . T h e s e t h r e e l a t t e r s t u d i e s s h o w e d t h a t t h e I CP i s q u e n c h e d e v e n by s o l v e n t s w i t h h i g h e r b o i l i n g p o i n t s t h a n w a t e r . The e v a p o r a t i o n f a c t o r s o f x y l e n e and w a t e r i n p a r t i c u l a r a r e v e r y c l o s e [ 3 6 ] , s o t h a t t h e q u e n c h i n g o f t h e p l a s m a c a n n o t be a t t r i b u t e d t o t h e v a p o u r e f f e c t a l o n e . T h e r e f o r e a f u r t h e r o r g a n i c q u e n c h i n g e f f e c t must t a k e p l a c e . Boumans and L u x - S t e i n e r s u g g e s t e d , t h a t t h e 17 p r e s e n c e o f o r g a n i c s o l v e n t l e a d s t o i n c r e a s e d e n t h a l p h y of the c a r r i e r gas and t h e p r e s e n c e o f m o l e c u l a r c o n s t i t u e n t s i n c r e a s e s t h e t h e r m a l c o n d u c t i v i t y o f t h e p l a s m a and so r e q u i r e s h i g h e r i n p u t p o w e r t o a c h i e v e s i m i l a r e x c i t a t i o n c o n d i t i o n s [ 4 5 ] . A l s o i t h a s t o be c o n s i d e r e d , t h a t t r a n s p o r t e f f i c i e n c i e s a r e h i g h e r f o r o r g a n i c s o l v e n t s and t h e r e f o r e a l s o t h e s a m p l e l o a d . W h a t e v e r t h e c a u s e s , t h e e x c i t a t i o n t e m p e r a t u r e i n an o r g a n i c p l a s m a can be e x p e c t e d t o be g e n e r a l l y l o w e r f o r a g i v e n p o w e r when a n a l y s i n g o r g a n i c s a m p l e s and t h e v a p o u r e f f e c t l i m i t s t h e u s e o f h i g h l y v o l a t i l e l i q u i d s . INCOMPLETE ATOMIZATION: B o o r n and B r o w n e r [ 3 6 ] h a v e a l s o l i s t e d a number o f m o l e c u l a r s p e c i e s d e t e c t e d when o r g a n i c s were a s p i r a t e d . The o b s e r v e d d i a t o m i c f r a g m e n t s ( C 2 , CH, CN, CS, OH, NH, NO and CC1) w e r e d e t e c t e d by t h e i r e m i s s i o n b a n d s . T h e y a l s o p r e s e n t e d p l o t s o f e m i s s i o n i n t e n s i t y as a f u n c t i o n o f h e i g h t a l o n g t h e c e n t r a l a x i s f o r C I , C 2 and CN f o r s e v e r a l s o l v e n t s . CI and C 2 i n t e n s i t i e s s t e a d i l y d e c r e a s e d f r o m th e l o w e s t h e i g h t measured (5mm) whereas CN i n c r e a s e d f i r s t t o p eak a t a b o u t 15 mm a b o v e t h e l o a d c o i l . F o r p y r i d i n e , t h e o n l y n i t r o g e n c o n t a i n i n g s o l v e n t , an i n t e n s e CN p e a k was f o u n d low i n t h e p l a s m a . S i m i l a r s t u d i e s had been c o n d u c t e d by T r u i t t and R o b i n s o n w i t h s o l v e n t s i n t r o d u c e d as v a p o u r s 18 [ 5 0 ] . E m i s s i o n f r o m a m o l e c u l a r band o f NH h a s b e e n u s e d f o r the d e t e r m i n a t i o n o f n i t r o g e n [ 5 1 ] . The p r e s e n c e o f t h e s e m o l e c u l a r s p e c i e s i n d i c a t e s t h a t a t o m i z a t i o n i s not c o m p l e t e ( a l t h o u g h f r a g m e n t a t i o n t o the d i a t o m i c l e v e l i s o b v i o u s l y a c h i e v e d ) , a t l e a s t n o t a t a l l l o c a t i o n s i n t h e p l a s m a . T h i s c o u l d g i v e r i s e t o p o o r s e n s i t i v i t y , when m e a s u r i n g e m i s s i o n f r o m t h e n o n m e t a l s w h i c h a r e p a r t o f a c o m p l e x o r g a n i c m o l e c u l e . A l s o , t h e d e g r e e o f a t o m i z a t i o n m i g h t v a r y f o r d i f f e r e n t m o l e c u l a r s t r u c t u r e s b e c a u s e o f d i f f e r e n c e s i n bond s t r e n g t h and c a u s e a m a t r i x i n t e r f e r e n c e e f f e c t . Northway and F r y [21] have i n v e s t i g a t e d t h i s p o t e n t i a l i n t e r f e r e n c e e f f e c t f o r g a s e o u s s a m p l e i n t r o d u c t i o n . The oxygen e m i s s i o n i n t e n s i t i e s f r o m e q u a l v o l u m e s of 0 2 and CO ga s w e r e c o m p a r e d and t h e i r r a t i o p l o t t e d a s a f u n c t i o n o f r f i n p u t power. They f o u n d t h a t t h e t h e o r e t i c a l r a t i o o f 2:1 was o n l y a c h i e v e d a t an i n p u t p o w e r a s h i g h a s 2 k W. T h e r e f o r e a s t r u c t u r a l i n t e r f e r e n c e e f f e c t i s i n d i c a t e d f o r o x y g e n d e t e r m i n a t i o n s when t h e r f i n p u t p o w e r i s n o t s u f f i c i e n t and p o s s i b l y a l s o when o t h e r o p e r a t i n g c o n d i t i o n s ( g a s f l o w r a t e s , v i e w i n g h e i g h t ) a r e n o t f a v o u r a b l e . Northway and F r y ch o s e CO f o r t h e i r i n v e s t i g a t i o n b e c a u s e i t i s t h e m o l e c u l e w i t h t h e h i g h e s t d i s s o c i a t i o n e n e r g y (11.1 e V ) . 19 ENTRAINMENT OF AIR: When d e t e r m i n i n g o x y g e n and n i t r o g e n , c o n t a m i n a t i o n p o s e s a m a j o r i n t e r f e r e n c e p r o b l e m , b e c a u s e t h e p l a s m a i s e x p o s e d t o s u r r o u n d i n g a i r . F r y a n d c o - w o r k e r s h a v e p r e s e n t e d p l o t s o f o x y g e n [ 2 4 ] and n i t r o g e n [ 2 2 ] e m i s s i o n i n t e n s i t i e s a s a f u n c t i o n o f v i e w i n g h e i g h t t o i l l u s t r a t e t h i s e n t r a i n m e n t and s u g g e s t e d t h e use of an e x t e n d e d t o r c h to e x c l u d e a t m o s p h e r i c g a s e s [ 2 4 ] . They a l s o r e p o r t e d oxygen and n i t r o g e n c o n t a m i n a t i o n o f t h e a r g o n g a s w h i c h was a t t r i b u t e d t o i m p u r i t i e s i n t h e t a n k and l e a k a g e i n t o t h e t u b i n g . F r y e t a l . have a l s o shown t h a t e m i s s i o n i n t e n s i t i e s o f o x y g e n , s u l p h u r and c a r b o n d e c a y e d l e s s r a p i d l y w i t h v i e w i n g h e i g h t when e x t e n d e d t o r c h e s w e r e u s e d . T h i s was e x p l a i n e d by t h e l a c k o f q u e n c h i n g o f t h e p l a s m a by a t m o s p h e r i c N2> CO2 and 0 2 [24,28,52], 1.4.4 SPECTRUM Band e m i s s i o n f r o m m o l e c u l e s c a n c a u s e c o n s i d e r a b l e s p e c t r a l i n t e r f e r e n c e . E v e n a q u e o u s p l a s m a s e x h i b i t some m o l e c u l a r e m i s s i o n due t o m o l e c u l e s f o r m e d w i t h e n t r a i n e d a t m o s p h e r i c g a s e s . W a l l a c e [53] s u g g e s t e d t h e use of a t o r c h e x t e n s i o n t o r e d u c e some i n t e r f e r e n c e s c a u s e d by NO, OH and CN e m i s s i o n . N a t u r a l l y , m o l e c u l a r e m i s s i o n i s more s e v e r e when o r g a n i c s a r e i n t r o d u c e d and s p e c t r a l o v e r l a p s more 20 n u m e r o u s . B o o r n and B r o w n e r [ 3 6 ] h a v e l i s t e d a number o f s u c h p o t e n t i a l i n t e r f e r e n c e s and t h i s a s p e c t has a l s o been i n v e s t i g a t e d by Xu e t a l . [ 5 4 ] . 1.4 . 5 SUMMARY T h e l i t e r a t u r e r e v i e w h a s l e d t o t h e f o l l o w i n g c o n c l u s i o n s . S a m p l e s w i t h d i f f e r e n t p h y s i c a l p r o p e r t i e s c o u l d n o t be c o m p a r e d , b e c a u s e o f t h e e f f e c t s t a k i n g p l a c e a t t h e a e r o s o l p r o d u c t i o n s t e p , and t h e r e f o r e m a t r i c e s s h o u l d be m a t c h e d by d i l u t i o n . The s p r a y c h a m b e r s h o u l d be c o o l e d t o m i n i m i z e i n s t a b i l i t i e s c a u s e d by h e a t b u i l d up i n t h e p l a s m a box. A s p e c i a l t o r c h f o r o r g a n i c a e r o s o l s must be used. The r f i n p u t power s h o u l d be s e t h i g h t o m a x i m i z e the d e g r e e o f a t o m i z a t i o n , and t h i s p o t e n t i a l i n t e r f e r e n c e s h o u l d be e x a m i n e d . An e f f e c t i v e s o l u t i o n t o t h e i n t e r f e r e n c e f r o m e n t r a i n e d a i r must be f o u n d . A s u r v e y o f t h e r e p o r t e d n o n m e t a l NIR l i n e s s h o u l d be c a r r i e d o u t t o f i n d t h e m o s t i n t e n s e l i n e s f o r t h e x y l e n e p l a s m a and t h e c h o s e n l i n e s had t o be e x amined f o r s p e c t r a l o v e r l a p s w i t h m o l e c u l a r band e m i s s i o n . The s t u d y r e p o r t e d i n t h e f o l l o w i n g c h a p t e r s was done i n e s s e n t i a l l y t h r e e s t e p s . F i r s t , a n a l y t i c a l l i n e s w e r e e s t a b l i s h e d and t h e c o m p l e t e n e s s o f a t o m i z a t i o n e x a m i n e d . S e c o n d l y , t h e i n t e r f e r e n c e f r o m a i r was i n v e s t i g a t e d and 21 o p e r a t i n g c o n d i t i o n s o p t i m i z e d . F i n a l l y , t h e f e a s i b i l i t y of th e method was t e s t e d by c o m p a r i n g t h e r e s p o n s e f r o m s a m p l e s of d i f f e r e n t c o m p o s i t i o n , e s t a b l i s h i n g d e t e c t i o n l i m i t s and w o r k i n g c u r v e s and by a n a l y s i n g c e r t i f i e d s a m p l e s . 22 CHAPTER I I EXPERIMENTAL 2.1 INSTRUMENTATION A b l o c k d i a g r a m o f t h e i n s t r u m e n t a t i o n i s g i v e n i n F i g u r e 3. The ICP u s e d was a c o m m e r c i a l l y a v a i l a b l e u n i t m a n u f a c t u r e d by P l a s m a - T h e r m Inc., K r e s s o n N.J. The s o u r c e c o n s i s t e d o f a HFP-2500E, 27.18 MHz, 2.5 kW r a d i o f r e q u e n c y g e n e r a t o r , an AMN-2500E a u t o m a t i c m a t c h i n g network, an APCS1 a u t o m a t i c p o w e r c o n t r o l s y s t e m and a P T - 2 5 0 0 p l a s m a t o r c h a s s e m b l y . A c o n c e n t r i c g l a s s n e b u l i z e r ( P l a s m a - T h e r m Inc., model GN 5601) was used f o r sample i n t r o d u c t i o n . F r e e sample u p t a k e was employed e x c e p t were m e n t i o n e d . The s p r a y chamber was o f t h e c o n v e n t i o n a l c o n c e n t r i c b a r r e l t y p e ( P l a s m a - T h e r m Inc., model SC-5037). To m i n i m i z e i n s t a b i l i t i e s due t o h e a t b u i l d up i n t h e p l a s m a box t h e s p r a y c h a m b e r was w a t e r c o o l e d u s i n g a c o i l o f t i g h t l y w r a p p e d p l a s t i c t u b i n g . The w a t e r t e m p e r a t u r e was a p p r o x i m a t e l y 10 °C. A 0.35 m C z e r n y - T u r n e r m o n o c h r o m a t o r ( M o d e l 270, S c h o e f f e 1 - M c P h e r s o n , A c t o n MA) w i t h a g r a t i n g w i t h 1200 grooves/mm b l a z e d a t 500 nm was used. An image of t h e p l a s m a was f o r m e d a t t h e e n t r a n c e s l i t o f t h e m o n o c h r o m a t o r by a p l a n o - c o n v e x f u s e d s i l i c a l e n s o f 50 mm d i a m e t e r and 150 mm f o c a l l e n g t h . The i m a g i n g d i s t a n c e was a d j u s t e d t o p r o v i d e Sample Nebulizer and Spray Chamber Translation Stage I I C P T Lens i Monochromator Ar- Supply Rf- Generator Oscilloscope < I Monitor Printer Digital Plotter Floppy-Disc Drive F i g u r e 3. B l o c k D i a g r a m o f t h e I n s t r u m e n t a t i o n . 24 an image m a g n i f i c a t i o n of 1. The v i e w i n g h e i g h t was a l t e r e d by moving the l e n s v e r t i c a l l y . The e n t r a n c e s l i t was lOO^tm w i d e and i t s h e i g h t r e s t r i c t e d t o 1 mm by an a p e r t u r e . A l o n g p a s s f i l t e r ( O p t i c o n , m o d e l RG63) was u s e d t o c u t o f f w a v e l e n g t h s s h o r t e r t h a n 630 nm t o p r e v e n t m u l t i p l e o r d e r i n t e r f e r e n c e s . A l l t h r e e e l e m e n t s , I C P , l e n s a n d m o n o c h r o m a t o r w e r e m o u n t e d and a l i g n e d on an o p t i c a l r a i l b e d . The d e t e c t o r u s e d was a 1024 e l e m e n t p h o t o d i o d e a r r a y ( R e t i c o n RL-1024S) mounted i n t h e e x i t f o c a l p l a n e o f t h e monochromator. The d i m e n s i o n s of t h e t o t a l l i g h t s e n s i n g a r e a w e r e 25.5 mm by 2.5 mm. T h i s p r o v i d e d f o r a s i m u l t a n e o u s r e a d o u t o f a s p e c t r a l w indow w h i c h was 38 nm w i d e a t 900 nm. E l e c t r o n i c r e a d o u t o f t h e p h o t o d i o d e a r r a y was a c c o m p l i s h e d w i t h an RC-1024SA e v a l u a t i o n b o a r d f r o m R e t i c o n . The i n t e g r a t i o n t i m e c a p a b i l i t y o f t h i s b o a r d h a s been i n c r e a s e d by a d d i n g 9316 i n t e g r a t e d c i r c u i t c o u n t e r s as d e s c r i b e d i n R e f . [ 5 5 ] , so t h a t i t c o u l d be v a r i e d b e t w e e n 50 ms and 10 s i n 50 ms i n c r e m e n t s . The a r r a y o u t p u t s i g n a l was d i s p l a y e d on an o s c i l l o s c o p e ( K i k i s u i , M o d e l 5 6 5 0 ) . A n a l o g t o d i g i t a l c o n v e r s i o n o f t h e a r r a y a n a l o g r e a d o u t was a c h i e v e d by a A I 1 3 1 2 - b i t a n a l o g t o d i g i t a l c o n v e r t e r f r o m I n t e r a c t i v e S t r u c t u r e s ( B a t a - C y n w y d , PA). The d i g i t i z e d o u t p u t was a c q u i r e d w i t h an A p p l e I I p l u s m i c r o c o m p u t e r , w h i c h was a l s o u s e d t o c o n t r o l t h e o p e r a t i o n o f , and d a t a a c q u i s i t i o n f r o m t h e a r r a y e v a l u a t i o n b o a r d ( i n c l u d i n g 25 i n t e g r a t i o n t i m e ) a n d t h e d i g i t a l t o a n a l o g c o n v e r t e r by a 6502 m a c h i n e l a n g u a g e p r o g r a m . F u r t h e r d a t a p r o c e s s i n g ( s i g n a l a v e r a g i n g , b a c k g r o u n d s u b t r a c t i o n , A b e l i n v e r s i o n e t c . ) was done i n A p p l e s o f t B a s i c . S p e c t r a and p r o c e s s e d d a t a w e r e s t o r e d on 5 1/4 i n c h f l o p p y d i s c s and d i s p l a y e d on t h e A p p l e m o n i t o r , on a d i g i t a l p l o t t e r (WATANABE WX 4671) or a p r i n t e r (OKIDATA 92). The p l a s m a box was m o u n t e d on a l i n e a r t r a n s l a t i o n s t a g e d r i v e n by a s t e p p e r m o t o r ( D a e d a l I n c . m o d e l 4979, H a r r i s o n C i t y , PA) w h i c h a l l o w e d h o r i z o n t a l movement p e r p e n d i c u l a r t o t h e o p t i c a l a x i s i n i n c r e m e n t s o f 0.0127 mm. A c o m b i n a t i o n o f m o v e m e n t s o f t h e l e n s a n d t h e t r a n s l a t i o n s t a g e t h u s e n a b l e d o b s e r v a t i o n o f any d e s i r e d r e g i o n o f t h e p l a s m a . The t r a n s l a t i o n s t a g e was i n t e r f a c e d to t h e m i c r o c o m p u t e r so t h a t i t s movements c o u l d be s o f t w a r e c o n t r o l l e d . A p i s t o n pump (model NH-SY, F l u i d M e t e r i n g Inc., O y s t e r Bay, NY) was u s e d i n e x p e r i m e n t s w h e r e c o n t r o l l e d s a m p l e d e l i v e r y was e m p l o y e d . P u l s e s w e r e d a m p e d by a f e w m i l l i l i t r e s o f a i r c o n t a i n e d i n a s y r i n g e c o n n e c t e d t o t h e s o l v e n t l i n e downstream from t h e pump. The a r g o n s u p p l y was of w e l d i n g g r a d e and r e a g e n t g r a d e c h e m i c a l s were g e n e r a l l y used. A m i x t u r e of x y l e n e i s o m e r s was used as t h e s o l v e n t . An r f i n p u t p o w e r o f 2 kW was u s e d t h r o u g h o u t t h e s t u d y 26 and and t h e t h e p l a s m a and a u x i l i a r y g a s f l o w r a t e s 2 l / m i n r e s p e c t i v e l y . The n e b u l i z e r g a s v i e w i n g h e i g h t v a r i e d . w e r e f l o w 12 l / m i n r a t e and 2.2 TORCH The q u a r t z t o r c h was c o n s t r u c t e d a t t h e UBC g l a s s shop f r o m p r e c i s i o n - b o r e q u a r t z t u b i n g . The d i m e n s i o n s a r e p r o v i d e d i n F i g u r e 4. The t o r c h s h o w s some o f t h e f e a t u r e s f o u n d d e s i r a b l e f o r o r g a n i c a e r o s o l s by Boumans and L u x -S t e i n e r [ 4 5 ] . I t was d e s i g n e d t o t o l e r a t e h i g h a s p i r a t i o n r a t e s o f o r g a n i c s o l v e n t s w i t h o u t e x t i n c t i o n o f t h e p l a s m a a n d t o be r e s i s t a n t t o s o o t b u i l d u p on a e r o s o l a n d i n t e r m e d i a t e t u b e s . U s i n g b o t h c r i t e r i a our t o r c h compares w e l l w i t h t h o s e u s e d by o t h e r a u t h o r s . Xu e t a l . [ 5 4 ] r e p o r t e d t h a t t h e i r 27 MHz Ar p l a s m a was e x t i n g u i s h e d when more t h a n 1 % a c e t o n e was mixed to w a t e r a s p i r a t e d i n t o t h e p l a s m a v i a a c o n c e n t r i c n e b u l i z e r . No d a t a on t h e t o r c h was g i v e n . I t was f o u n d t h a t o u r t o r c h t o l e r a t e d a t l e a s t 70 % a c e t o n e i n w a t e r when o p e r a t e d w i t h th e same f l o w r a t e s and r f p o w e r a s Xu e t a l . B o o r n an d B r o w n e r [ 3 6 ] r e p o r t e d o p e r a t i o n f r e e o f c a r b o n d e p o s i t s f o r a c o n t r o l l e d a s p i r a t i o n r a t e o f 0.1 m l / m i n a c e t o n e v i a a c r o s s - f l o w n e b u l i z e r f o r a p e r i o d o f one h o u r . The t o r c h t h e y u s e d was a P l a s m a T h e r m M o d e l T1.0. U s i n g t h e i r w o r k i n g c o n d i t i o n s 27 and c r i t e r i a , d e l i v e r y r a t e i t was as h i g h f o u n d as 0.4 t h a t o u r a s s e m b l y t o l e r a t e d m l / m in a c e t o n e . T F i g u r e 4. ICP T o r c h D i m e n s i o n s : A 20.37 mm, B 17.39 mm, C 15.86 mm, D 5 mm, E 1.48 mm, F 20 mm, G 20 mm, H 43 mm, I 20 mm, K 25 mm, L 1 mm, M 3 mm. 2.3 ACQUISITION OF EMISSION PROFILES A f t e r c h o o s i n g t h e d e s i r e d v i e w i n g h e i g h t , p r o f i l e s of e m i s s i o n i n t e n s i t y w e r e a c q u i r e d i n t h e f o l l o w i n g manner. The t r a n s l a t i o n s t a g e was moved i n 100 i n c r e m e n t s o f 0.1905 mm e a c h t o a l l o w t h e measurement o f e m i s s i o n i n t e n s i t i e s a t 100 l o c a t i o n s a c r o s s t h e w i d t h o f t h e p l a s m a . T h e s o o b t a i n e d l a t e r a l p r o f i l e s r e p r e s e n t e d t h e sum o f i n t e n s i t i e s t h r o u g h t h e d e p t h o f t h e p l a s m a as i l l u s t r a t e d i n F i g u r e 5. I x n s t a n d s f o r t h e o b s e r v e d l a t e r a l e m i s s i o n i n t e n s i t y a t p o s i t i o n xn. A s y m m e t r i c A b e l I n v e r s i o n [56] was t h e n u s e d t o c a l c u l a t e e m i s s i o n i n t e n s i t i e s a s a f u n c t i o n o f r a d i a l p o s i t i o n f r o m t h i s measured l a t e r a l d a t a . The r a d i i h e r e b y a r e e q u i v a l e n t t o t h e l a t e r a l d i s t a n c e s . The i n t e n s i t i e s I r n i n F i g u r e 5 r e p r e s e n t t h e c a l c u l a t e d e m i s s i o n i n t e n s i t i e s on 100 r a d i i ( r ) l e f t and r i g h t f r o m t h e c e n t r e . 29 F i g u r e 5. A s y m m e t r i c A b e l I n v e r s i o n . 30 CHAPTER I I I RESULTS AND DISCUSSION 3.1 NEAR-IR OXYGEN, NITROGEN AND SULPHUR LINES The p u b l i c a t i o n s o f F r y and h i s c o l l e a g u e s [ 2 1 , 2 2 , 2 8 ] w e r e u s e d a s a g u i d e f o r t h e s e l e c t i o n o f a n a l y t i c a l l i n e s f o r t h e d e t e r m i n a t i o n o f oxygen, n i t r o g e n and s u l p h u r . S i n c e o u r work i n v o l v e d n e b u l i z i n g x y l e n e as o p p o s e d t o g a s e o u s s a m p l i n g , a s u r v e y o f t h e s e l i n e s was c a r r i e d o u t , t o f i n d t h e most s e n s i t i v e l i n e s and t o check on p o t e n t i a l s p e c t r a l o v e r l a p s w i t h m o l e c u l a r s p e c i e s . A n e b u l i z e r gas f l o w r a t e o f 0.75 l / m i n and a v i e w i n g h e i g h t o f 10 mm f r o m t h e t o p o f t h e l o a d c o i l was employed f o r t h e s e s t u d i e s . In a g r e e m e n t w i t h F r y e t a l . i t was f o u n d t h a t t h e 777.2 nm l i n e was t h e most i n t e n s e NIR e m i s s i o n l i n e o f a t o m i c oxygen [ 2 1 ] . An e m i s s i o n s p e c t r u m o f 1 % oxygen i n x y l e n e i s p r o v i d e d i n F i g . 6. The 777.2 nm l i n e i s n o t r e s o l v e d f r o m t h e n e a r b y 777.4 and 777.5 nm 01 l i n e s , w i t h t h e r e s o l u t i o n p r o v i d e d by t h e e x p e r i m e n t a l s y s t e m d e s c r i b e d i n C h a p t e r I I . However, t h e 01 l i n e s a r e f r e e of s p e c t r a l o v e r l a p s f r o m t h e o t h e r p l a s m a c o m p o n e n t s and c o u l d t h u s be u s e d as a g r o u p f o r oxygen d e t e r m i n a t i o n s . F o r n i t r o g e n , a l l l i n e s were f o u n d to be c o m p a r a t i v e l y weak. The 868.0 nm l i n e was most i n t e n s e , a g a i n i n agreement 31 w i t h F r y e t a l . [ 2 2 ] . I n p r a c t i c e , h o w e v e r , a l i n e w i n g o v e r l a p w i t h t h e i n t e n s e 866.7 nm A r l l i n e r e s t r i c t e d t h e d y n a m i c r a n g e o f t h e NI l i n e a t l o n g a r r a y i n t e g r a t i o n t i m e s . F i g . 7 i s an e m i s s i o n s p e c t r u m i n t h e r a n g e f r o m 848 nm t o 880 nm. The 868 nm NI t r i p l e t and t h e n e a r b y A r l l i n e a r e i d e n t i f i e d i n t h e f i g u r e . As a r e s u l t o f t h i s p a r t i a l o v e r l a p t h e 821.6 NI l i n e was u s e d f o r a n a l y t i c a l d e t e r m i n a t i o n s of n i t r o g e n . A p l o t of t h e e m i s s i o n s p e c t r u m i n t h e i m m e d i a t e r e g i o n o f t h i s l i n e i s p r o v i d e d i n F i g . 8. The 821.6 nm l i n e i s a b o u t h a l f as i n t e n s e as t h e 868.0 nm l i n e . F o r s u l p h u r , t h e 921.3 nm l i n e was f o u n d most i n t e n s e , a g a i n i n a g r e e m e n t w i t h F r y [ 2 8 ] , a n d was u s e d f o r q u a n t i t a t i v e d e t e r m i n a t i o n s . An e m i s s i o n s p e c t r u m between 905 nm and 932 nm i s g i v e n i n F i g u r e 9. The SI 922.8 nm l i n e i s p a r t i a l l y o v e r l a p p e d w i t h t h e A r l 922.5 nm l i n e w i t h our e x p e r i m e n t a l s y s t e m , but as shown i n F i g . 9, t h e s u b t r a c t i o n of a s p e c t r u m f r o m pure x y l e n e makes t h i s l i n e v i s i b l e . I t s h o u l d be n o t e d , t h a t under t h e c o n d i t i o n s o f low r f i n p u t p o w e r , h i g h n e b u l i z e r f l o w r a t e and l o w v i e w i n g h e i g h t , t h e C ^ - P h i l l i p s band ( s t r e t c h i n g f r o m about 875 t o 960 nm) was o b s e r v e d [ 5 7 ] . H o w e v e r , t h e e f f e c t o f t h i s band e m i s s i o n was n o t s i g n i f i c a n t u n d e r t h e w o r k i n g c o n d i t i o n s a d o p t e d f o r a n a l y s i s . No o t h e r s p e c t r a l i n t e r f e r e n c e f r o m m o l e c u l a r band e m i s s i o n w i t h any of t h e a n a l y t i c a l l i n e s was 32 f o u n d . F i g u r e 6. E m i s s i o n S p e c t r u m a t 777 nm. A e r o s o l : X y l e n e w i t h 1 % 0 added as I s o p r o p a n o l . I n t e g r a t i o n t i m e : 750 ms. D a r k c u r r e n t was s u b t r a c t e d . 33 a CN oo 5 A o vD 00 0> CO M z CN 00 CN vO 00 00 O CO vO • • • 00 00 00 vO \D vO 00 00 00 z z z 00 1-1 < en CN CT\ • • • O r-H r H r - r-» r-» oo oo oo M H A z z z L a 8 4 8 8 8 0 WAVELENGTH (NM) F i g u r e 7. E m i s s i o n s p e c t r u m a t 865 nm. A e r o s o l : X y l e n e w i t h 1 % N added as t r i e t h y l a m i n e . I n t e g r a t i o n t i m e : 1.5 s. D a r k c u r r e n t was s u b t r a c t e d . 34 8 0 3 8 3 3 WAVELENGTH (NM) F i g u r e 8. E m i s s i o n s p e c t r u m a t 820 nm. A e r o s o l : X y l e n e w i t h 1 % N added as t r i e t h y l a m i n e . I n t e g r a t i o n t i m e 1.5 s. D a r k c u r r e n t s u b t r a c t e d . 35 m oo cr\ i n vo vD r-» 00 CJ> O O O O O o> » 1^  » * Lil c: T 332 905 WAVELENGTH (NM) F i g u r e 9. E m i s s i o n s p e c t r a a t 920 nm. I n t . time 750 ms. A: A e r o s o l : X y l e n e w i t h 1 % S a d d e d a s d i p h e n y l -d i s u l f i d e . D a r k c u r r e n t s u b t r a c t e d . B: A e r o s o l : X y l e n e . D a r k c u r r e n t s u b t r a c t e d . C: S p e c t r u m B s u b t r a c t e d f r o m A, s h o w i n g t h e p a r t i a l l y o v e r l a p p e d SI 922.8 nm l i n e . 36 3.2 PHYSICAL APPEARANCE OF THE "XYLENE-PLASMA" When x y l e n e or any o t h e r o r g a n i c s o l v e n t i s a s p i r a t e d , t h e a p p e a r a n c e o f t h e p l a s m a changes d r a m a t i c a l l y compared t o t h e a q u e o u s p l a s m a . An o r g a n i c p l a s m a i s d e p i c t e d s c h e m a t i c a l l y i n F i g u r e 10. I n t e n s e g r e e n e m i s s i o n due t o t h e Q>2 Swan band a t 515 nm i s v i s i b l e a r o u n d t h e b o t t o m o f t h e p l a s m a , on t h e s i d e s up t o t h e t o r c h r i m and a l s o i n t h e a e r o s o l c h a n n e l j u s t above the n e b u l i z e r t u b e . The l e n g t h of t h i s c o r e o f g r e e n e m i s s i o n i n t h e c e n t r a l c h a n n e l i n c r e a s e s w i t h n e b u l i z e r f l o w r a t e and a l s o when s o l v e n t s , w h i c h a r e more v o l a t i l e t h a n x y l e n e , a r e a s p i r a t e d . F o r x y l e n e , t h e t i p o f t h i s g r e e n c o r e was j u s t a b o v e t h e l o a d c o i l f o r a n e b u l i z e r gas f l o w r a t e o f 0.4 1/min and a t 15 mm above the l o a d c o i l f o r 0.8 1 / m in. Above t h e t o r c h r i m , no g r e e n e m i s s i o n i s v i s i b l e on t h e o u t s i d e of t h e p l a s m a but v i o l e t e m i s s i o n due t o the CN v i o l e t s y s t e m a t 415 nm i s o b s e r v e d . T h i s s t r e t c h e s a l l a l o n g t h e p l a s m a and becomes more i n t e n s e on t h e t o p . 37 Violet Green F i g u r e 1 0 . T h e I C P w h e n x y l e n e i s a s p i r a t e d . 38 3.3 COMPLETENESS OF ATOMIZATION A t o m i z a t i o n o f o r g a n i c m o l e c u l e s i n t h e I C P i s o b v i o u s l y n o t c o m p l e t e . H o w e v e r , t h i s d o e s n o t i n t e r f e r e w i t h t h e d e t e r m i n a t i o n of a p a r t i c u l a r n o n m e t a l i f , e i t h e r t h e n o n m e t a l s o u g h t f o r i s not i n c o r p o r a t e d i n t h e m o l e c u l e s p r e s e n t ( i . e . a t o m i z a t i o n o f t h a t p a r t i c u l a r e l e m e n t i s c o m p l e t e ) , o r i f t h e o b s e r v e d a t o m i c e m i s s i o n o r i g i n a t e s f r o m a r e g i o n i n t h e p l a s m a where a t o m i z a t i o n i s c o m p l e t e . B o t h a s p e c t s , i . e . w h i c h m o l e c u l e s a r e p r e s e n t and t h e s p a t i a l dependance o f t h e c o m p l e t e n e s s o f a t o m i z a t i o n , were t h e r e f o r e e x a m i n e d . The o b v i o u s a v a i l a b l e t o o l was t h e e m i s s i o n f r o m m o l e c u l e s and t h e c o r r e s p o n d i n g atoms. S e v e r a l p o i n t s have t o be c o n s i d e r e d when i n t e r p r e t i n g e m i s s i o n d a t a f r o m t h a t p o i n t of v i e w . M o l e c u l e s w h i c h a r e p r e s e n t m i g h t not be d e t e c t e d by e m i s s i o n . S p a t i a l e m i s s i o n d a t a has t o be c o r r e l a t e d w i t h a measure f o r t h e t e m p e r a t u r e i n t h e p l a s m a . F u r t h e r , d i s a p p e a r a n c e o f e m i s s i o n f r o m n e u t r a l m o l e c u l e s m i g h t be c a u s e d by i o n i z a t i o n o f t h e s e t o p o s i t i v e l y c h a r g e d m o l e c u l e s . However, t h i s i s u n l i k e l y b e c a u s e t h e i o n i z a t i o n e n e r g i e s a r e g e n e r a l l y h i g h e r t h a n t h e d i s s o c i a t i o n e n e r g i e s . The d i a t o m i c s p e c i e s d e t e c t e d by t h e i r e m i s s i o n [ 3 6 ] and some o t h e r m o l e c u l e s l i k e l y t o be p r e s e n t a r e l i s t e d i n T a b l e I I a l o n g w i t h t h e i r d i s s o c i a t i o n and some i o n i z a t i o n e n e r g i e s . The i o n i z a t i o n e n e r g y o f Ar i s i n c l u d e d f o r 39 c o m p a r i s o n . TABLE I I D i s s o c i a t i o n and I o n i z a t i o n E n e r g i e s f o r some M o l e c u l e s M o l e c u l e D i s s o c i a t i o n E n e r g y (eV) I o n i z a t i o n E n e r g y (eV) ( A r ) 15.8 [58] CO 11.1 [21] 14.0 [59] N 2 9.8 [22] 15.6 [59] CN 8.2 [59] CS 7.6 [60] c 2 6.5 [60] NO 6.5 [60] °2 5.1 [21] 12.2 [59] OH 4.4 [60] CH 3.5 [47] 11.1 [59] 40 3.3.1 EMISSION FROM DIATOMIC MOLECULES The a c c e s s i b l e s p e c t r a l r a n g e f r o m about 200 nm t o 1000 nm was s e a r c h e d f o r m o l e c u l a r e m i s s i o n band s t r u c t u r e at s e v e r a l v i e w i n g h e i g h t s . F a i n t r i p p 1 e - s t r u c t u r e i n t h e b a c k g r o u n d o c c u r e d i n many s p e c t r a l r e g i o n s , but b e s i d e s the a l r e a d y m e n t i o n e d C 2 P h i l l i p s and Swan b a n d s and t h e CN v i o l e t band, no s t r o n g i d e n t i f i a b l e m o l e c u l a r e m i s s i o n bands w e r e f o u n d . The C 2 Swan band a t 515 nm and t h e CN v i o l e t band a t 415 nm a r e shown i n F i g u r e s 11 and 12. The o t h e r d i a t o m i c s p e c i e s r e p o r t e d by B o o r n and B r o w n e r [ 3 6 ] , CH, CS , OH a n d NO, c o u l d n o t be d e t e c t e d ( 5 0 % 1 , 3 -p r o p a n e d i t h i o 1 a d d e d t o x y l e n e and p u r e i s o p r o p a n o l w e r e a s p i r a t e d when s e a r c h i n g f o r CS and OH r e s p e c t i v e l y ) . These m o l e c u l e s m i g h t h a v e b e e n a b s e n t , b u t a n o t h e r e x p l a n a t i o n c o u l d be, t h a t a l l t h e s e b a n d s ( e x c e p t CH a t 430 nm) l i e i n a r e g i o n ( 2 0 0 - 400 nm) w h e r e t h e PDA i s r e l a t i v e l y i n s e n s i t i v e compared t o t h e PMT w h i c h Boorn and Browner used f o r t h e i r i n v e s t i g a t i o n s . T h e r e f o r e , t h i s d a t a i s n o t v e r y c o n c l u s i v e . 41 CM m ON m i—i m 490 525 WpVELENGTh C NM3 F i g u r e 11. C 2 Swan band a t 515 nm, I n t e g r a t i o n t i m e : 750 ms. A e r o s o l : X y l e n e 42 WAVELENGTH (NM) F i g u r e 12. CN V i o l e t band a t 415 nm. A e r o s o l : X y l I n t e g r a t i o n t i m e : 50 ms. 3.3.2 EMISSION PROFILES E x c i t a t i o n t e m p e r a t u r e p r o f i l e s a c q u i r e d f o r t h e x y l e n e p l a s m a by B l a d e s and C a u g h l i n [49] a r e r e p r o d u c e d i n F i g u r e 13 b e c a u s e a q u a l i t a t i v e p i c t u r e o f t h e t e m p e r a t u r e d i s t r i b u t i o n i n t h e ICP w i l l be needed f o r t h e d i s c u s s i o n of t h e s u b s e q u e n t l y p r e s e n t e d p r o f i l e s . D a t a f o r 2 kW, t h e i n p u t p o w e r l e v e l u s e d t h r o u g h o u t t h i s work, was n o t o b t a i n e d by B l a d e s and C a u g h l i n , b u t t h e r e s h o u l d n o t be a s u b s t a n t i a l d i f f e r e n c e t o t h e 1.25 and 1.75 kW p l a s m a . Two main r e g i o n s can be d i s t i n g u i s h e d : a t o r o i d a l r e g i o n above t h e i n d u c t i o n z o n e and an a x i a l r e g i o n . I n t h e t o r o i d a l r e g i o n , t h e t e m p e r a t u r e i s h i g h a t low h e i g h t s and d e c r e a s e s w i t h i n c r e a s i n g h e i g h t . In t h e a x i a l r e g i o n t h e t e m p e r a t u r e i s g e n e r a l l y l o w e r t h a n i n t h e t o r o i d a l r e g i o n but i n c r e a s e s w i t h h e i g h t . T e m p e r a t u r e p r o f i l e s b e l o w 10 mm w e r e n o t a c q u i r e d , b u t t h e i n d i c a t e d t r e n d s c a n be e x p e c t e d t o be more p r o n o u n c e d a t l o w e r h e i g h t s . 44 7000 E00O 5000 c r a. s: LU 4000 3000 7000 E000 5000 c r LU 4000 SOOO 8 6 4 2 0 2 4 6 8 • I STRNCE FROM PX IS (MM) 8 6 4 2 0 2 4 E S D ISTPNCE FROM PX IS (MM) 7000 EOOO 5000 L U £ £ I — c r LU a. z: LU 4000 3000 iii 8 E 4 2 0 2 4 E 8 DISTPNCE FROM PX IS (MM) F i g u r e 13. F e l E x c i t a t i o n T e m p e r a t u r e p r o f i l e s of t h e ICP when x y l e n e i s a s p i r a t e d , a: 1.75 kW, b: 1.25 kW. ( i ) 10mm, ( i i ) 15 mm and ( i i i ) 20 mm from t h e l o a d c o i l . T aken from B l a d e s and C a u g h l i n [ 4 9 ] , The f o l l o w i n g p r o f i l e s w e r e a l l a c q u i r e d a b o v e t h e t o r c h r i m , w h i c h was l o c a t e d 4 - 5 mm a b o v e t h e l o a d c o i l . The n e b u l i z e r g a s f l o w r a t e was a d j u s t e d t o 0.70 1 /min, so t h a t t h e t i p o f t h e g r e e n C 2 c o r e was v i s i b l e 2 mm a b o v e t h e t o r c h r i m a n d t h a t i n f l u e n c e c o u l d s h o w up i n t h e measurements. The w a v e l e n g t h s and i n t e g r a t i o n t i m e s u s e d f o r t h e a c q u i s i t i o n o f t h e p r e s e n t e d p r o f i l e s a r e p r o v i d e d i n T a b l e I I I . A l l p r o f i l e s w e r e c o r r e c t e d f o r v a r i a t i o n s i n t h e b a c k g r o u n d by m e a s u r i n g i t s i n t e n s i t y c l o s e t o t h e a n a l y t e l i n e and s u b t r a c t i n g t h a t v a l u e . The v i e w i n g h e i g h t s , w i t h t h e t o p o f t h e l o a d c o i l as t h e r e f e r e n c e p o i n t , a r e i n d i c a t e d i n t h e p r o f i l e s . TABLE I I I E x p e r i m e n t a l C o n d i t i o n s f o r t h e A c q u i s i t i o n o f t h e P r o f i l e s S p e c i e s W a v e l e n g t h PDA I n t e g r a t i o n Time C 2 516.5 nm 50 ms ( F i g . 14) 250 ms ( F i g . 26) CN 421.6 nm 250 ms CI 907.8 nm 150 ms SI 921.3 nm 1500 ms 01 777.5 nm 1000 ms 46 3.3.2.1 C 2 AND CN EMISSION PROFILES L a t e r a l e m i s s i o n p r o f i l e s o f C 2 a r e g i v e n i n F i g u r e 14. E m i s s i o n f r o m C 2 i s l i m i t e d t o t h e c e n t r a l c h a n n e l and t h e p r o f i l e s a g r e e w i t h t h e v i s u a l l y o b s e r v e d e x t e n t o f C 2 e m i s s i o n . The p l o t s o f CN e m i s s i o n ( F i g u r e s 15, 16 and 17) show some CN i n t h e c e n t r a l c h a n n e l a t l o w h e i g h t s , w h i c h p r o b a b l y i s due t o n i t r o g e n i m p u r i t i e s i n t h e x y l e n e and a r g o n s u p p l y . S t r o n g CN e m i s s i o n i s f o r m e d on t h e o u t e r l a y e r s o f t h e ICP w h i c h must be c a u s e d by n i t r o g e n e n t r a i n e d f r o m t h e s u r r o u n d i n g a i r . T h i s e m i s s i o n e x t e n d s a c r o s s t h e w i d t h o f t h e p l a s m a a t l a r g e r h e i g h t s . A d d i n g p y r i d i n e t o x y l e n e ( a p p r o x i m a t e l y 10 %) c a u s e s h i g h CN e m i s s i o n i n t e n s i t i e s i n t h e c e n t r a l c h a n n e l a t l o w h e i g h t s , w h i c h must o r i g i n a t e f r o m t h e sample ( F i g u r e 18). 47 CZ 5MM L C2 7MM <_ CO 10 10 > I — c r _ J L U or 10 0 E 4 2 0 2 4 G B 1 0 DISTANCE FROM RXIS (MM) A . 10 8 6 4 2 0 2 4 E 8 10 DISTPNCE FROM RXIS (MM) C2 9MM l_ > t— c r _ i L U 10 8 E 4 2 0 2 4 G 8 10 DISTANCE FROM RXIS (MM) F i g u r e 14. L a t e r a l C 2 e m i s s i o n p r o f i l e s . CN 5MM CN 7MM co to > i— cr _ i U J i n 10 8 6 4 2 0 2 4 6 8 10 DISTANCE FROM PX IS (MM) co co U J A A 10 8 6 4 2 0 2 4 E 8 10 DISTANCE FROM AXIS (MM) CN 9MM CN 11MM 10 8 G 4 2 0 2 4 G 8 10 10 8 E 4 2 0 2 4 S 8 10 DISTANCE FROM PX IS (MM) D ISTANCE FROM AX IS (MM) F i g u r e 15. R a d i a l CN e m i s s i o n p r o f i l e s ( 1) CN 15MM T- lJj f tHI«-10 8 E 4 2 0 2 4 S 8 10 DISTANCE FROM AXIS (MM) CN 20MM CO co > I — c r _ i U J m 10 8 6 4 2 0 2 4 6 8 10 DISTANCE FROM AXIS (MM) F i g u r e 16. R a d i a l CN e m i s s i o n p r o f i l e s ( 2) CN 35MM CN 40MM F i g u r e 17. R a d i a l CN e m i s s i o n p r o f i l e s (3) CN 5MM P CN 7MM P -A- 11 10 8 6 4 2 0 2 4 6 8 10 DISTANCE FROM AX IS (MM) co CO > t— c r _ i L U DC 10 8 6 4 2 0 2 4 6 8 10 DISTANCE FROM AXIS (MM) CN 9MM P CN 11MM P 10 8 6 4 2 0 2 4 6 8 10 10 8 6 4 2 0 2 4 6 8 10 DISTANCE FROM AXIS (MM) D ISTANCE FROM AX IS (MM) F i g u r e 18. R a d i a l CN e m i s s i o n p r o f i l e s when 10 % p y r i d i n e added. 3.3.2.2 CI AND SI EMISSION PROFILES The p r o f i l e s o f CI e m i s s i o n i n F i g u r e s 19 and 20 and of SI e m i s s i o n i n F i g u r e s 21 and 22 ( 2 0 % d i m e t h y l s u l f o x i d e i n x y l e n e ) show e m i s s i o n f r o m t h e t o r o i d a l r e g i o n o f t h e p l a s m a a t a l l h e i g h t s . In t h e c e n t r a l c h a n n e l , e m i s s i o n i n t e n s i t i e s a r e weak low i n t h e p l a s m a and i n c r e a s e w i t h h e i g h t . 53 RELATIVE EMISSION INTENSITY F i g u r e 2 0 . R a d i a l CI e m i s s i o n p r o f i l e s (2 ) SI 5MM SI 7MM in in in in 10 8 6 4 2 0 2 4 6 8 10 DISTANCE FROM AXIS (MM) 10 8 6 4 2 0 2 4 6 8 10 DISTANCE FROM AXIS (MM) SI 9MM SI 11MM in in c r L U 10 8 6 4 2 0 2 4 6 8 10 DISTANCE FROM AXIS (MM) in in L U U J 10 8 6 4 2 0 2 4 6 8 10 DISTANCE FROM PX IS (MM) F i g u r e 2 1 . R a d i a l S I e m i s s i o n p r o f i l e s ( 1 ) 56 SI 15MM SI 20MM F i g u r e 22 . R a d i a l SI e m i s s i o n p r o f i l e s (2 ) 57 3 . 3 . 3 . CONCLUSIONS E m i s s i o n f r o m m o l e c u l a r s p e c i e s o r i g i n a t i n g f r o m t h e s a m p l e , C 2 and CN f r o m p y r i d i n e , was o b s e r v e d l o w i n t h e c e n t r a l c h a n n e l but d i s a p p e a r e d w i t h i n c r e a s i n g h e i g h t . T h i s a g r e e s w i t h t h e v i s u a l l y o b s e r v e d e x t e n t o f t h e g r e e n c o r e of C 2 e m i s s i o n . The f a c t t h a t t h e s t r o n g m o l e c u l e CN w i t h a d i s s o c i a t i o n e n e r g y o f 8.2 eV, d i s a p p e a r e d i n t h e c e n t r a l c h a n n e l a b o v e t h i s h e i g h t s u g g e s t s , t h a t a t o m i z a t i o n i s c o m p l e t e above a c e r t a i n h e i g h t i n t h e a e r o s o l c h a n n e l . The h e i g h t w h e r e t h i s i s a c h i e v e d , p r e s u m a b l y d e p e n d s on t h e n e b u l i z e r g a s f l o w r a t e , a s t h e l e n g t h o f t h e v i s i b l e C 2 c o r e changes. The p r o f i l e s o f a t o m i c e m i s s i o n o f CI and SI s h o w i n g low i n t e n s i t i e s low i n t h e c e n t r a l c h a n n e l , comply w e l l w i t h the e x t e n t o f m o l e c u l a r e m i s s i o n . The o c c u r a n c e o f e m i s s i o n f r o m CI and SI i n t h e l o w t o r o i d a l r e g i o n o f t h e p l a s m a i n d i c a t e s , t h a t t h e s a m p l e d i f f u s e s v e r y r a p i d l y s i d e w a y s f r o m t h e a e r o s o l c h a n n e l . The f a c t , t h a t a t low h e i g h t s , where a t o m i z a t i o n i n the c e n t r a l c h a n n e l i s not c o m p l e t e , most of t h e a t o m i c e m i s s i o n o r i g i n a t e s f r o m t h e t o r o i d a l r e g i o n , i m p l i e s , t h a t an i n t e r f e r e n c e f r o m i n c o m p l e t e a t o m i z a t i o n i s s m a l l and i n d e p e n d e n t of v i e w i n g h e i g h t . 58 3.4 OPTIMIZATION 3.4.1 ENTRAINMENT OF AIR 01 e m i s s i o n p r o f i l e s t a k e n a t f o u r h e i g h t s a r e g i v e n i n F i g u r e 23. O x y g e n i s o b s e r v e d a t t h e o u t e r l a y e r s o f t h e p l a s m a , r i g h t a t t h e t o r c h r i m (5 mm). W i t h i n c r e a s i n g h e i g h t , more and more o x y g e n h a s b e e n e n t r a i n e d and h a s t r a v e l l e d f u r t h e r t o w a r d s the c e n t r e . 3.4.2 EXCLUSION OF AIR A f i r s t a t t e m p t t o e l i m i n a t e t h i s e n t r a i n m e n t was made by s i m p l y p l a c i n g a s h o r t p i e c e o f q u a r t z t u b e on t o p o f t h e t o r c h . I t was f o u n d t h a t t h i s c r u d e d e v i c e was n o t e f f i c i e n t f o r t h e e x c l u s i o n o f a i r and a l s o b l a c k e n e d v e r y r a p i d l y w i t h c a r b o n d e p o s i t s when a s p i r a t i n g x y l e n e , making t h e o b s e r v a t i o n o f a n a l y t e l i n e s i m p o s s i b l e . D i f f e r e n t s hapes and s i z e s o f "add-on" e x t e n s i o n s were t h e n t e s t e d t o d e t e r m i n e w h e t h e r t h e d e p o s i t i o n o f c a r b o n c o u l d be p r e v e n t e d . I t was f o u n d t h a t s u c h a t o r c h e x t e n s i o n had t o be s e a l e d v e r y c a r e f u l l y t o t h e t o r c h i n o r d e r t o c o m p l e t e l y e x c l u d e any oxygen. F i g u r e 24 i s a s c h e m a t i c d r a w i n g s h o w i n g how t h e e x t e n s i o n s w e r e c o n n e c t e d t o t h e t o r c h . T h e e x t e n s i o n shown i n F i g . 24 i s a s t r a i g h t b o r e q u a r t z t u b e . W i t h t h a t e x t e n s i o n i n p l a c e t h e p l a s m a changes i t s 59 F i g u r e 23. R a d i a l 01 e m i s s i o n p r o f i l e s . o o o - 5 — 4 2 J •3 F i g u r e 24. T o r c h and c o n n e c t o r shown w i t h s t r a i g h t t u b e e x t e n s i o n i n c r o s s s e c t i o n a l v i e w . 1. S t r a i g h t t u b e e x t e n s i o n . 2. T o r c h . 3. C o n n e c t o r ( T e f l o n ) w i t h r u b b e r 0-r i n g s . 4. L o a d C o i l . 5. P l a s m a a s d e p i c t e d by i t s e n v e l o p e o f g r e e n Co e m i s s i o n . 6. T o r c h h o l d e r . 7. B o r e f o r a d d i t i o n a l s n e a t h i n g a r g o n ( s e e t e x t ) . D i m e n s i o n s : A: 25.5 mm B: 22 mm C: 150 mm D: 20.37 mm. 61 a p p e a r a n c e . The v i s i b l e t a i l p l u m e n o r m a l l y o n l y about 3 - 4 cm h i g h p e r s i s t s up t o a b o u t 1 cm b e y o n d t h e t o p o f t h e e x t e n s i o n . G r e e n e m i s s i o n c a u s e d by C 2 i s no l o n g e r r e s t r i c t e d t o b e l o w t h e t o r c h r i m b u t e x t e n d s t o t h e t o p o f t h e e x t e n s i o n . V i o l e t CN e m i s s i o n i s no l o n g e r o b s e r v e d . A l t h o u g h t h e p l a s m a c h a n g e s i t s a p p e a r a n c e w i t h t h e e x t e n s i o n , i t was f o u n d t h a t i t s e x c i t a t i o n c h a r a c t e r i s t i c s d i d n o t c h a n g e s i g n i f i c a n t l y . An e x a c t , s p a t i a l l y r e s o l v e d e v a l u a t i o n , however, i s n o t p o s s i b l e b e c a u s e t h e e x t e n s i o n a l t e r s o p t i c a l c h a r a c t e r i s t i c s . The s t r a i g h t t u b e e x t e n s i o n o f F i g . 2 4 was f o u n d t o be v e r y e f f e c t i v e f o r t h e e x c l u s i o n o f a t m o s p h e r i c g a s e s . H o w e v e r , i t i s v e r y s u s c e p t i b l e t o t h e b u i l d u p o f c a r b o n d e p o s i t s . When a s p i r a t i n g x y l e n e , t h e e x t e n s i o n t e n d s t o b l a c k e n a t a b o u t t h r e e cm a b o v e t h e l o a d c o i l w i t h i n a few m i n u t e s . A f t e r i n i t i a l f o r m a t i o n , t h e c a r b o n d e p o s i t s s p r e a d upwards and downwards, e v e n t u a l l y c o a t i n g t h e e n t i r e t u b e . The d i f f e r e n t e x t e n s i o n s w h i c h were t r i e d a r e d e p i c t e d i n F i g . 25. R e m o v i n g t h e w a l l f r o m t h e p l a s m a a s i n F i g s . 25a and 25b c a u s e s t h e p l a s m a t o f l i c k e r b a d l y and o x y g e n e x c l u s i o n i s not c o m p l e t e . N a r r o w i n g t h e top as i n F i g . 25c made t h e e x t e n s i o n e f f i c i e n t , b u t t h e w a l l g o t b l a c k e n e d v e r y r a p i d l y . The s o l u t i o n f i n a l l y a r r i v e d a t , was t o u s e t h e s t r a i g h t t u b e a s e x t e n s i o n and t o i s o l a t e t h e p l a s m a f r o m t h e w a l l o f t h e e x t e n s i o n by i n t r o d u c i n g a r g o n 62 A C \ / - B -F i g u r e 25. C r o s s s e c t i o n a l v i e w o f t o r c h e x t e n s i o n s . D i m e n s i o n s : A: 22 mm B: 25.5 mm C:45 mm D: 70 mm E: 38 mm F: 150 mm G: 33 mm H: 45 mm 63 ( a p p r o x i m a t e l y 2 1/min) t a n g e n t i a l l y t h r o u g h a h o l e i n t h e c o n n e c t o r ( s e e F i g . 24) i n t o t h e gap b e t w e e n t o r c h and e x t e n s i o n . T h i s a r r a n g e m e n t k e e p s t h e l o w e r h a l f o f t h e e x t e n s i o n f r e e o f c a r b o n d e p o s i t s when a s p i r a t i n g x y l e n e . No p r o b l e m s i n o p e r a t i o n o c c u r e d , a l t h o u g h o c c a s i o n a l s p u t t e r i n g o f t h e p l a s m a was o b s e r v e d . The r e a s o n f o r t h i s c o u l d n o t be f o u n d . F i g 26. s h o w s r a d i a l p r o f i l e s o f C2 a c q u i r e d w i t h t h a t s e t up s h o w i n g C2 a t l o c a t i o n s where not n o r m a l l y p r e s e n t . The p r e s e n c e o f C2 c l o s e t o t h e w a l l o f t h e e x t e n s i o n e x p l a i n s a l s o t h e s e n s i t i v i t y o f i t t o s o o t b u i l d up s i n c e an o t h e r d i c a r b o n m o l e c u l e , a c e t y l e n e , i s f o u n d t o be a m a j o r p r e c u r s o r f o r t h e f o r m a t i o n o f s o o t [ 6 0 ] . 3 . 4 . 3 AMBIENT OXYGEN AND NITROGEN O x y g e n and n i t r o g e n e m i s s i o n was o b s e r v e d e v e n i n t h e pure a r g o n p l a s m a , when e n t r a i n m e n t of a t m o s p h e r i c g a s e s was p r e v e n t e d , so t h o s e e l e m e n t s must be p r e s e n t as i m p u r i t i e s i n t h e a r g o n t a n k s . T h e s e a m o u n t s w e r e f o u n d t o v a r y a s d i f f e r e n t t a n k s w e r e u s e d . I t was a l s o f o u n d , t h a t x y l e n e , e v e n o f s p e c t r o s c o p i c g r a d e , c o n t a i n s o x y g e n i n some f o r m . T r e a t m e n t w i t h m o l e c u l a r s i e v e s (3 A) and b u b b l i n g n i t r o g e n t h r o u g h t h e s o l v e n t f o r s e v e r a l h o u r s r e d u c e t h i s o x y g e n c o n t a m i n a t i o n e f f e c t i v e l y , so t h a t t h i s c o n t r i b u t i o n i s 64 C2 5MM EX C2 10MM EX C2 15MM EX CO CO 10 8 6 4 2 0 2 4 G B 10 DISTANCE FROM AXIS (MM) F i g u r e 26. R a d i a l C 2 e m i s s i o n p r o f i l e s w i t h s t r a i g h t t u b e e x t e n s i o n i n p l a c e . 65 s m a l l compared t o t h e amount f o u n d i n t h e pure a r g o n p l a s m a i t s e l f . T h e r e f o r e a l l x y l e n e u s e d f o r t h e s u b s e q u e n t d e t e r m i n a t i o n s was t r e a t e d t h a t way. No i n c r e a s e i n a m b i e n t n i t r o g e n e m i s s i o n c o u l d be d e t e c t e d when x y l e n e was a s p i r a t e d . 3 . 4 . 4 OPERATING CONDITIONS AND VIEWING REGION Rf i n p u t power, gas f l o w r a t e s and v i e w i n g h e i g h t were o p t i m i z e d f o r maximum i n t e n s i t y w i t h t h e a d o p t e d e x t e n s i o n i n p l a c e . - Rf i n p u t p o w e r : E m i s s i o n i n t e n s i t i e s w e r e f o u n d t o i n c r e a s e s t r o n g l y w i t h l o a d power, t h e r e f o r e i t was l e f t a t t h e o r i g i n a l 2 kW. - P l a s m a a n d a u x i l i a r y a r g o n f l o w : B o t h f l o w r a t e s d i d n o t i n f l u e n c e t h e e m i s s i o n i n t e n s i t y s i g n i f i c a n t l y and were l e f t a t t h e o r i g i n a l 12 and 2 1/min. - N e b u l i z e r a r g o n f l o w r a t e and v i e w i n g a r e a : B e c a u s e t h e t i p o f t h e g r e e n C 2 c o r e i n t h e n e b u l i z e r c h a n n e l r i s e s w i t h n e b u l i z e r a r g o n f l o w r a t e i t was e x p e c t e d , t h a t t h e n e b u l i z e r g a s f l o w r a t e a n d v i e w i n g h e i g h t w o u l d be i n t e r d e p e n d e n t . E m i s s i o n i n t e n s i t i e s v e r s u s v i e w i n g h e i g h t a l o n g t h e c e n t e r of t h e p l a s m a were t h e r e f o r e a c q u i r e d f o r s e v e r a l n e b u l i z e r gas f l o w r a t e s . V e r t i c a l oxygen e m i s s i o n i n t e n s i t y p r o f i l e s a r e g i v e n i n F i g u r e 27. T h e p e a k 66 i n t e n s i t y was f o u n d a t a v i e w i n g h e i g h t o f 3 mm f o r a l l f l o w r a t e s e x e p t 0.4 l / m i n . A f l o w r a t e o f 0.5 l / m i n gave maximum p e a k e m i s s i o n i n t e n s i t y . A s i m i l a r p l o t f o r s u l p h u r ( F i g . 28) shows h i g h e s t e m i s s i o n i n t e n s i t y f o r a somewhat h i g h e r v i e w i n g h e i g h t and n e b u l i z e r g a s f l o w r a t e . A q u i c k s u r v e y f o r n i t r o g e n s u g g e s t e d , t h a t t h e b e s t v i e w i n g h e i g h t f o r t h a t e l e m e n t i s a l s o f o u n d i n t h e r e g i o n o f a few mm a b o v e the l o a d c o i l . B e c a u s e t h e r a d i a l i n t e n s i t y p r o f i l e s ( s e c t i o n 3.3.2.2) s u g g e s t , t h a t most n o n m e t a l e m i s s i o n a t low h e i g h t s does not o r i g i n a t e f r o m t h e c e n t r a l c h a n n e l , l a t e r a l p r o f i l e s o f SI e m i s s i o n i n t e n s i t y were o b t a i n e d ( F i g 29) t o che c k whether o b s e r v a t i o n o f f t h e c e n t r a l a x i s was d e s i r a b l e . O n l y a s l i g h t d i p a t 5 mm was f o u n d , and o b s e r v a t i o n was made a t the c e n t r e . 67 I 1 1 1 I I I I I I I 0 3 6 9 12 15 18 21 24 27 30 Height Above Loadcoil (mm) F i g u r e 27. O x y g e n e m i s s i o n i n t e n s i t i e s a l o n g t h e c e n t r a l a x i s when x y l e n e mixed w i t h o c t a n o l (1 % oxygen) a s p i r a t e d . S t r a i g h t tube e x t e n s i o n i n p l a c e . F o u r d i f f e r e n t n e b u l i z e r gas f l o w r a t e s were employed. • - 0.4 l / m i n A - 0.5 l / m i n • - 0.6 l / m i n x - 0.7 l / m i n 68 Height Above Load Coil (mm) F i g u r e 28. S u l p h u r e m i s s i o n i n t e n s i t i e s a l o n g t h e c e n t r a l a x i s when d i p h e n y l d i s u l f i d e i n x y l e n e ( 1 % s u l p h u r ) a s p i r a t e d . F i v e d i f f e r e n t n e b u l i z e r f l o w r a t e s were employed. A- 0.4 l / m i n 0 ~ 0.5 l / m i n 0.6 l / m i n ^ - 0.7 l / m i n A ' - 0.8 l / m i n 69 F i g u r e 29. L a t e r a l SI e m i s s i o n p r o f i l e s . 70 3.4 .5 . CONTROLLED SAMPLE DELIVERY T h e u s e o f a pump t o c o n t r o l s a m p l e f l o w t o t h e n e b u l i z e r was a t t e m p t e d . T h i s p r o m i s e s t o r e d u c e i n t e r f e r e n c e e f f e c t s due t o i n c o n s i s t e n t d e l i v e r y r a t e s b e c a u s e o f d i f f e r e n t p h y s i c a l p r o p e r t i e s o f s a m p l e s ( e s p e c i a l l y v i s c o s i t y ) and a l l o w s an o p t i m i z a t i o n of sample d e l i v e r y r a t e ( a n d n e b u l i z e r e f f i c i e n c y ) i n d e p e n d e n t f r o m the n e b u l i z e r gas f l o w r a t e . S i g n a l i n t e n s i t i e s were f o u n d t o i n c r e a s e s t r o n g l y w i t h d e l i v e r y r a t e . At r e l a t i v e l y h i g h d e l i v e r y r a t e s (up t o 3 m l / m i n ) t h e t i m e t o r e a c h a s t a b l e s i g n a l a f t e r c h a n g i n g a s a m p l e b e c a m e v e r y l o n g ( a p p r o x i m a t e l y 5 m i n ) due t o memory e f f e c t s i n t h e s p r a y c h a m b e r . I t was a l s o f o u n d , t h a t t h e c a p i l l a r y t i p s o f c o n c e n t r i c n e b u l i z e r s t e n d t o g e t damaged when f o r c e - f e d a t r a t e s g r e a t e r t h a n t h e f r e e u p t a k e r a t e . F o r t h e s e r e a s o n s c o n t r o l l e d s a m ple f e e d was not g e n e r a l l y employed. 3.4.6. CONCLUSIONS The t o r c h e x t e n s i o n a l l o w e d us t o e s t a b l i s h an o p t i m a l v i e w i n g h e i g h t f o r o x y g e n and t o e v a l u a t e t h e e x t e n t and s p a t i a l dependance o f e n t r a i n m e n t o f a t m o s p h e r i c g a s e s and t o d i s t i n g u i s h a m b i e n t o x y g e n and n i t r o g e n i n t h e s o l v e n t and a r g o n s u p p l y . C o m p r o m i s e o p e r a t i n g c o n d i t i o n s a d o p t e d f o r t h e 7 1 d e t e r m i n a t i o n o f t h e t h r e e e l e m e n t s were: r f i n p u t power 2 kW, p l a s m a g a s f l o w . r a t e 12 l / m i n , and a u x i l i a r y g a s f l o w r a t e 2 l / m i n . The n e b u l i z e r g a s f l o w r a t e was s e t t o 0.5 l / m i n . The v i s i b l e C 2 c o r e e x t e n d s t o a b o u t 2 mm a b o v e t h e l o a d c o i l f o r t h i s f l o w r a t e . The s u l p h u r l i n e was u s u a l l y m e a s u r e d 6 mm a b o v e t h e l o a d c o i l and t h e o x y g e n and n i t r o g e n l i n e s 3 mm above t h e l o a d c o i l , w h i c h was 2 mm below the t o r c h r i m . D e t e r m i n a t i o n o f oxygen and n i t r o g e n c o u l d be done w i t h o u t t h e t o r c h e x t e n s i o n , b e c a u s e t h e b e s t v i e w i n g h e i g h t f o r t h e s e e l e m e n t s was f o u n d b e l o w t h e t o r c h r i m , where t h e r e i s no i n t e r f e r e n c e f r o m t h e a t m o s p h e r e . The f a c t t h a t t h e peak e m i s s i o n i n t e n s i t i e s o f t h e two n o n m e t a l s w e r e f o u n d l o w i n v i e w i n g h e i g h t o r i g i n a t i n g m o s t l y f r o m t h e t o r o i d a l r e g i o n , as shown i n s e c t i o n 3.3.2.2 f o r s u l p h u r , a g r e e s w e l l w i t h d a t a p r e s e n t e d f o r o t h e r n e u t r a l h i g h e n e r g y e m i s s i o n l i n e s [ 6 2 ] , An e x p l a n a t i o n i s a t t e m p t e d as f o l l o w s . I o n i z a t i o n o f t h e n o n m e t a l s i s u n l i k e l y , b e c a u s e o f t h e i r h i g h i o n i z a t i o n e n e r g i e s , and no e m i s s i o n f r o m i o n i c 0, N o r S h a s b e e n d e t e c t e d f o r t h e A r - I C P [ 2 1 , 2 2 , 2 8 ] . T h e r e f o r e , t h e d e c r e a s e o f n o n m e t a l e m i s s i o n i n t e n s i t y w i t h v i e w i n g h e i g h t above t h e h e i g h t of peak i n t e n s i t y c a n n o t be c a u s e d by g r a d u a l i o n i z a t i o n , b u t m u s t be d u e t o a d e c r e a s i n g f r a c t i o n o f t h e n o n m e t a l b e i n g e x c i t e d . T h i s 72 a g r e e s w i t h t h e f a c t , t h a t i n t h e t o r o i d a l r e g i o n , w h e r e m o s t o f t h e n o n m e t a l e m i s s i o n o r i g i n a t e s , t h e e x c i t a t i o n t e m p e r a t u r e d e c r e a s e s w i t h h e i g h t . The o p t i m a l v i e w i n g h e i g h t i s p r o b a b l y d e t e r m i n e d by two mechanisms w h i c h c o u n t e r a c t each o t h e r . W i t h i n c r e a s i n g h e i g h t more and more o f t h e a n a l y t e d i f f u s e s i n t o t h e h o t t o r o i d a l r e g i o n where i t can g e t e x c i t e d t o t h e upper s t a t e l e v e l o f t h e n e a r IR e m i s s i o n l i n e . T he t e m p e r a t u r e i n t h e t o r o i d a l r e g i o n h o w e v e r d e c r e a s e s s t e a d i l y w i t h h e i g h t so t h a t t h e f r a c t i o n o f p r e s e n t a n a l y t e s p e c i e s w h i c h g e t s e x c i t e d d e c r e a s e s as w e l l . T h i s d o e s e x p l a i n as w e l l , why t h e b e s t v i e w i n g h e i g h t f o r s u l p h u r i s h i g h e r t h a n f o r oxygen b e c a u s e o f t h e l o w e r upper s t a t e l e v e l and t h e r e f o r e h i g h e r f r a c t i o n o f s u l p h u r w h i c h i s p r e s u m a b l y e x c i t e d . 73 3.5 ANALYTICAL PERFORMANCE 3.5.1 RESPONSE FROM DIFFERENT COMPOUNDS Whether t h e n o n m e t a l e m i s s i o n i n t e n s i t y was dependent on t h e s a m p l e c o m p o s i t i o n was i n v e s t i g a t e d by c o m p a r i n g t h e r e s p o n s e o f a s e r i e s o f s o l u t i o n s a l l of w h i c h c o n t a i n e d t h e same a m o u n t o f t h e n o n m e t a l b u t i n f o r m o f a d i f f e r e n t compound. S o l u t i o n s c o n t a i n i n g 1 % oxygen, 3 % n i t r o g e n or 1 % s u l p h u r i n x y l e n e w e r e t h u s p r e p a r e d and t h e r e s p e c t i v e n o n m e t a l e m i s s i o n i n t e n s i t y measured. I t was f o u n d t h a t when t h e s o l u t e s c o n t a i n i n g t h e n o n m e t a l , had b o i l i n g p o i n t s l o w e r t h a n 2 0 0 ° C , a d e p e n d e n c e on t h e v o l a t i l i t y o f t h e s e compounds was e x h i b i t e d . The n o n m e t a l e m i s s i o n i n t e n s i t y was h i g h e r , t h e l o w e r t h e b o i l i n g p o i n t o f t h e n o n m e t a l p a r e n t compound. 3.5.1.1 VOLATILE SOLUTES T a b l e I V g i v e s a l i s t o f t h e v o l a t i l e s o l u t e s c o n t a i n i n g t h e n o n m e t a l s w h i c h w e r e t e s t e d and t h e i r r e s p o n s e f a c t o r s . I n F i g . 30 t h e e m i s s i o n i n t e n s i t i e s o f t h e n o n m e t a l s a r e p l o t t e d as a f u n c t i o n o f t h e b o i l i n g p o i n t o f t h e p a r e n t compound. N o t e , t h a t t h e i n t e n s i t y s c a l e i s l o g a r i t h m i c , t h e r e f o r e t h i s e f f e c t i s v e r y p r o n o u n c e d , a d e c r e a s e o f 5 0 ° C i n b o i l i n g p o i n t c a u s e s r o u g h l y a 74 TABLE IV V o l a t i l e S o l u t e s Compound Oxygen c o n t a i n i n g compounds 01 D i m e t h y l s u l f o x i d e 02 2 - 0 c t a n o l 03 2 - 0 c t a n o n e 04 A c e t i c A c i d A n h y d r i d e 05 I s o p r o p a n o l 06 M e t h y l - e t h y 1 - k e t o n e 07 M e t h a n o l 08 A c e t o n e 51 D i m e t h y l s u l f o x i d e 52 1 , 3 - P r o p a n e d i t h i o l 53 S u l p h u r - I - c h l o r i d e 54 T e t r a h y d r o t h i o p h e n e B.P. R e l a t i v e (°C) Response as 1 % 0 i n x y l e n e 189 1.5 177 1.4 170 1.8 139 3.3 82 36 80 21 65 71 56 43 .5 .5 .8 .6 .3 .8 189 1.14 169 1.07 138 1.8 119 2.6 N i t r o g e n c o n t a i n i n g compounds as 3 % N i n x y l e n e N l D i - n - h e x y l a m i n e 192 1 N2 N , N - D i m e t h y l a c e t a m i d e 165 1 N3 C y c l o h e x y l a m i n e 134 2 N4 P y r i d i n e 115 4 N5 I s o b u t y r o n i t r i l e 107 8 N6 T r i e t h y l a m i n e 89 9 S u l p h u r c o n t a i n i n g compounds as 1 % S i n x y l e n e F i g u r e 30. N o n m e t a l e m i s s i o n i n t e n s i t y as a f u n c t i o n o f t h e b o i l i n g p o i n t o f t h e s o l u t e s . Compounds and b o i l i n g p o i n t s see T a b l e IV. 7 6 f i v e f o l d i n c r e a s e i n e m i s s i o n i n t e n s i t y . W h e t h e r t h i s was c a u s e d by an e f f e c t i n t h e n e b u l i z e r chamber, was t h e n t e s t e d i n t h e f o l l o w i n g manner. The waste e f f l u e n t f r o m t h e s p r a y c h a m b e r was r e i n t r o d u c e d i n t o t h e n e b u l i z e r u s i n g t h e pump s y s t e m . The d e l i v e r y r a t e was 3 m l / min and a t o t a l volume o f about 10 ml was c y c l e d t h r o u g h the a s s e m b l y . Four compounds w i t h w i d e l y d i f f e r i n g b o i l i n g p o i n t s ( 2 - o c t a n o l - 177 °C, i s o p r o p a n o l - 82 °C, m e t h a n o l -65 °C and a c e t o n e - 56 °C) were added t o x y l e n e t o y i e l d 1 % oxygen each. The p l o t s o f oxygen e m i s s i o n i n t e n s i t i e s v e r s u s t i m e i n F i g 31 show t h a t t h e l o w e r b o i l i n g c o m p o u n d s g a v e h i g h e r i n t e n s i t i e s a t f i r s t and t h e n d e c a y e d r a p i d l y , whereas t h e l e s s v o l a t i l e ones s t a r t e d l o w e r but r e m a i n e d a t r e l a t i v e l y h i g h l e v e l s f o r l o n g e r . T h e r e f o r e , r e d i s t r i b u t i o n i s t h e c a u s e o f t h i s i n t e r f e r e n c e . The n o n m e t a l p a r e n t compound becomes e n r i c h e d i n t h e a e r o s o l s t r e a m t o t h e t o r c h w h i l e t h e w a s t e e f f l u e n t l o s e s t h a t s u b s t a n c e . The m o s t l i k e l y e x p l a n a t i o n f o r t h i s e f f e c t i s t h a t t h e v o l a t i l e compounds e v a p o r a t e f r o m t h e a e r o s o l d r o p l e t s and r e a c h th e p l a s m a as vapour. The amount w h i c h e v a p o r a t e s , i s o f c o u r s e dependent on t h e b o i l i n g p o i n t o f t h e compound. However, the p o i n t s i n F i g . 30 do n o t f a l l on s m o o t h c u r v e s . T h e r e f o r e , b e s i d e s t h e b o i l i n g p o i n t s o f t h e s o l u t e s , o t h e r c ompound p r o p e r t i e s must e x e r t an i n f l u e n c e . B e c a u s e t h e s t a n d a r d s a r e o f 77 0 10 20 Time (min) F i g u r e 31. Decay o f oxygen e m i s s i o n i n t e n s i t i e s when sample r e c y c l e d f r o m t h e s p r a y c h a m b e r d r a i n o u t l e t b a c k t r o u g h n e b u l i z e r . 1 % oxygen i n x y l e n e . % - m e t h a n o l • - i s o p r o p a n o l A - a c e t o n e • - 2 - o c t a n o l . 78 d i f f e r e n t m o l e c u l a r s t r u c t u r e t h e y c o n t a i n d i f f e r e n t p e r c e n t a g e s o f t h e n o n m e t a l e l e m e n t a n d a c c o r d i n g l y d i f f e r e n t a m o u n t s o f t h e s u b s t a n c e s w e r e a d d e d t o x y l e n e . The v a p o u r p r e s s u r e d e p e n d s n o t o n l y on t h e b o i l i n g p o i n t but a l s o on t h e c o n c e n t r a t i o n and t h e n a t u r e o f t h e v o l a t i l e s p e c i e s . The amount o f sample r e a c h i n g t h e p l a s m a as vapour c o n t a i n s v a r y i n g amounts o f t h e n o n m e t a l a g a i n i n dependence of t h e m o l e c u l a r s t r u c t u r e . 3.5.1.2 NONVOLATILE SOLUTES Compounds w i t h b o i l i n g p o i n t s h i g h e r t h a n 200°C d i d not show a d e t e c t a b l e v o l a t i l i t y e n h a n c e m e n t e f f e c t . T a b l e V g i v e s a l i s t o f n o n v o l a t i l e c o m p o u n d s w h i c h w e r e t e s t e d . A g a i n , t h e s o l u t i o n s c o n t a i n e d 1 % oxygen, 3 % n i t r o g e n or 1 % s u l p h u r i n x y l e n e . P r o b l e m s o c c u r r e d w i t h t h e s o l u t i o n s o f s o m e o f t h e s o l i d s , b e c a u s e t h e y t e n d e d t o c l o g t h e c a p i l l a r y o f t h e c o n c e n t r i c n e b u l i z e r . 79 TABLE V N o n v o l a t i l e S o l u t e s Compound B.P. R e l a t i v e (°C) Response Oxygen c o n t a i n i n g compounds N i t r o b e n z e n e 3 - P h e n y l - l - p r o p a n o l P h e n o l 8 - H y d r o x y q u i n o l i n e N - M e t h y 1 - N - n i t r o s o - p -- t o l u e n e s u l f o n a m i d e as 1 % 0 i n x y l e n e 210 0.96+/-0.07 235 0.97+/-0.07 s o l i d 0.96+/-0.07 s o l i d 1.05+/-0.07 s o l i d 1.04+/-0.07 N i t r o g e n c o n t a i n i n g compounds as 3 % N i n x y l e n e N i t r o b e n z e n e D i p h e n y l a m i n e B i p y r i d i n e A zobenzene N - M e t h y 1 - N - n i t r o s o - p -- t o l u e n e s u l f o n a m i d e 210 s o l i d s o l i d s o l i d s o l i d 1.1+/-0.1 0.9+/-0.1 1.0+/-0.1 0.9+/-0.1 1.0+/-0.1 S u l p h u r c o n t a i n i n g compounds as I I S i n x y l e n e D i p h e n y l d ' i s u l f i d e s o l i d 1.00+/-0.02 D i p h e n y l s u l f o x i d e s o l i d 0.99+/-0.02 N - M e t h y 1 - N - n i t r o s o - p -- t o l u e n e s u l f o n a m i d e s o l i d 1.01+/-0.02 80 Note, t h a t i n F i g . 30 t h e n o n m e t a l e m i s s i o n i n t e n s i t i e s o f t h e s e n o n v o l a t i l e s t a n d a r d s w o u l d a p p e a r a s u n i t y , i . e . f a l l on t h e z e r o l i n e o f t h e l o g s c a l e . The i n t e n s i t i e s o f t h e v o l a t i l e s t h e r e f o r e a r e g i v e n a s m u l t i p l e s o f t h e n o n v o l a t i l e r e s p o n s e . I t was f o u n d , t h a t when n o n v o l a t i l e s a m p l e s w e r e d e t e r m i n e d , t h e t i m e t o r e a c h a s t a b l e s i g n a l a f t e r t h e s w i t c h o v e r o f s a m p l e s i s much s h o r t e r t h a n f o r v o l a t i l e s a m p l e s . T h i s i s c o n s i s t e n t w i t h t h e a b o v e d e s c r i b e d v o l a t i l i t y e f f e c t when one a s s u m e s t h a t v a p o u r and s m a l l d r o p l e t s a r e f l u s h e d f r o m t h e n e b u l i z e r l e s s r a p i d l y t h a n d r o p l e t s . T h i s o b s e r v a t i o n a l s o e x p l a i n s t h e p a r t i c u l a r l y l o n g s w i t c h o v e r t i m e s e x p e r i e n c e d w i t h t h e pump d e l i v e r y s y s t e m , b e c a u s e o n l y v o l a t i l e c o m p o u n d s had b e e n u s e d f o r t h o s e e x p e r i m e n t s . 81 3.5.2 AMOUNTS OF AMBIENT OXYGEN AND NITROGEN The a m o u n t s o f a m b i e n t o x y g e n and n i t r o g e n ( f r o m t h e s o l v e n t and t h e a r g o n s u p p l y ) were t y p i c a l l y e q u i v a l e n t t o 2.7 % oxygen and 8.1 % n i t r o g e n a s p i r a t e d as n o n v o l a t i l e s i n x y l e n e . 3.5.3 SIGNAL TO BACKGROUND RATIOS S i g n a l t o b a c k g r o u n d r a t i o s were d e t e r m i n e d a s : 0.064, 0 . 0 0 5 7 a n d 1.4 f o r o x y g e n , n i t r o g e n a n d s u l p h u r r e s p e c t i v e l y , f o r a n a n a l y t e c o n c e n t r a t i o n o f 1 % n o n v o l a t i l e s . A m b i e n t a m o u n t s o f o x y g e n and n i t r o g e n w e r e c o u n t e d as b a c k g r o u n d . 3.5.4 DRIFTS D r i f t s o f s i g n a l i n t e n s i t i e s w e r e f o u n d t o a f f e c t t h e d e t e c t i o n o f a l l t h r e e e l e m e n t s . I n a l l t h r e e c a s e s t h e u n c e r t a i n t y of t h e measurements i n t r o d u c e d by t h e s e d r i f t s e x c e e d e d random n o i s e f l u c t u a t i o n s o f t h e s i g n a l . A m a j o r c o n t r i b u t i o n was a d r i f t o f t h e c o n t i n u u m b a c k g r o u n d i n t e n s i t i e s . T h i s i s n o t s u r p r i s i n g c o n s i d e r i n g t h e s i g n a l t o b a c k g r o u n d r a t i o s . B a c k g r o u n d i n t e n s i t i e s were f o u n d t o i n c r e a s e by 1.5 % and 2.8 % i n one h o u r a t t h e o x y g e n and s u l p h u r l i n e s r e s p e c t i v e l y . T h i s a m o u n t s t o t h e 82 e q u i v a l e n t o f t h e i n t e n s i t i e s o f 0.2 % and 0.02 % m e a s u r e d oxygen and s u l p h u r r e s p e c t i v e l y o f n o n v o l a t i l e s o l u t e s . The b a c k g r o u n d a t t h e 820 nm n i t r o g e n l i n e was f o u n d t o d e c r e a s e by 0.6 % p e r h o u r w h i c h i s e q u i v a l e n t t o a b o u t 1 % m e a s u r e d n i t r o g e n . The a m b i e n t oxygen i n t e n s i t y ( f r o m i m p u r i t i e s i n x y l e n e and t h e a r g o n s u p p l y ) was f o u n d t o d e c r e a s e o v e r t i m e t o a n a m o u n t s l i g h t l y e x c e e d i n g t h e i n c r e a s e o f t h e b a c k g r o u n d , w h e r e a s no d r i f t o f a m b i e n t n i t r o g e n was d e t e c t e d . I n t e n s i t i e s due t o o x y g e n and s u l p h u r c o n t a i n e d i n s a m p l e s a p p e a r e d t o be r a t h e r s t a b l e . C o r r e s p o n d i n g d a t a f o r n i t r o g e n i s not a v a i l a b l e b e c a u s e l i m i t e d work was done w i t h t h i s e l e m e n t . The u s e o f a p h o t o d i o d e a r r a y a l l o w e d us t o m o n i t o r and c o r r e c t f o r t h e s e d r i f t s as f a r as b a c k g r o u n d was c o n c e r n e d , by m e a s u r i n g t h e i n t e n s i t y o f t h e b a c k g r o u n d c l o s e t o t h e a n a l y t i c a l l i n e . A s u s p e c t e d r e a s o n f o r t h e s e d r i f t s was i n s u f f i c i e n t t h e r m a l s t a b i l i t y o f t h e n e b u l i z e r t o r c h a s s e m b l y . The t e m p e r a t u r e i n t h e p l a s m a box was f o u n d t o r i s e t o a b o u t 5 0 ° C when t h e ICP was i n u s e . H e a t i n g o f t h e n e b u l i z e r a s s e m b l y must c h a n g e t r a n s p o r t e f f i c i e n c i e s and t h e i m p l e m e n t e d c o o l i n g o f t h e s p r a y c h a m b e r was n o t s u f f i c i e n t t o overcome t h i s p r o b l e m . B a c k g r o u n d i n t e n s i t i e s d e c r e a s e d i n a l l t h r e e s p e c t r a l r e g i o n s w i t h s a m p l e l o a d compared t o t h e pure a r g o n p l a s m a . T h e r e f o r e , an i n c r e a s e i n 83 t h e b a c k g r o u n d p o i n t s t o a d e c r e a s i n g n e b u l i z e r e f f i c i e n c y . However, t h i s i s not c o n s i s t e n t w i t h a d e c r e a s i n g b a c k g r o u n d i n t e n s i t y f o u n d a t 820 nm. D r i f t s a r e not u n u s u a l i n ICP e m i s s i o n s p e c t r o s c o p y and p o s e a p r o b l e m a l s o when a q u e o u s s a m p l e s a r e a n a l y z e d . L o r b e r e t a l . h a v e r e p o r t e d a d r i f t o f m e t a l e m i s s i o n i n t e n s i t i e s o f up t o 5 % w i t h i n 30 m i n u t e s [ 6 3 ] . 3 . 5 . 5 DETECTION L IM ITS OXYGEN: The e m i s s i o n i n t e n s i t y f o r 1 % oxygen as n i t r o b e n z e n e , a n o n v o l a t i l e s t a n d a r d , was measured. The i n t e g r a t i o n t i m e o f t h e p h o t o d i o d e a r r a y was s e t t o 2.5 s w h i c h y i e l d e d a p p r o x i m a t e l y 75 % s a t u r a t i o n o f t h e a r r a y a t t h e a n a l y t e l i n e . T he n o i s e o f t h e a m b i e n t o x y g e n c o n c e n t r a t i o n was d e t e r m i n e d a s t h e s t a n d a r d d e v i a t i o n o f 20 c o n s e c u t i v e r e a d i n g s o f t h e a r r a y . The d r i f t s d i d n o t i n f l u e n c e t h e s e r e a d i n g s b e c a u s e o f t h e s h o r t t i m e d u r a t i o n o f t h e e x p e r i m e n t . The c o n c e n t r a t i o n e q u i v a l e n t t o t h r e e t i m e s t h e n o i s e o f t h e a m b i e n t c o n c e n t r a t i o n , t h e d e t e c t i o n l i m i t , was d e t e r m i n e d a s : 1.0 g/1 o x y g e n i n x y l e n e . 84 NITROGEN: T h e d e t e c t i o n l i m i t f o r n i t r o g e n was d e t e r m i n e d s i m i l a r l y u s i n g t h e 821 nm l i n e , w i t h 3 % n i t r o g e n a s n i t r o b e n z e n e i n x y l e n e and an i n t e g r a t i o n t i m e o f 3.0 s. I t was f o u n d t o be 16 g / l n i t r o g e n i n x y l e n e . T he d e t e c t i o n l i m i t f o r n i t r o g e n i n w a t e r c o u l d n o t be d e t e r m i n e d , b e c a u s e i t i s h i g h e r t h a n 50 g / l . SULPHUR: The d e t e c t i o n l i m i t f o r s u l p h u r was d e t e r m i n e d as t h e e m i s s i o n i n t e n s i t y e q u i v a l e n t t o t h r e e t i m e s t h e n o i s e o f t h e b a c k g r o u n d . S o l u t i o n s o f 0 . 1 2 5 % s u l p h u r a s d i p h e n y 1 d i s u 1 f i d e i n x y l e n e a n d 0.5 % s u l p h u r a s s u l f o s a l i c y l i c a c i d i n w a t e r were used t o measure t h e l i n e i n t e n s i t i e s . The d e t e c t i o n l i m i t s w e r e d e t e r m i n e d a s : 120 mg/1 s u l p h u r i n x y l e n e and 390 mg/1 s u l p h u r i n w a t e r . The d e t e c t i o n l i m i t i n w a t e r i s p o o r e r b e c a u s e t h e t r a n s p o r t e f f i c i e n c y f o r x y l e n e i s b e t t e r , and t h e o p t i m i z a t i o n was done f o r x y l e n e a s p i r a t i o n . T a b l e VI s u m m a r i z e s t h e d e t e c t i o n l i m i t s and g i v e s t h e r e p o r t e d VUV v a l u e s f o r x y l e n e f o r c o m p a r i s o n . 85 TABLE VI D e t e c t i o n L i m i t s Nonmetal S o l v e n t NIR (PDA) VUV (PMT) Oxygen X y l e n e 1.0 g/1 N i t r o g e n X y l e n e 16 g/1 100 mg/l [32] Water >50 g/1 S u l p h u r X y l e n e 120 mg/l 0.05 mg/l [33] Water 390 mg/l When c o m p a r i n g t h e NIR- and VUV d e t e c t i o n l i m i t s , i t h a s t o be c o n s i d e r e d , t h a t t h e PMTs a r e i n h e r e n t l y p h o t o n a m p l i f i e r s , w h i l e t h e PDA i s n o t . D e p e n d i n g on t h e n a t u r e of th e n o i s e d e t e r m i n i n g t h e d e t e c t i o n l i m i t , t h e use of a PMT o r an i n t e n s i f i e d PDA f o r t h e d e t e c t i o n o f t h e NIR l i n e s m i g h t i m p r o v e t h o s e d e t e c t i o n l i m i t s by p e r h a p s t h r e e o r d e r s o f m a g n i t u d e . H o w e v e r , a l l P M T s h a v e a s h a r p d r o p o f s e n s i t i v i t y a t 900 nm, so t h a t t h e i r s e n s i t i v i t y f o r t h e 920 nm s u l p h u r l i n e c a n be e x p e c t e d t o be r e l a t i v e l y p o o r . D e t e c t i o n l i m i t s f o r PMTs c o u l d n o t be d e t e r m i n e d , b e c a u s e of a l a c k o f n e c e s s a r y e q u i p m e n t . The m e a s u r e d d e t e c t i o n l i m i t s p r o v i d e o n l y a r o u g h g u i d e l i n e . An i n c r e a s e o f i n t e g r a t i o n t i m e o r s i g n a l a v e r a g i n g d e c r e a s e s r a n d o m n o i s e and i m p r o v e s d e t e c t i o n l i m i t s . T h e n , an o p t i m i z a t i o n o f w o r k i n g c o n d i t i o n s ( f l o w r a t e s , l o a d p o w e r and v i e w i n g h e i g h t ) f o r s i g n a l t o n o i s e 86 r a t i o m o s t l i k e l y w o u l d i m p r o v e t h e f i g u r e s a s w e l l . A p r o p e r o p t i m i z a t i o n o f t h e w o r k i n g c o n d i t i o n s i s not t r i v i a l b e c a u s e i t i s n o t c l e a r how t h e d i f f e r e n t p a r a m e t e r s i n t e r a c t . S i m p l y c h a n g i n g one p a r a m e t e r a t a t i m e d o e s n o t n e c e s s a r i l y l e a d t o a n o p t i m u m . F o r t h i s r e a s o n , a m a t h e m a t i c a l a i d , t h e " S i m p l e x M e t h o d " i s t h e r e f o r e s o m e t i m e s used t o o p t i m i z e ICP w o r k i n g c o n d i t i o n s [ 6 4 ] , Not s u r p r i s i n g l y , t h e d e t e c t i o n l i m i t s f o l l o w t h e o r d e r o f t h e u p p e r s t a t e e n e r g y l e v e l s o f t h e r e s p e c t i v e l i n e s , w h i c h a r e : 7.9 eV f o r s u l p h u r , 10.7 eV f o r o x y g e n and 11.8 eV f o r n i t r o g e n [21,22,28], An e s t i m a t e o f x y l e n e d e t e c t i o n l i m i t s f o r o t h e r n o n m e t a l l i n e s i n t h e n e a r i n f r a r e d c o u l d be made on t h i s b a s i s . 3.5.6 WORKING CURVES OXYGEN: Wo r k i n g c u r v e s f o r two " n o n v o l a t i l e " ( n i t r o b e n z e n e and 3 - p h e n y l - l - p r o p a n o l ) and two " v o l a t i l e " ( d i m e t h y l s u l f o x i d e and a c e t i c a c i d a n h y d r i d e ) oxygen c o n t a i n i n g compounds a r e shown i n F i g . 32. The n o n v o l a t i l e s u b s t a n c e s gave i d e n t i c a l a nd l i n e a r c u r v e s , w h i l e t h e v o l a t i l e c o m p o u n d s s t i l l p r o d u c e d l i n e a r c u r v e s but a t h i g h e r o v e r a l l i n t e n s i t i e s . 87 NITROGEN: W o r k i n g c u r v e s f o r n i t r o g e n were not a c q u i r e d b e c a u s e of t h e r e l a t i v e l y low s e n s i t i v i t y . SULPHUR: W o r k i n g c u r v e s f o r b o t h d i p h e n y 1 d i s u 1 f i d e a n d d i m e t h y l s u l f o x i d e were f o u n d t o be l i n e a r and a r e p r e s e n t e d i n F i g u r e 33. 88 Oxygen in Xylene (%) F i g u r e 32. Working c u r v e s o f oxygen i n x y l e n e . #- N i t r o b e n z e n e , *'- 3 - P h e n y l - l - p r o p a n o l A - D i m e t h y l s u l f o x i d e , m~— A c e t i c a c i d a n h y d r i d e 89 0.0625 0.125 0.25 0.5 I 2 4 Sulphur in Xylene (%) F i g u r e 3 3 . Working c u r v e s f o r s u l p h u r i n x y l e n e . +- D i p h e n y l d i s u l f i d e , Q- D i m e t h y l s u l f o x i d e 90 3.5.7 CERTIFIED OIL STANDARDS FOR SULPHUR As a f i n a l c h e c k o f t h e u s e f u l n e s s o f t h e m e t h o d f o r the d e t e r m i n a t i o n of s u l p h u r i n o i l s a m p l e s , f i v e c e r t i f i e d s t a n d a r d s f r o m t h e US N a t i o n a l B u r e a u o f S t a n d a r d s (NBS) were t e s t e d . The s t a n d a r d s were d i l u t e d i n x y l e n e t o m i n i m i z e m a t r i x e f f e c t s due t o d i f f e r e n t p h y s i c a l p r o p e r t i e s . However, t h e e x t e n t of t h i s d i l u t i o n was l i m i t e d by t h e d e t e c t i o n l i m i t . A w o r k i n g c u r v e f r o m 0 . 0 6 2 5 t o 2 % s u l p h u r a s d i p h e n y I d i s u l f i d e i n x y l e n e was e m p l o y e d . The r e s u l t s a r e l i s t e d i n T a b l e V I I . TABLE V I I NBS Samples S t a n d a r d D i l u t i o n % S f o u n d %S c e r t i f i e d A c c u r a c y (g/50ml) 1620a 5 4.1+/-0.1 4.504+/-0.010 91 % 1621b 10 0.80+/-0.02 0.950+/-0.005 84 % 1622b 5 1.9+/-0.1 1.982+/-0.018 96 % 1623a 20 0.15+/-0.02 0.240+/-0.001 63 % 1624a n e a t 0.065+/-0.02 0.141+/-0.002 46 % 91 As a c o m p a r i s o n o f t h e d e t e r m i n e d and t h e c e r t i f i e d c o n c e n t r a t i o n s s h o w s , t h e r e s u l t s w e r e more a c c u r a t e t h e more t h e s t a n d a r d s w e r e d i l u t e d ( s e e l a s t c o l u m n i n T a b l e V I I , a c c u r a c y = d e t e r m i n e d c o n c e n t r a t i o n i n % o f c e r t i f i e d c o n c e n t r a t i o n ) . T h i s s t r o n g l y p o i n t s t o r e d u c e d t r a n s p o r t e f f i c i e n c i e s , i . e . r e d u c e d a m o u n t s o f t h e s a m p l e s r e a c h i n g t h e p l a s m a b e c a u s e o f r e d u c e d d e l i v e r y r a t e s and / o r n e b u l i z e r e f f i c i e n c y . Whether t h i s was t r u e was i n v e s t i g a t e d i n two ways. T h r e e o f t h e s a m p l e s w e r e d i l u t e d by a h i g h e r f a c t o r t o c h e c k w h e t h e r a d e c r e a s e i n v i s c o s i t y w o u l d i n c r e a s e t h e a c c u r a c y . The r e s u l t s a r e g i v e n below i n T a b l e V I I I . TABLE V I I I D i l u t i o n s S t a n d a r d D i l u t i o n % S f o u n d % S c e r t i f i e d A c c u r a c y 1620a 5 g/50ml 4.1 4.504 91 % 2 g/50ml 4.5 100 % 1621b 10 g/50ml 0.80 0.950 84 % 5 g/50ml 0.88 93 % 1622b 5 g/50ml 1.9 1.982 96 % 2.5 g/50ml 2.1 106 % The a c c u r a c y i m p r o v e d i n two c a s e s and i n one c a s e i t i n c r e a s e d t o above 100 %. 92 A s e c o n d c h e c k was done by m a k i n g a s t a n d a r d a d d i t i o n of s u l p h u r as d i p h e n y l d i s u l f i d e . I f a l l o f t h e added s u l p h u r i s r e c o v e r e d , t h e n t h e t r a n s p o r t e f f i c i e n c y i s t h e same as f o r t h e s o l u t i o n s u s e d f o r t h e a c q u i s i t i o n o f t h e w o r k i n g c u r v e and a n o t h e r m a t r i x e f f e c t must t a k e p l a c e . The r e s u l t s a r e g i v e n i n T a b l e IX. TABLE IX S t a n d a r d A d d i t i o n s S t a n d a r d D i l u t i o n 1620a 1621b 1623a 5 g/50ml 2 g/50ml 10 g/50ml 20 g/50ml A d d i t i o n 0.50 % 0.20 % 0.10 % 0.10 % R e c o v e r y o f added S u l p h u r 94 % 95 % 86 % 69 % C o r r e c t e d a c c u r a c y ( s e e t e x t ) 97 % 105 % 98 % 91 % C o m p a r i n g th e a c c u r a c y o f t h e s u l p h u r d e t e r m i n a t i o n i n t h e c e r t i f i e d s a m p l e s ( T a b l e V I I ) w i t h t h e r e c o v e r y o f t h e a d d e d s u l p h u r ( T a b l e IX) s h o w s t h a t t h e s e m a t c h q u i t e c l o s e l y . When t h e r e c o v e r y o f t h e a d d e d s u l p h u r i s t a k e n i n t o a c c o u n t when c a l c u l a t i n g t h e s u l p h u r c o n c e n t r a t i o n s i n t h e s t a n d a r d s , t h e e r r o r s become much s m a l l e r ( s e e T a b l e IX, c o r r e c t e d a c c u r a c y ) . 93 An o t h e r i n d i c a t i o n f o r a t r a n s p o r t e f f i c i e n c y i n t e r f e r e n c e i s t h e f a c t t h a t t h e b a c k g r o u n d i n t e n s i t i e s were h i g h e r when th e d i l u t e d NBS s a m p l e s were measured t h a n when p u r e x y l e n e was a s p i r a t e d . T a b l e X g i v e s a l i s t o f t h e s e s h i f t s . TABLE X B a c k g r o u n d S h i f t s a t 920 nm when NBS s t a n d a r d s i n x y l e n e a r e a s p i r a t e d S t a n d a r d 1620a 1621b 1622b 1623a D i l u t i o n B a c k g r o u n d I n c r e a s e (% BG) (a s % S) 5 g/50ml 4.6 0.033 5 g/50ml+0.5 % S 4.5 0.032 2 g/50ml 2.4 0.017 2 g/50ml 1 . 0 0.007 10 g/50ml 3.1 0.022 10 g/50ml+0.1 % S 2.8 0.020 5 g/50ml 1.4 0.010 5 g/50ml 2.8 0.020 2.5 g/50ml 1.7 0.012 20 g/50ml 3.8 0.027 20 g/50ml+0.1 % S 4.6 0.033 G e n e r a l l y b a c k g r o u n d i n t e n s i t i e s were f o u n d t o d e c r e a s e w i t h a s p i r a t i o n r a t e when o r g a n i c s o l v e n t s were i n t r o d u c e d . 94 T h e r e f o r e , t h e h i g h e r t h e b a c k g r o u n d i n t e n s i t y , t h e s m a l l e r t h e s a mple l o a d i n t h e p l a s m a and t h e s m a l l e r t h e t r a n s p o r t e f f i c i e n c y . H i g h e r b a c k g r o u n d i n t e n s i t i e s were i n d e e d f o u n d f o r t h e l e s s d i l u t e d N B S - s a m p l e s . T h e s e s h i f t s d i d n o t a f f e c t t h e m e a s u r e d q u a n t i t i e s b e c a u s e t h e b a c k g r o u n d was s u b t r a c t e d . T h i s e f f e c t s h o w s a g a i n t h e i m p o r t a n c e o f m o n i t o r i n g t h e b a c k g r o u n d i n t e n s i t y t o o b t a i n a c c u r a t e r e s u l t s . G e n e r a l l y , t h e r e s u l t s o b t a i n e d compare w e l l w i t h t h e ones o f W a l l a c e [32] f o r s i m i l a r NBS s t a n d a r d s when d i l u t e d 1:100 w i t h x y l e n e u s i n g a VUV l i n e a t 180 nm. The a c c u r a c i e s f o r f o u r s t a n d a r d s w e r e 97, 102, 85 and 102 % ( W a l l a c e d i d n o t c o m p a r e t h e NBS s a m p l e s w i t h a w o r k i n g c u r v e , b u t t o o k t h e a c c u r a c y o f t h e s t a n d a r d w i t h t h e h i g h e s t s u l p h u r c o n c e n t r a t i o n as 100 % and measured t h e t h e r e s p o n s e of t h e o t h e r s t a n d a r d s on t h a t p a r t i c u l a r s a m p l e ) . T h e f a c t t h a t t h e e x p e r i m e n t a l l y d e t e r m i n e d c o n c e n t r a t i o n s o f s u l p h u r i n t h e NBS-samples d i d not e x c e e d t h e c e r t i f i e d v a l u e s ( e x c e p t i n one c a s e ) means t h a t no v o l a t i l i t y r e d i s t r i b u t i o n o c c u r e d . T h e r e f o r e , t h e s u l p h u r c o n t a i n i n g c o m p o u n d s i n t h e o i l s a m p l e s must be o f l o w v o l a t i l i t y . 95 CHAPTER IV CONCLUSION O x y g e n i n an o r g a n i c l i q u i d was d e t e r m i n e d f o r t h e f i r s t t i m e w i t h ICP-OES. N e a r - i n f r a r e d e m i s s i o n l i n e s were u s e d f o r t h e d e t e r m i n a t i o n o f t h a t e l e m e n t as w e l l as n i t r o g e n and s u l p h u r . The d e t e c t i o n l i m i t s were d e t e r m i n e d as 1.0 g / l , 16 g / l a n d 120 mg/1 i n x y l e n e f o r o x y g e n , n i t r o g e n a n d s u l p h u r r e s p e c t i v e l y . T h e s e n o n r e s o n a n t e m i s s i o n l i n e s p r o v e d t h e r e f o r e t o be much l e s s s e n s i t i v e t h a n t h e r e s p e c t i v e v a c u u m - u l t r a v i o l e t l i n e s . However, t h e d e t e c t i o n o f t h e n e a r - i n f r a r e d l i n e s d o e s n o t r e q u i r e a p u r g i n g or e v a c u a t i o n o f t h e l i g h t p a t h . W o r k i n g c u r v e s f o r oxygen and s u l p h u r were f o u n d t o be l i n e a r . A w o r k i n g c u r v e f o r n i t r o g e n was n o t a c q u i r e d b e c a u s e o f t h e r e l a t i v e l y low s e n s i t i v i t y f o r t h a t e l e m e n t . S u l p h u r i n c e r t i f i e d o i l s t a n d a r d s ( N a t i o n a l B u r e a u o f S t a n d a r d ) was d e t e r m i n e d s u c c e s s f u l l y , e v e n t h o u g h t h e r e l a t i v e l y low s e n s i t i v i t y c a u s e d some l i m i t a t i o n s . Not a l l o f t h e s a m p l e s c o u l d be d i l u t e d s u f f i c i e n t l y t o e l i m i n a t e i n t e r f e r e n c e e f f e c t s . T h e r e f o r e t h e s t a n d a r d a d d i t i o n method had t o be u s e d . A d i l u t i o n f a c t o r o f a b o u t 10 i s deemed t o be n e c e s s a r y t o e l i m i n a t e i n t e r f e r e n c e e f f e c t s w i t h t h e NBS o i l s a m p l e s . 96 T h e e n t r a i n m e n t o f a i r i n t o t h e p l a s m a d i d n o t i n t e r f e r e w i t h t h e d e t e r m i n a t i o n o f o x y g e n and n i t r o g e n , b e c a u s e t h e h i g h e s t e m i s s i o n i n t e n s i t i e s f o r t h e s e e l e m e n t s w e r e f o u n d l o w i n t h e p l a s m a , w h e r e t h a t e f f e c t i s n o t s i g n i f i c a n t . A t o m i z a t i o n o f t h e o r g a n i c s a m p l e s i n t h e p l a s m a r e g i o n s where a t o m i c n o n m e t a l e m i s s i o n o r i g i n a t e s was shown t o be c o m p l e t e , so t h a t an i n t e r f e r e n c e e f f e c t due t o i n c o m p l e t e a t o m i z a t i o n i s u n l i k e l y . A c o m p a r i s o n o f a s e r i e s o f s t a n d a r d s , d i s c l o s e d a r e d i s t r i b u t i o n e f f e c t i n t h e s p r a y c h a m b e r when c o m p o u n d s w i t h b o i l i n g p o i n t s below 200 °C were used. T h i s l i m i t s t h e u s e o f t h e m e t h o d t o n o n v o l a t i l e s p e c i e s o r w e l l d e f i n e d s y s t e m s s u c h as e l e m e n t s e l e c t i v e d e t e c t i o n i n l i q u i d c h r o m a t o g r a p h y . The e l i m i n a t i o n o f t h e s p r a y c h a m b e r by n e b u l i z i n g t h e s a m p l e s d i r e c t l y i n t o t h e p l a s m a c o u l d o v e r c o m e t h i s l i m i t a t i o n . S u c h a s y s t e m was r e p o r t e d r e c e n t l y by L a w r e n c e e t a l . [ 6 5 ] , D i r e c t f o r c e d s a m p l e i n t r o d u c t i o n i n t o the p l a s m a would a l s o e l i m i n a t e t h e need f o r m a t r i x m a t c h i n g i m p o s e d by t h e v a r i o u s i n t e r f e r e n c e e f f e c t s a t t h e a e r o s o l p r o d u c t i o n s t e p and v e r y l i k e l y would i m p r o v e t h e d e t e c t i o n l i m i t s somewhat b e c a u s e t h e a s p i r a t i o n r a t e f o r x y l e n e c a n be h i g h e r t h a n t h e n a t u r a l o n e . D e t e c t i o n l i m i t s p r o b a b l y c o u l d a l s o be i m p r o v e d by a s s u r i n g b e t t e r d i f f u s i o n of t h e sample i n t o t h e low t o r o i d a l r e g i o n 97 o f t h e p l a s m a by a l o w n e b u l i z e r g a s f l o w r a t e i n c o m b i n a t i o n w i t h f o r c e d s a m ple f e e d . 98 BIBLIOGRAPHY 1. S. G r e e n f i e l d , I . L I . J o n e s and C.T. B e r r y , A n a l y s t , 89, 713 ( 1 9 6 4 ) . 2. R. H. Wendt and V. A. 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