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

The sequential determination of aniline and cyclohexylamine using flow-injection analysis and their simultaneous kinetic determination with a stopped-flow completely continuous flow (stopped-flow CCF) system are proposed. Both methods are based on the reaction of these amines with 1,2-naphthoquinone-4-sulfonate (NQS) for two measurement conditions: (i) under selectivity conditions for one of the analytes (aniline) and (ii) under non-selective reaction conditions in which both amines react simultaneously with NQS. The pH enabled both amines to be distinguished in the flow-injection method, while the difference in reaction rates of the two derivatives was exploited advantageously in the stopped-flow method. Therefore, aniline was directly quantified under selective conditions, whereas the determination of cyclohexylamine involved the calculation of its net analyte response. The figures of merit (sensitivity, linear range, detection limit and precision) of both methods were established. Several mixtures of aniline and cyclohexylamine were quantified using both flow-injection and kinetic methods. The overall prediction 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 cyclohexylamine, respectively. The method was applied to the determination of aniline and cyclohexylamine in commercial sweeteners. A good agreement between the proposed and the standard methods was found.