Optimization of electrochemical hydride generation coupled to microwave-induced plasma atomic emission spectrometry for the determination of arsenic and its use for the analysis of biological tissue samples

Abstract

Argon and helium MIPs operated in a surfatron and in a TE₁₀₁ resonator were coupled to an electrochemical HG cell for the determination of As by AES. The optimization of this new type of HG used for the direct introduction of AsH₃ into the plasma, included variations of the microwave power, sample flow rate, acid flow rate, acid concentration, gas flow rate and current in the electrochemical flow cell. Compared with chemical HG using NaBH₄, the detection limits for As could be improved by a factor of two. The best detection limit (3σ) for As was achieved with the Ar MIP operated in a surfatron (1 ng ml^–1). It was also shown that interferences of transition metals and of other hydride forming elements are lower than with classical HG. The TE₁₀₁ resonator, which shows better stability and less interferences than the surfatron, was connected to a Pd-coated graphite furnace for preconcentration of the AsH₃ by hot trapping at temperatures of between 50 and 200 °C. The transient As signal has good reproducibility (6%) and with preconcentration times of 1 min the detection limit for As is 25 pg ml^–1. With a set-up combining electrochemical flow cell HG, preconcentration in a Pd-coated graphite furnace and MIP-AES using a TE₁₀₁ resonator, reliable determinations of As in various digested biological samples at the 0.05–10µg g^–1 level could be performed.