KINETIC DETERMINATION OF ANTIMONY(III) BASED ON ITS ACCELERATING EFFECT ON THE REDUCTION OF 12-PHOSPHOMOLYBDATE BY ASCORBIC-ACID IN A MICELLAR MEDIUM

The nonionic surfactant Triton X-100 was used as a micellar medium to develop the reduction of 12-phosphomolybdate to a blue heteropoly compound by ascorbic acid. Antimony(III), which accelerates this reaction in aqueous media by the formation of a mixed heteropoly compound with molybdenum and phosphorus, Is concentrated on the micellar surface, thereby augmenting its effective concentration in the reaction medium. The micellar catalysis of Triton X-100 permits the kinetic-photometric determination of antimony(III) over the linear range 0.1-1.8 mg/L with a detection limit ot 0.07 mg/L, i.e. 7 times lower than that of the corresponding method developed in an aqueous medium. The relative precision for 0.8 mg/L antimony was 1.8%. Significantly improved selectivity was also obtained. Thus, ions such as arsenate and silicate are tolerated at concentrations 10- and 1000-fold. respectively, of that of antimony. Some observations on the mechanism via which Triton X-100 acts on the reaction are made.