Kinetic-potentiometric determination of amino acids based on monitoring their reaction with dinitrofluorobenzene using a fluoride-selective electrode

Abstract

A kinetic-potentiometric method is described for the determination of amino acids, dopa and aspartame, based on monitoring their reaction with 2,4-dinitrofluorobenzene using a fluoride-selective electrode at pH 9.0 and 25 °C. Initial-slope and fixed-time (60 s) methods were used to construct calibration graphs, in most instances in the range 1 × 10^–4–5 × 10^–3M. Binary mixtures of cysteine-cystine can be determined at pH 8 and 9. Dopa and aspartame were determined in commercial formulations with a precision and accuracy of 2–3% without interference from excipients or coloured or turbid solutions. The method is very simple and rapid. Reaction constants and orders of reaction were experimentally determined for various amino acids.