Determination of As, Cd, Pb and Tl in coal by electrothermal vaporization inductively coupled plasma mass spectrometry using slurry sampling and external calibration against aqueous standards

Abstract

A method was developed for the determination of As, Cd, Pb and Tl by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) with slurry sample introduction using certified reference coal samples. The 75As, 111Cd, 208Pb and 205Tl isotopes were monitored, considering the lower probabilities of these isotopes in suffering interferences. The carrier and modifier effect of Ru added in solution was evaluated, demonstrating that sensitivity for all elements is considerably improved by the addition of 15 µg of Ru to each individual measurement. This confirms its ability to act as a physical carrier particularly for the analytes in aqueous solution. Pyrolysis and vaporization temperatures of 500 and 2500 °C, respectively, were selected after optimization for aqueous solutions and for coal slurries. Similarly, the carrier gas flow rate was optimized as 1.1 L min−1. After optimization of the operational parameters, the determination of the four elements in six certified reference coal samples was carried out by external calibration against aqueous standards in 5% v/v HNO3, resulting in good agreement between the certified or given values and the determined ones. For Tl, due to the absence of certified values, a comparison was established considering previously published data using solid sampling high-resolution continuum source graphite furnace atomic absorption spectrometry. Detection limits (µg g−1) of 0.1, 0.004, 0.045 and 0.001 were achieved for As, Cd, Pb and Tl, respectively, and the precision was typically better than 10%.