Chemical speciation of chromium(III,VI) employing extractive spectrophotometry and tetraphenylarsonium chloride or tetraphenylphosphonium bromide as ion-pair reagent

A simple and accurate extractive spectrophotometric procedure for the chemical speciation of chromium(III,VI) species in aqueous media has been developed. The method is based upon the extraction of the complex ion-associate formed between the chloro chromate (CrO3Cl−) anion and the ion-pair reagent tetraphenylarsonium chloride (TPAs+Cl−) or tetraphenylphosphonium bromide (TPP+Br−) at pH ≤ 0 in chloroform followed by direct spectrophotometric measurement at 355 nm. The optimum concentration range evaluated by Beer-Lambert's law, Ringbom's plot, the molar absorptivity, the Sandell's sensitivity, the extraction and stability constants (KD, Kex and β), the stoichiometry and the extraction equilibria of the produced complex ion-associates have been determined and gave a convenient applications of the investigated system for analytical purposes. Chromium(III) was also determined by the proposed procedure after prior oxidation to chromate with H2O2 in alkaline solution. The method has been applied successfully for the analysis of chromium(VI) and total chromium(III,VI) in industrial wastewater of electroplating plant.