Application of ion-exchanger phase absorptiometry to flow analysis. Determination of trace amounts of chromium(VI) in water

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Abstract
Ion-exchanger phase absorptiometry was applied to the determination of trace amounts of chromium(VI) in natural waters using flow analysis. The product of the reaction of chromium(VI) with 1,5-diphenylcarbazide was introduced into a carrier solution stream in the flow system. The increase in absorption by the coloured complex sorbed on a cation exchanger, with which the light-path of a flow-through cell had been partly filled, could be measured directly with high precision. When 4.4 cm3 of sample solution were pumped through, the sensitivity obtained was 160 times higher than that of the corresponding solution method. The detection limit was as low as 0.5 ng of chromium(VI). Cations such as calcium and background electrolytes present in natural waters at high concentrations caused a change in the background attenuation. For fresh water, this effect could be removed only by passing the sample solution through a small hydrogen-form cation-exchange column. For sea water, it is necessary to use a calibration graph prepared at similar concentrations to those in the sample solution. Without pre-concentration, the proposed method is directly applicable to the analysis of natural water samples containing chromium(VI) at less than 1 µg dm–3.

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