Analysis of Geological Materials for Bismuth, Antimony, Selenium and Tellurium by Continuous Flow Hydride Generation Inductively Coupled Plasma Mass Spectrometry

Abstract

A study was made of mutual interferences in the determination of Bi, Sb, Se and Te by hydride generation inductively coupled plasma mass spectrometry (HG–ICP-MS). The design of the study was based upon the valency states in which these elements would occur following two acid digestion procedures commonly used for geological materials ( aqua regia and HF–HClO ₄ –HNO ₃ –HCl), that is, as Bi ^III , Sb ^V , Se ^IV and Te ^IV . Arsenic in its two valency states (III and V) was also examined as a potential interferent but Ge, Sn and Pb were not, as formation of their hydrides at the concentration of HCl used (2–4 m) would be negligible. Interferents were investigated at concentrations up to 2000 µg l ^-1 while the analyte concentration was held at 0.2 µg l ^-1 . As ^V and Se ^IV severely suppressed the signal for Te in both 2 and 4 m HCl, though less so in the stronger acid medium. These interferences were negated by reduction of As ^V to the non-interfering state As ^III and Se ^IV to Se ^O by addition of KI and ascorbic acid at a final strength of 0.005%. The preferred acid medium was selected as 4 m HCl for two reasons: interferences were reduced; and wash-out time between samples was shorter ( i.e. , decreased memory effect). Mutual interferences of possible concern comprise the effect of: 2500-fold excess of Bi on the measurement of Te; a 5000-fold excess of Te on Bi; a 2500-fold excess of Bi on Sb; and a 5000-fold excess of Bi on Se. However, these relative abundances in geological materials (rocks, sediments, soils, vegetation) would be extraordinary and hence implementation of the recommended scheme should produce analysis for Bi, Sb, Se and Te by HG–ICP-MS that is free of mutual interference.