Inhibition of the palladium-catalysed reaction between cobalt(III)-ethylenediaminetetraacetate and hypophosphite. Kinetic determination of cysteine, N-acetylcysteine and cystine
Abstract
A kinetic method for the determination of cysteine, N-acetylcysteine and cystine based on their inhibitory effect on the palladium(II)-catalysed reaction between the cobalt(III)-ethylenediaminetetraacetate (EDTA) complex and the hypophosphite ion is proposed. The reaction is monitored spectrophotometrically at 540 nm. The influence of reaction variables and the interfering effect of major amino acids was studied. Under the selected experimental conditions (2.6 × 10–3M CoIII-EDTA, pH 3.2 adjusted with Britton-Robinson buffer, 0.4 M H2PO2–, 10.3 or 23.5 µM PdII and a temperature of 20 ± 0.2 °C), these three amino acids were determined in the range 0.16–16.7 µM. The method was applied to the determination of N-acetylcysteine in pharmaceutical preparations.