Use of the triiodide–hexadecylpyridinium chloride micellar system for the kinetic determination of tungsten (VI)

Abstract

The associate formed by triiodide ion and hexadecylpyridinium chloride (cetylpyridinium chloride (CPC)) micelles was used to enhance the kinetic spectrophotometric determination of W VI by its catalytic action on the oxidation of iodide with hydrogen peroxide in an acidic medium. The reaction was monitored spectrophotometrically by measuring the increase in absorbance of I 3 −–CPC associate at 525 nm by the fixed-time method of 3 min from initiation of the reaction. The micellar medium allowed the determination of W VI at concentrations between 4 and 90 ng ml −1 with a detection limit of 2.4 ng ml −1 (i.e. about 12–13 times lower than those of methods implemented in aqueous media). The relative standard deviation for nine replicate analyses was 0.03% for 76.6 ng ml −1 of W VI. The proposed method was applied to the determination of W VI in aqueous extracts of soil sample with no prior separation.