Feasibility of As, Sb, Se and Te determination in coal by solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry

Abstract

In this work, a method for the determination of As, Sb, Se and Te in mineral coal was developed using solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry (SS-ETV-ICP-MS). The following operational parameters of the ETV-ICP-MS system were evaluated: the furnace temperature program, the mass of Ir used as the modifier, the oxygen flow rate (used in the pyrolysis step) and carrier and bypass gas flow rates. The possibility of using calibration with aqueous standard solutions was also investigated. Calibration using aqueous standard solutions was feasible for As, Sb and Te determination, and calibration using certified reference materials (CRMs) of coal was required for Se determination. For comparison of the results, coal samples were decomposed by microwave-assisted wet digestion to obtain reference values for As and Sb by ICP-MS and Se by collision/reaction cell technology inductively coupled plasma mass spectrometry (CRC-ICP-MS). In addition, samples were digested by microwave-induced combustion to obtain reference values for Te by ICP-MS. No statistical difference was observed between the results by SS-ETV-ICP-MS and those obtained by ICP-MS (As, Sb and Te) or CRC-ICP-MS (Se) after sample digestion. Additionally, CRMs of coal (NIST 1632b, NIST 1632c and NIST 1635) were analysed by SS-ETV-ICP-MS, and the results were in agreement with the certified values. The limit of quantification was 0.03, 0.01, 0.03 and 0.006 μg g⁻¹ for As, Sb, Se and Te, respectively. These values were lower than those obtained by other methods and allowed the determination of analytes at trace and ultra-trace levels. The SS-ETV-ICP-MS method for coal presented other advantages, such as minimization of the sample preparation step, minimization of the use of large amounts of reagents and suitability of accurate determination of those analytes commonly susceptible to limitations using conventional methods.