Abstract:

Spectrophotometric determination of carboxylic acids in aqueous solutions has been developed based on the formation of hydroximic acid from carboxylic acid in the presence of hydroxylamine perchlorate(HAP) and dlcyclohexylcarbodiimide(DCC) as well as the formation of purple ferric hydroxamate from hydroximic acid in the presence of acidic ferric perchlorate solution. We have investigated the effects of acidity, concentration and addition volume of ferric perchlorate, concentration and addition volume of DCC and HAP, and reaction temperature and reaction time on the absorbance. The results illustrate that this reaction has the largest absorbance under the follow conditions: conditions of reaction: 1.0 mL of 0.068 7 mol/L HAP， 0.5 mL of 0.6 mol/L DCC, after shaken, incubation of reaction mixture for 15 min at room temperature; conditions of pigmentation:0.02 mol/L acidic ferric perchlorate solution(0.3 mol/L perchloric acid). Working curves of n-butyric, n-valeric and benzoic acid have also been investigated, which indicate that this method is simple, easy to use, precise, and has a wide linear range. It can be applied to those carboxylic acids which are difficult to extract from aqueous solutions, and the application of this method for the determination of various kinds of acids in the eluate after chromatographic separation are expected to be advantageous.

Key words: carboxylic acid,dlcyclohexylcarbodiimide,hydroxylamine perchlorate,hydroxamate,ferric hydro xamate,spectrophotometry