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The determination of micromolar concentrations of ammonia with 1-fluoro, 2:4-dinitrobenzene Gadsby, Peter James

Abstract

The conversion of ammonia to 2:4-dinitroaniline by reaction with 1-fluoro, 2:4-dinitrobenzene and the subsequent conversion of dinitroaniline to a diazo-dye with N-(1-naphthyl)ethylenediamine has been investigated as an analytical method for determining ammonia at the micromolar concentration level. Particular emphasis was placed upon the possibility of applying this method to the analysis of sea water. Dinitroaniline was formed under alkaline conditions (pH greater than 8) and required the presence of the fluoro-dinitrobenzene as a separate phase for initiation of the reaction. The conversion, which was light sensitive, was accelerated by increases in pH and temperature, but neither of these factors improved the final yield. The yield of dinitroaniline had a marked dependence on the amount of fluorodinitrobenzene; initially increasing with increasing fluorodinitro-benzene content, it then decreased with higher fluorodinitrobenzene concentrations suggesting further reaction between dinitroaniline and fluorodinitrobenzene. In both distilled and sea water, the maximum yield of dinitroaniline from solutions containing ammonia at the micromolar concentration level was found to be 55-58%. The absorbance of the diazo-dye in sea water of salinity 30.4% was only 42% of that observed in distilled water. Although sufficiently sensitive for application to sea water analysis, the precision of the conversion of dinitroaniline to the diazo-dye in sea water was poor compared to that achieved in distilled water.

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