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

A simultaneous multi-element approach utilising "in-atomiser trapping" elec trothermal atomic absorption spectrometry (ETAAS) for As, Bi, Sb and Se was developed. The approach uses flow injection methodology and hydride format ion with sodium tetrahydroborate to sequestrate the hydrides of the element s of interest on an Ir pre-coated graphite tube. Since the efficiency of th e hydride formation depends on the oxidation state of the analyte, an off-l ine reduction process was included to ensure that the analyte to be determi ned was in the most sensitive and favourable oxidation state. Initially fiv e elements, As, Bi, Sb, Se and Te, were considered for simultaneous "in-ato miser trappin". The elements were split into two groups reflecting the natu re of the reducing agent required by each of the elements. Group A consiste d 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 agen t. However, Te was later removed from Group B due to problems in identifyin g a set of compromise conditions which enabled all three elements to be det ermined simultaneously. Bismuth featured in both groups as it did not requi re a reduction step. Various tube coatings were considered and Ir and Zr we re evaluated. Iridium was found to be well suited to this application. The characteristic masses obtained using this method were 177, 91, 107 and 90 p g for As, Bi, Sb and Se, respectively, yielding detection limits (500 mu l sample loop) of 0.82, 0.04, 0.26 and 0.29 mu g l(-1). Precision for analyte s at the 5 mu g 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.