Abstract

Hydride generation, sequestration in graphite tubes and simultaneous multi-element measurement by atomic absorption spectrometry were used for determination of Sb(V), Bi(III), Se(IV), As(III) and As(V) in Millipore or brackish water by a method based on batchwise addition of the samples to a reaction vessel. As the reducing agent, NaBH₄ was added at a controlled flow rate. A statistical programme, Modde 4.0, capable of multivariate optimisation of working parameters for the multi-element determination, was used to optimise the concentrations of HCl, the amount of NaBH₄, purge gas flow rates, the graphite atomiser's deposition temperature, as well as the temperature of the reaction vessel.

In general, the concentrations of HCl and the amount of NaBH₄ had the greatest impact on the response and several of the working parameters showed interactions. For highest sensitivity different parameters had to be used for the two matrices. Optimum parameter settings in Millipore and brackish water were: concentration of HCl 2.1 and 2.7 mol l⁻¹, respectively; 2% NaBH₄ addition during 120 s (4 ml) or 84 s (2.8 ml), respectively; Ar purge gas flow rate 150 ml min⁻¹ in both matrices; reaction vessel temperature 16 and 0 °C, respectively; and a deposition temperature of 600 and 150 °C, respectively. The detection limits were restricted by variations in the blank absorbance. For 2 ml of sample the detection limits in brackish water were 17, 14, 25 and 140 ng l⁻¹ for As, Se(IV), Bi and Sb, respectively.