CHEMICAL AMPLIFICATION METHOD FOR THE DETERMINATION OF CHROMIUM AT TRACE LEVELS

A highly sensitive spectrophotometric method for the determination of 40-400 ng of chromium(III) is described. This is based on the oxidatio n of chromium(III) with potassium periodate in alkaline medium to form chromate and iodate. After masking the excess periodate using ammoniu m molybdate at pH 3, the formed iodate was treated with iodide and aci d to generate iodine. The iodine was extracted into benzene and was st ripped to aqueous phase by equilibrating the organic layer with sodium sulphite solution. The stripped iodide was oxidised to iodate by brom ine water and the excess bromine was destroyed using sulphosalicylic a cid. The formed iodate was used to generate nitrite on treatment with hydroxylamine. The generated nitrite was determined by diazo coupling reaction with p-nitroaniline and NEDA. The azo dye has an absorption m aximum at 545 nm (epsilon = 7.8 x 10(5) L mol(-1)cm(-1)) and the coeff icient of variation is 3.2% for ten determinations of chromium at the 300 ng level. Selectivity was achieved by prior extraction of chromium (VI) species as chromyl chloride into methyl isobutyl ketone. Chromyl chloride tvas stripped back into sodium sulphite solution and after bo iling off the excess SO2 with acid chromium(III), was determined.