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

Abstract 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 (CrO 3 Cl − ) 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 ( K D , K ex 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 H 2 O 2 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.