Hexadecylpyridinium chloride micelles for the kinetic determination of sulphur-containing compounds by their induction of the iodine-azide reaction

Abstract

The potential use of the association formed by triiodide ion and hexadecylpyridinium chloride (cetylpyridinium chloride, CPC) for the determination of sulphur-containing compounds, which act as inductors for the iodine-azide reaction was investigated. Triiodide ion interacts with CPC cationic micelles, which results in maximum absorption at 500 nm in addition to a substantially increased absorptivity and stability constant of the triiodide complex. The micellar medium allows the determination of reduced glutathione, tetramethylthiuram disulphide and ethylenebis-dithiocarbamic acid (zineb) in the ranges (2–10) x 10 −7 M, (8−63) x 10 −9 M and 40−450 ng ml −1, respectively, with detection limits (3σ) for the three inductors of 0.7 x 10 −7 M, 5.4 x 10 −9 M and 32 ng ml −1, respectively. The presence of the surfactant allows one to determine lower concentrations of tetramethylthiuram disulphide, reduced glutathione and zineb by factors of 51, 32 and 2.5 respectively, relative to the aqueous medium. The proposed method has been applied to the determination of reduced glutathione in whole blood samples and to the fungicide tetramethylthiuram disulphide present in a commercial formulation used in agriculture.