Flow-injection and stopped-flow completely continuous flow spectrophotometric determinations of aniline and cyclohexylamine

The sequential determination of aniline and cyclohexylamine using flow-inje ction analysis and their simultaneous kinetic determination with a stopped- flow completely continuous flow (stopped-flow CCF) system are proposed. Bot h methods are based on the reaction of these amines with 1,2-naphthoquinone -4-sulfonate (NQS) for two measurement conditions: (i) under selectivity co nditions for one of the analytes (aniline) and (ii) under non-selective rea ction conditions in which both amines react simultaneously with NQS. The pH enabled both amines to be distinguished in the flow-injection method, whil e the difference in reaction rates of the two derivatives was exploited adv antageously in the stopped-flow method. Therefore, aniline was directly qua ntified under selective conditions, whereas the determination of cyclohexyl amine involved the calculation of its net analyte response. The figures of merit (sensitivity, linear range, detection limit and precision) of both me thods were established. Several mixtures of aniline and cyclohexylamine wer e quantified using both flow-injection and kinetic methods. The overall pre diction errors of the flow-injection method were 1.6% and 4.9% for aniline and cyclohexylamine, respectively. The accuracy of the kinetic procedure in the analysis of synthetic samples was 2.1% and 5.4% for aniline and cycloh exylamine, respectively. The method was applied to the determination of ani line and:cyclohexylamine in commercial sweeteners. A good agreement between the proposed and the standard methods was found. (C)1999 Elsevier Science B.V. All rights reserved.