Comparison of the techniques of atomic absorption spectrometry and inductively coupled plasma mass spectrometry in the determination of Bi, Se and Te by hydride generation

Abstract

This study compares the performance of hydride generation quartz tube atomic absorption spectrometry (HG-QTAAS) and inductively coupled plasma mass spectrometry (HG-ICP-MS) in the determination of Bi, Se and Te in 38 geological reference materials (GRMs). Samples are decomposed in aqua regia and analytes separated from potential liquid-phase interferents (e.g., Cu, Ni, Co) by coprecipitation with La(OH) 3. Method detection limits using HG-QTAAS are 10 ng g −1 for all three elements and are improved using the more sensitive HG-ICP-MS, to 1 ng g −1 for Bi and Te, and 6 ng g −1 for Se. Results for Bi by both techniques compare well, with typical relative standard deviations (RSD) of 3–4% for the triplicate digestions and analyses of the GRMs. For the most part, results are also in agreement for Se but diverge for those samples where As is present in excess over Se by about 150-fold. In these cases, mutual interference by As suppresses the Se signal in measurement by HG-QTAAS. Mutual interferences in HG-QTAAS are worse for the element of lowest natural abundance, Te. In the presence of As at 300-fold excess, recovery of the Te signal is only 50%. In the drainage sediment GSD-6 which contains As at 13.6 μg g −1, the value for Te by HG-QTAAS is as low as 68 ng g −1 compared to that by HG-ICP-MS of 157 ng g −1 and a proposed literature value of 140 ± 40 ng g −1. An excess of 120-fold of Se IV also reduces the Te signal by 50%, but this is of less concern given the relative levels of As and Se in geological materials and can be negated in any case by preferential reduction to the non-reactive Se 0 with a small amount of KI. The only mutual interference warranting attention in determination of these elements by HG-ICP-MS is that of As V on Te where an excess of As of 5000-fold can suppress the Te signal by 35%. This can be negated by reduction to the non-interfering As III by addition of KI (to a concentration of 0.005%) prior to analysis. Thus, HG-ICP-MS is clearly the preferred method for the determination of Te, with precision typically at 5–7% RSD at levels of Te above 10 ng g −1. Analysis of a subset of 16 GRMs using the mixed-acid attack, HFHClO 4HNO 3HCl, demonstrates that while aqua regia can be expected to result in full recovery for Bi, it provides incomplete digestion for some sample matrices for Se and, to a greater extent, for Te.