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The spectrophotometric identification of the permitted synthetic food colours Davies, Francis Raymond Edward 1949

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L-1= "5  THE  SPECTROPHOTOMETRY OF  THE  IDENTIFICATION  PERMITTED SYNTHETIC  FOOD  COLOURS.  Francis Raymond Edward Davies  A Thesis Submitted i n P a r t i a l Fulfilment of the Requirements f o r the Degree of MASTER  OF  ARTS  i n the Department of CHEMISTRY  THE  UNIVERSITY  OF  BRITISH  SEPTEMBER, 1949  COLUMBIA  \  Page \.  ABSTRACT  Thirteen mitted the  s p e c i f i e d water soluble dyes a r e per-  f o r use i n e d i b l e products  United  States.  The o f f i c i a l  a n a l y s i s i s not very are present analysis  with  c h e m i c a l - p h y s i c a l method of  s u c c e s s f u l when s m a l l amounts  l a r g e r amounts  of a s i n g l e  consumed i n C a n a d a and  of o t h e r s ,  dye i f p r e s e n t  o f one dye  o r e v e n i n the  i n small quantities.  The  s p e c t r o p h o t o m e t e r h a s been shown t o be v e r y u s e f u l i n i d e n t i fying  the t h i r t e e n  permitted  d y e s i n d i v i d u a l l y , and by i t s  means many p r e v i o u s l y u n r e s o l v a b l e r e a d i l y analyzed. o f t h i s method  Further  binary mixtures  have been  i n v e s t i g a t i o n o f the p o s s i b i l i t i e s  of a n a l y s i s i s  proceeding.  Page 1 .  ACKNOWLEDGEMENT Although  this  T h e s i s i s based upon independent  research, carried of  out e n t i r e l y  i n the Laboratories  t h e Department o f N a t i o n a l H e a l t h and W e l f a r e ,  V a n c o u v e r , B.C., I am p r o f o u n d l y Dr.  J . ALLEN HARRIS,  Professor o f Chemistry British in  indebted t o  at the University of  Columbia, f o r h i s a d v i c e and encouragement  the completion  o f t h i s work.  i n acknowledging h i s  sponsorship.  I have  pleasure  Page The S p e c t r o p h o t o m e t r y of  Identification  the P e r m i t t e d S y n t h e t i © Food  Colours.  CONTENTS Section  Page Number  Abstraot  5  Introduction  4  Methods o f P r o c e d u r e  6  Analysis  8  of Data  References  15  Errata  15  Plate  1  Plate  2 .... The G r e e n Dyes  16  Plate  J .... The Y e l l o w and Orange Dyes  17  Plate  4 .... The R e d D y e s  17  Plates  The B l u e Dyes  5 and 6..  The L i g h t  16  G r e e n a n d 10% B i n a r i e s  Plate  7 .... G u i n e a  G r e e n and F a s t  Plate  8 .... S u n s e t Y e l l o w and 10% B i n a r i e s  Plate  9 .... T a r t r a z i n e  Plate  10  ... T a r t r a z i n e ,  Green  and 10% B i n a r i e s Brilliant  18 19 1.9 20  B;iue, a n d Indigotine  20  Plate  11 ... A m a r a n t h and 10% B i n a r i e s  21  Plate  12  21  List  ... Grape C o l o u r M i x t u r e s  o f P e r m i t t e d Dyes  22  Page 4. INTRODUCTION The  Food a n d D r u g s A c t o f t h e D o m i n i o n o f Canada a n d t h e  food laws of the United only are  thirteen listed For  specified water-soluble  or  the purpose  of administering  confectionery,  t o be a b l e  these  food.  they  of the food,  and w i t h  reason-  thus i n c r e a s i n g i t s s a l e s  class  i n mere " b l u s h e s "  o n l y as v e r y  part of the e n t i r e c o n f e c t i o n e r i e s , the or p a l e  t i n t s , and  t h i n s u r f a c e washes.  a l l uncommon f o r a c o l o u r t o be p l a i n l y v i s i b l e y e t t o be p r e s e n t  i n such m i c r o s c o p i c  d e t e c t i o n , i n the f o o d  that  beverage,  been e s t a b l i s h e d ,  accuracy  c o n s t i t u t e a v e r y minute  I n d e e d , i n the c a s e o f h i g h  o f t e n a r e there  great  tinctorial  a solution  by o r d i n a r y methods.  of Fast  confectionery  million  t o the e y e  t r a c e s a s to d e f y A s a n example o f  G r e e n , one h u n d r e d p a r t s i n t e n m i l l i o n t h a n many o f t h e t i n t s u s e d i n  t r a d e , a n d two p a r t s o f F a s t  o f water oould  m l . pyrex beaker  I t i s not  powers o f some o f t h e d y e s , i t was f o u n d  of w a t e r , was -much more i n t e n s e  100  i t i s therefore  d y e s a r e added s o l e l y f o r t h e p u r p o s e o f  dyes a r e o f t e n p r e s e n t  the  the Act,  presence having  t h e dyes w i t h  the a p p e a r a n c e  attraction,  the  dyes  s p e e d and s i m p l i c i t y .  improving  and  These  have been added t o a f o o d ,  and, t h e i r  to i d e n t i f y  Since  at  dyes.  t o demonstrate the p r e s e n c e of a r t i f i c i a l  c o l o u r s w h e r e v e r they  able  aniline  the use of  on t h e addendum page f o l l o w i n g P l a t e 1 2 .  n e o e s s a r y t o be a b l e food  S t a t e s o f America permit  Green i n t e n  e a s i l y be d e t e c t e d when c o n t a i n e d  and v i e w e d  by t r a n s m i t t e d  light.  i na  Page Since  a n y dye p r e s e n t i n a f o o d  be a v a i l a b l e ly  impossible  the  will  i n theory could  be p r e s e n t .  There-  T h u s one a t t e m p t s to p r o v e  dyes  any d y e w h i c h  does  t h e presence or absence  o f t h e p e r m i t t e d d y e s , b u t makes no a t t e m p t dyes, merely c l a s s i f y i n g  by e s t a b -  each o f these  f r o m t h e o t h e r p e r m i t t e d d y e s , and r e j e c t i n g  other  identifying  the p e r m i t t e d d y e s  c e r t a i n procedures f o r i s o l a t i n g  conform.  never  o f f o o d d y e s h a s assumed t h e n e g a t i v e  d i r e c t i o n of attempting to detect  not  almost  t o nave p o s i t i v e means o f c h e m i c a l l y  the i d e n t i f i c a t i o n  lishing  sample  i n ordinary "weighable" quantities., i t i s m a n i f e s t -  thousands o f dyes which  fore  3,  to i d e n t i f y  any  them i n a g r o u p a s " n o n - p e r m i t t e d  dyes". There isolate  i s , o f c o u r s e , a n e s t a b l i s h e d method  the p e r m i t t e d dyes, a s d e t a i l e d  "Methods o f A n a l y s i s  i n Chapter ZXI of the  of t h e A s s o c i a t i o n of O f f i c i a l  t u r a l Chemists", S i x t h E d i t i o n ,  194-5. ( 1 ) . h i s T  p r i m a r i l y on the p a r t i t i o n o f t h e dye between immiscible  solvents.  as t o d i v i d e of w h i c h  Conditions are varied  the p e r m i t t e d d y e s  i n turn i s divided  component d y e s . reasonable  into  Agricul-  scheme d e p e n d s  two r e l a t i v e l y  by f o u r  s t a g e s , so  four primary groups,  a r e q u i t e p u r e and p r e s e n t i n  q u a n t i t i e s and i n n o t t o o u n e q u a l amounts,  ideal conditions Y e l l o w F C F does  seldom  satisfactory.  exist  not remain  each  by f u r t h e r m a n i p u l a t i o n i n t o i t s  I f the dyes  scheme o f a n a l y s i s i s f a r i l y  the l a s t  of procedure to  i n practice.  this  Unfortunately Moreover,  Sunset  e n t i r e l y i n the aqueous p h a s e  group, b u t , i f p r e s e n t i n ponderable q u a n t i t y ,  these  until will  Page  6.  a p p e a r i n a l l g r o u p s and  will  w i t h the  i t i s found  little  washings.  Also  t e n d e n c y to p a s s i n t o  cent, h y d r o c h l o r i c However, the i n e q u a l i t y of The  the  by  to a " l i m e "  ordinary  of  attempt  as  was  pair  but  since  to  the  was  made t o u s e  the The  convenient  u l t r a v i o l e t and  vice  that  a l l four  About purpose of States  the  only  to  versa  instrument  t h i s research  by W.O.  trace.  colour,  when  Tartrazine.  the  cells.  By  any  Holmes, J.T.  this  available,  visible  range  same s o l u t i o n s t e s t i t waS  use  dis-  enough t o u s e  in  correction.  of d i r e c t value to  i s the  for  'Quartz S p e c t r o -  c e l l s were  with  applying  available  a means  infrared, accessories.  o e l l s were matched w e l l  reference  of  a mere  g r e e n , the  s w i t c h f r o m the  publication of  Department o f A g r i c u l t u r e ,  J u n e , 1932,  colour  S p e c t r o p h o t o m e t e r as  Silica  silica  i n v e s t i g a t i o n without  great  i n many m i x t u r e s .  change t h e  Photoelectric  b o t h C o r e x and  made e n t i r e l y o f t h e  covered this  i t was  per  PROCEDURE.  a Beckman M o d e l DU  each of  five  f a r i s the  present  p h o t o m e t e r , c o m p l e t e w i t h u l t r a v i o l e t and Two  f r o m the  methods, c o n s i s t e n t l y y i e l d s o n l y  was  III.  for.  f a c t o r by  a shade of  to  t a r t r a z i n e shows very-  scheme c a l l s  to  Groups I  g r e e n shade i s r e l a t i v e l y  i d e n t i f y i n g each food dye.  research  of  amyl a l c o h o l  required  METHODS OF An  that  amounts of e a c h dye  Although c l e a r l y v i s i b l e tested  the  c l e a r out  troublesome  amount o f I n d i g o t i n e  Tartrazine  the  a c i d , as most  not  Technical  the  the  specific  United  B u l l e t i n No.  S c a n l a n , and  A.R.  310,  Peterson,  Page entitled, It avoid and  7.  "The V i s u a l S p e c t r o p h o t o m e t r y o f D y e s . " (2).  should  be n o t e d t h a t  t h e a u t h o r s recommend t h a t one  t h e use o f w a t e r as a s o l v e n t  instead  research  suggest f i f t y  percent,  due t o t a u t o m e r i c a l t e r a t i o n , alcohol.  t h e a q u e o u s s o l u t i o n was a d h e r e d  t h i s i s t h e f o r m i n which  the p r a c t i c a l  encountered.  be t h a t  alcoholic  I t may w e l l  or o t h e r  the p r e l i m i n a r y (1) a s e a r c h  o f previous  in  of the density  o f the d e n s i t y  a few o f t h e s e b i n a r y the r a t i o  component.  An  That part  that  to  curve f o r each permitted t o 700  dye  millimicrons.  curves f o r c e r t a i n  binary  s o l u t i o n s t h e c o m p o n e n t s were  present  m i n o r component i n 90 p e r c e n t ,  major  o f t h e f u l l r a n g e (220 m i l l i m i c r o n s t o  o f the minor  c u r v e o f the m a j o r  show t o  constituent  constituent.  was made t o make u s e o f d y e c o n c e n t r a t i o n s  t h e maximum a b s o r p t i o n  unity  work, i t was d e c i d e d  was r u n f o r e a c h s o l u t i o n w h i c h w o u l d  t h e standard attempt  q u a n t i t a t i v e work, a n  In a l l  what d e g r e e , i f a n y , t h e p r e s e n c e modified  are p r i m a r i l y  ranges o f wavelength.  o f 10 p e r c e n t ,  700 m i l l i m i c r o n s )  because  i n v e s t i g a t i o n s t o the f o l l o w i n g :  mixtures through c e r t a i n s p e c i f i c but  solutions  i n future  t h r o u g h t h e r a n g e 220 m i l l i m i c r o n s (2) a s e a r c h  to p r i m a r i l y  s o l u t i o n w i l l have t o be e m p l o y e d .  In view of t h e p a u c i t y limit  However, i n t h i s  b u t l e s s t h a n 2;  lie  between one p e r c e n t ,  and  Fast  that  would y i e l d  a density  greater  i s , t h e minimum t r a n s m i s s i o n  and 10 p e r c e n t .  Green, the c o n c e n t r a t i o n  such than would  For Guinea Green B  u s e d was one p a r t  i n 100,000.  Page For the other  e l e v e n d y e s the  8.  c o n c e n t r a t i o n was  one  2:5,000, a l t h o u g h f o r f u t u r e work i t i s s u g g e s t e d centrations point  intermediate to  obtained tions  o f I n d i g o t i n e and  c a n be u s e d  invariable  well-known f a c t of  several  that  of t h e s e  Blue  a t a f u t u r e time and  composite  s o l v e n t u s e d was a t pH  pH All  or  reduced  7,  concentra-  It is a  Y e l l o w S. caused  intensity  This  by c h a n g e s i n  investigated at t h i s  time.  ( 2 0 ° C . 1 2°.)'.  DATA.  drawn t o the d e n s i t y c u r v e s  t h i r t e e n p e r m i t t e d dyes.  data  This i s notably  measurements were made a t r o o m t e m p e r a t u r e  Attention is f i r s t  t o some  Thus t h e  the s h a d e and  of the p r o b l e m , n a m e l y v a r i a t i o n s  ANALYSIS OF  con-  solutions.  dyes a r e q u i t e changed.  not  the  d i s t i l l e d water.  other than  changes i n s o l v e n t s was  that  i n calculating  tame o f Orange I , H r y t h r o s i n e and N a p h t h o l feature  be  the a b o v e c o n c e n t r a t i o n s .  o f unknown s i m p l e The  Brilliant  part i n  These are c l a s s i f i e d  for the  according to  colour. Plate 1 Blue.  Both  shows the  two  blue dyes,  t h e s e d y e s have v e r y  I n d i g o t i n e and  simple  a b s o r p t i o n maximum i n t h e r e d - o r a n g e . Brilliant Indigotine  Blue  occurs at  i s a t 611  640  millimicrons.  The  two  is  a further  to note  that  The  one  main  maximum d e n s i t y f o r  m i l l i m i c r o n s , while that  d i s t i n g u i s h e s between t h e s e of i n t e r e s t  curves with  Brilliant  for  spectrophotometer  dyes w i t h the utmost distinct  ease.  difference  the d e n s i t y c u r v e s o f t h e s e d y e s o c c u r s i n t h e r a n g e  300  It in  milli-  9.  Page m i c r o n s t o 440 m i l l i m i c r o n s . Plate dyes;.  As  chemical  2 illustrates one  the d e n s i t y c u r v e s  might expect  nature,  these  from  their  f o r the  similarity  t h r e e dyes have v e r y  maxima l o c a t e d v e r y c l o s e t o g e t h e r .  F a s t G r e e n , and  Although  these  fic,  the  and  simple  are  solution.  dilutions  o f 1/100,000 I n s t e a d  employed f o r t h e Plate  5 shows the  a b s o r p t i o n i n the v i s i b l e FCF  producing  microns  -490  able i n this is  yellow  part of  curve with  millimicrons.  the  two  Thus t h e s e  in  each other.  T h i s , then,  and  is  proper-  dyes show s t r o n g Yellow  two  t h e r a n g e 470 dyes  are  r e g i o n , and  dyes.  Orange milli-  indistinguish-  from  curves run "counter"  i s t h e r a n g e to s e a r c h orange  (Despite i t s  F o r t u n a t e l y , however,  t o 5 1 1 m i l l i m i c r o n s the  of these  Guinea  m i l l i m i c r o n s and  a " p l a t e a u " over  p a r t of t h e i r range.  either  in  o f 1/2^,000  spectrum, Sunset  s t r o n g a b s o r p t i o n i n the u l t r a v i o l e t  identify  speci-  were u s e d  dyes.  These l a t t e r  millimicrons  to  that both  an orange dye,  maximum a b s o r p t i o n a t 480  I a rather f l a t  654  dyes.  is really  c l a s s e d w i t h Orange I.)  very  to d i s t i n g u i s h  of t h e d i l u t i o n  o r a n g e and  F0F  with  Green.  are  v e r y i n t e n s e d y e s , and  other eleven  name, S u n s e t Y e l l o w ly  difficult  Zt i s noteworthy to repeat  F a s t Green are  curves,  627 m i l l i m i c r o n s  c l o s e f o r r o u t i n e work, t h e y  G r e e n and  and  T h e s e maxima o c c u r a t  at 6 2 1 m i l l i m i c r o n s f o r Guinea  t h r e e dyes are not  green  i n colour  similar  m i l l i m i c r o n s f o r L i g h t Green SF Y e l l o w i s h , a t for  three  i f one  there 250 to  wishes  Page 10, The density curves for the two yellow dyes, Tartrazine and EFaphthol S show a most unusual s i m i l a r i t y throughout the range 200 millimicrons to 700 millimicrons and would be very d i f f i c u l t to d i s t i n g u i s h .  However, Naphthol Yellow S has the property of  decolourizing almost completely i n d i l u t e mineral acid (say 2%f ) 0  and therefore i t s density curve should change r a p i d l y with changing pH. It is the intention of the writer to investigate the effects of changes i n hydrogen i o n concentration on the absorption curves of these and other dyes. I t remains to discuss the four red dyes, of which the absorption curves are shown i n Plate 4,  I t i s seen at once  that Erythrosine shows a double maximum at 528 millimicrons and 522 millimicrons, with a d i s t i n c t dip at 525 millimicrons. This double absorption maximum i s unique amongst the  thirteen  dyes tested, and i s a splendid identifying factor for Erythrosine. Amaranth shows a single maximum at J?21 millimicrons and can be readily i d e n t i f i e d .  However the maxima for Ponceau SX and  Ponceau 5R are only two millimicrons apart, namely at 504 m i l l i microns and 502 millimicrons respectively, and reference must be made to the u l t r a v i o l e t region,  Here i t is seen that  whereas Ponceau SX shows a d i s t i n c t minimum at 2 58 millimicrons and a maximum at 505.5 millimicrons, Ponceau 5R shows a m i n i mum at 506 millimicrons and a steeply r i s i n g curve from about 280 millimicrons to the lower l i m i t of the  spectrophotometer.  Hence i n the region 220 millimicrons -530 millimicrons the two  Page Ponceau curves r u n c o m p l e t e l y The  q u e s t i o n now  photometer would  11. counter  t o each  a r o s e as t o how  other.  successfully  the s p e c t r o -  be a b l e t o d e t e c t t h e p r e s e n c e  of  relatively  s m a l l amounts o f p e r m i t t e d d y e s i n t h e p r e s e n c e  of  larger  quantities permit  o f a second,  of (2  x 13  only possible mixtures.  x 12)  312  to attempt  Since  difficult  masking, dye.  binary mixtures  runs  experience  or i m p o s s i b l e t o  has  shown t h a t  separate  of  the  few  dyes it  of t h e s e  was  312  certain mixtures  the  are  solvent-partition  f o r . a n a l y s i s , and  to demonstrate  binary mixtures  c o n s t i t u e n t are  w h i c h c o u l d be illustrated  any p o s s i b l e  classified  some o t h e r s  shortcomings.:  surprising  these p o i n t s , of t h i s  and  will  Since  poor.  Guinea  These  are  G r e e n i s a. c o n -  not  f o r Guinea  630  Green i s  millimicrons, i t  Further  a peak i s not by any 7.  G r e e n and  634  s h o w i n g a peak between  millimicrons.  i n Plate  expected  distinguishing  G r e e n i s 621  the m i x t u r e  p o i n t that  f o r Guinea  show any  the "peak" f o r L i g h t  to f i n d  i s offered  shown c u r v e s  that  namely a t  important  diagnostic  that  6.  the  of s e p a r a t i o n s  Green S F Y e l l o w i s h i t i s t o be  the two  Recalling  millimicrons i s not  of  G r e e n SF Y e l l o w i s h as  as r e l a t i v e l y  i n P l a t e s 5 and  a mixture  features;.  with l i g h t  generally illustrative  g e n e r i c dye w i t h L i g h t that  thirteen  s p e c t r o p h o t o m e t r i c method.  The major  as l i k e l y  by  the  of t h i s type  on r e l a t i v e l y  method t h e s e were n a t u r a l l y c h o s e n were c h o s e n  Since  illustration means  H e r e , on a l a r g e  scale,  are  F a s t Green i n c o n c e n t r a t i o n  Page 12. of 1/100,000.  At the bottom of Plate 7 i s shown the curve for  a mixture of equal parts of each dye i n concentration of 1/3,004 000.  I t is clear that t h i s l a t t e r i s a simple curve with  a maximum at the expected wave-length (624 millimicrons) and with no suggestion that i t is not the curve of a definite compound.  This misleading s i m p l i c i t y of many curves produced  by mixtures i s a condition to be judged with extreme caution. The curve for Naphthol Yellow S i n Light Green SF Yellowi s h shows l i t t l e modification of the major curve except at 236 millimicrons - 250 millimicrons, where the Naphthol Yellow mixture curve i s at variance with the Light Green curve. Referring to Plate 6, Amaranth shows a d i s t i n c t though small i n f l e c t i o n at 521 millimicrons ( i t s absorption maximum), while the Erythrosine mixture shows a d i s t i n c t maximum at 525 millimicrons.  Uhese two red dyes are e a s i l y determined i n ten  percent, mixtures with Light Green SF Yellowish. Plate 8 shows five binary mixtures with Sunset Yellow FCF as the major constftuent (ninety percent.). i l l u s t r a t e two important points.  These curves  The f i r s t i s that i f the  minor constituent i s absorbed strongly i n a region where the major constituent shows l i t t l e or no absorption, then the curve for the mixture closely follows that of the d i l u t e d pure dye present to the smaller degree.  This fact i s shown i n the  curves for the three green dyes and f o r B r i l l i a n t Blue, The second important point i s i l l u s t r a t e d i n the ourve for the mixture of Erythrosine i n Sunset Yellow FCF.  Here,  Page  despite  the f a c t  that  13.  the curve c l o s e l y  Sunset Yellow FCF, n e v e r t h e l e s s  follows  the u n i q u e  the p a t t e r n f o r  ( f o r these  dyes) p r e s e n c e o f t h e d o u b l e maximum o f E r y t h r o s i n e itself,  and c l e a r l y i d e n t i f i e s E r y t h r o s i n e  thirteen  asserts  a s the m i n o r  constit-  uent • The value.  data  i n Plates  9 and 10 a r e o f p a r t i c u l a r  T a r t r a z i n e i s t h e d y e m o s t commonly f o u n d  because o f i t s y e l l o w concentration  that  colour,  i s o f t e n present  t h e o t h e r admixed dyes.  small  the  concentration  strong  quantity,  i twill  drive  i t into  the amyl a l c o h o l .  small  q u a n t i t i e s of I n d i g o t i n e ,  definitely unsuccessful  maximum f o r I n d i g o t i n e ) tion,  this separation  concentrations  Tartrazine,  proved  i n Tartrazine  The  s o l u t i o n i n curve  hue, y e t t h e d e n s i t y  curve  success.  Three  are i l l u s t r a t e d . i n nine of  a n d ( c ) i s one i n f i f t y .  one p a r t o f d y e i n  (c) i s q u i t e  presence of I n d i g o t i n e ,  separation i s  However, b y  of Indigotine  (b) i s one i n t w e n t y - f i v e ,  s o l u t i o n s u s e d were  with  a t 611 m i l l i m i c r o n s ( t h e  t o be a s i g n a l  (a) i s one p a r t  All  greenish  methods.  true  T a r t r a z i n e shows p r a c t i c a l l y no a b s o r p -  of Indigotine  I n P l a t e 10, c u r v e  a n d l o s t by  a c i d required to  and t h i s l a t t e r  since  greater  and p r e s e n t i n  This i s notably  by c h e m i c a l  means o f t h e s p e c t r o p h o t o m e t e r ,  i n much  be d e s t r o y e d  of h y d r o c h l o r i c  i n foods, and,  Moreover, i f the  admixed dye i s o f t h e t r i p h e n y l m e t h a n e t y p e , relatively  practical  yellow,  25,000 with  parts  o f water.  no v i s i b l e  shows u n m i s t a k a b l y the  Page  As (Plates  expected 9 and  14.  the t h r e e g r e e n d y e s a n d  10)  Brilliant  a r e e a s i l y d e t e c t e d when p r e s e n t  Blue with  Tartrazine. P l a t e 11 t h e g r e e n and  illustrates b l u e dyes  t h e ease w i t h which  the presence  of  i s d e t e c t e d when m i x e d w i t h e v e n a  n i n e - f o l d c o n c e n t r a t i o n o f Amaranth, Plate  12  demonstrates  cal  significance.  was  brought  present. without dye. and  As  to  The  A  an i n t e r e s t i n g  sample  of grape-coloured boiled  the l a b o r a t o r y f o r a n a l y s i s p u r p l e dye  apparent  passed  completely  of  a final  test mixtures  of food colours through  the  scheme pure  o f Amaranth w i t h B r i l l i a n t  o f A m a r a n t h w i t h I n d i g o t i n e were made t o m a t c h , by  t h r e e s o l u t i o n s were t h e n shows a t e l l t a l e at e x a c t l y  "break"  prepared. i n the  t h e same w a v e l e n g t h  known I n d i g o t i n e - A m a r a n t h doubt t h a t t h e tine i n a large It  mixture.  eye,  the  glance at P l a t e of  the dye  the  12  being  tested  i n f l e c t i o n p o i n t of  the  Thus i t i s shown b e y o n d of a l i t t l e  Indlgo=  q u a n t i t y of Amaranth.  spectrophotometer  many d y e - m i x t u r e s  t h e n , i n the l i g h t will  be  The  particularly  of t h i s r e s e a r c h ,  of great value i n  w h i c h u n t i l now  to a n a l y s e .  investigation,  A  curve as  Blue  D e n s i t y curves of  "unknown" m u s t be a m i x t u r e  seems c l e a r ,  impossible  practi-  candies  change, and gave a l l s i g n s of b e i n g a  the c o l o u r of t h e "unknown" s o l u t i o n .  the  experiment  writer along  identifying  have been d i f f i c u l t proposes  or  to c o n t i n u e  the f o l l o w i n g  that  lines:  this  15  Page  (1) A  study o f the dynamics of the d e n s i t y  curves  of the v a r i o u s m i x t u r e s , with a view to e s t a b l i s h i n g a s p e c i f i c scheme of a n a l y s i s f o r t h e i r  identity.  (2) Q u a n t i t a t i v e measurements of the should  be r e l a t i v e l y easy i n simple  d i f f i c u l t i e s when two  This  s o l u t i o n s , but w i l l  or more dyes are present  (5) A study o f the  dyes.  present  together,  v a r i a t i o n s i n the d e n s i t y  brought about by changes i n pH.  There i s every reason'to  b e l i e v e that s e v e r a l of the m i x t u r e s at present d i f f i c u l t d e f i n e may  be r e s o l v e d i n t h i s  curves  to  way.  REFERENCES  (1) "Methods of A n a l y s i s of the A s s o c i a t i o n of  Official  A g r i c u l t u r a l Chemists", S i x t h E d i t i o n , 194-5. Chapter (2); Holmes, W.C.;  Scanlan,  J.T.;  Peterson,  A.R.;  "The  XXI.  Visual  Spectrophotometry of Dyes." (United S t a t e s Department of A g r i c u l t u r e , T e c h n i c a l B u l l e t i n No.  510,  June, 1952.)  ERRATA (with reference  to P l a t e s )  to be read  "^nfl"  (1) The  a b s c i s s a u n i t s are  for "millimicrons"  (2) The  o r d i n a t e s c a l e s are i n " d e n s i t y " u n i t s , i . e . , the  l o g a r i t h m of the r e c i p r o c a l of the percentage  transmission.  / 4  BLUE  i  DYES.  Plote I  3.0brilliant blue  20-  .0-  30TTp GREEN  DYES.  Rate 2  light green SF yellowish  YELLOW  3.0-  & ORANGE DYES.  P  |  a t e  3  sunset yellow  naphthol yellow S. orange I.  20-,  1.0-  200 u  400 RED DYES. .ponceau 3R  600  erythrosine  ponceau SX  1.5-  1.0-  0.5amaranth  200 p  400  600  Plate 4  18  »  LIGHT GREEN & 1 0 % BINARIES  p,  dte  5  GUINEA GREEN  &  F A S T GREEN.  Plate 7  iast green .80guineo: greer .55^  .30-  5 0 % mixture  600M  620  640  SUNSET YELLOW & 10% BINARIES. sunset yellow  'erythrosine I.O-y  brilliant blue  Plate8  2L0-&.  TARTRAZINE and 10% BINARIES.  P l a t e  9  TARTRAZINE, BRILLIANT BLUE & INDIGOTINE. Plate 10  450 p  550  AMARANTH & 10% BINARIES. Plate 11 1.5  amaranth  brilliant blue fast green light green I 450 u  650 GRAPE COLOUR MIXTURES. Plate 12  0.6T  0.4-  "unknown"  brilliant blue with amaranth  0.2-  580 p  620  660  a 2..  SUBJECT TO THE ACT OR REGULATIONS THE FOLLOWING COLOURS MAY BE USEU IN OR UPON FOOU N a t u r a l Colours, being c o c h i n e a l and vegetable colour e x t r a c t i v e s A r t i f i c i a l Colours, being caramel and s p e c i a l l y p u r i f i e d vegetable and sugar charcoals, Coal Tar Dyes, being AMARANTH, the t r i s o d i u m s a l t of 1-(4-sulpho-l-naphthylazo)-2-naphthol-3, 6-disulphonic a c i d ; PONCEAU 3R, the disodium salt of l-pseudocumylazo-2-napththol-3, b-disulphonic a c i d , the b o i l i n g range of the crude, pseudocumidine obtained by r e d u c t i o n o f which s h a l l be between 220"C and 245°C; ERYTHROSINE, the disodium s a l t of 9-o-carboxyphenyl-6-hydroxy-2, 4 , 5 , 7 - t e craiodo-3-isoxanthone; PONCEAU SX, the disodium s a l t of 2-(5-sulpho-2, 4-xylylazo)-1-naphthol4-sulphonic a c i d ; OIL RED X0; l - x y l y l a z o - 2 - n a p h t h o l , o f which the x y l i d i n e obtained by i t s r e d u c t i o n s h a l l contain not more than 30.0 per cent of m-xylidine, and 95 per cent of such x y l i d i r a s h a l l d i s t i l between 212°C and 232°C; ORANGE 3. t h e mono sodium s a l t of 4-p-sulphophenylazo-l-naphthol; ORANGE .SS, l - o - t o l y l a z o - 2 - n a p h t h o l ; NAPHTHOL YELLOW S, the disodium or dipotassium s a l t of 2 , 4 - d i n i t r o l-naphthol-7-sulphoniC' a c i d , that s h a l l not contain more than 0.03 per cent o f Martius Yellow; OIL YELLOW AB,  l-phenylazo-2-naphthylamine;  OIL YELLOW OB, l-o-tolylazo-2-naphthylamine; TARTRAZINE, The t r i s o d i u m s a l t o f 3-carboxy-5-hydroxy-l-p-sulphophenyl-4-p-sulphophenjilazopyrazole; SUNSET. YELLOW FCF, the disodium s a l t of-l-p-sulphophenylazo-2-naphthol6-sulphonic a c i d ; LIGHT GREEN S.F. YELLOWISH, the disodium s a l t of 4-( (4-(N-ethyl-psulphobenzylamino)-phenyl)) (4-sulphoniumphenyl)-methylene) -(l-(N-ethyl-N-p-sulphobenzyl)-delta 2 , 5 , - cyclohexadienimine: GUINEA GREEN B, the monosodium s a l t of 4-(4-(N-ethyl-p-sulpho-benzylamino) -diphen^rl-methylene )-(l-(N-ethyl-N-p-sulphoniumbenzyldelta 2 , 5 , cyclohexandienimine); FAST GREEN FCF, the disodium s a l t of 4-((4-N-ethyT-p-sulphobenzylamino)phenyl)-(4-hydroxy-2-sulphoniumphenyl)-methylene)-(1(N-ethyl-N-p-sulphobenzyl) delta 2 , 5 , cyclohexadienimine); INDIGOTINE, the disodium s a l t of indigotine--5,5 -disulphonic a c i d ; 1  BRILLIANT BLUE FCF, the disodium s a l t of 4-((4-N-ethyl-p-sulphobenzylamino)-phenyl) - (2-sulphoniumphenyl).- methylene) (l-fN-ethyl-N-p/sulphobenzyl) - d e l t a 2 , 5 , cyclohexadienimine).  

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