Simultaneous multi-element determination of hydride-forming elements by “in-atomiser trapping” electrothermal atomic absorption spectrometry on an iridium-coated graphite tube

Abstract

A simultaneous multi-element approach utilising “in-atomiser trapping” electrothermal atomic absorption spectrometry (ETAAS) for As, Bi, Sb and Se was developed. The approach uses flow injection methodology and hydride formation with sodium tetrahydroborate to sequestrate the hydrides of the elements of interest on an Ir pre-coated graphite tube. Since the efficiency of the hydride formation depends on the oxidation state of the analyte, an off-line reduction process was included to ensure that the analyte to be determined was in the most sensitive and favourable oxidation state. Initially five elements, As, Bi, Sb, Se and Te, were considered for simultaneous “in-atomiser trappin”'. The elements were split into two groups reflecting the nature of the reducing agent required by each of the elements. Group A consisted of As, Bi and Sb and used l-cysteine as the reducing agent, whilst Group B consisted of Bi, Se and Te and used concentrated HCl as the reducing agent. However, Te was later removed from Group B due to problems in identifying a set of compromise conditions which enabled all three elements to be determined simultaneously. Bismuth featured in both groups as it did not require a reduction step. Various tube coatings were considered and Ir and Zr were evaluated. Iridium was found to be well suited to this application. The characteristic masses obtained using this method were 177, 91, 107 and 90 pg for As, Bi, Sb and Se, respectively, yielding detection limits (500 µl sample loop) of 0.82, 0.04, 0.26 and 0.29 µg l ^–1 . Precision for analytes at the 5 µg l ^–1 level was typically better than 3.5% RSD. The method was validated by the analysis of two Certified Reference Materials and good agreement was found with the certified values.