Determination of Hg and Tl in environmental reference materials using slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry with permanganate as modifier and calibration against aqueous standards

Abstract

A method for the determination of Hg and Tl in environmental samples by slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry is proposed. The slurry is prepared by mixing the sample, ground to a particle size of ≤50 µm, with 5% v/v nitric and 1% v/v hydrofluoric acids in an ultrasonic bath, and leaving it to stand for 40 h before analysis. The slurry was homogenized in the autosampler cup with a constant flow of argon, just before transferring an aliquot to the graphite furnace. Potassium permanganate in solution, in an untreated and a Ru-treated tube, as well as potassium and manganese in solution were studied as modifiers and carriers. Best thermal stabilization and sensitivity were obtained with KMnO₄ in an untreated tube, especially for Tl. These conditions were adopted, together with the optimized pyrolysis temperatures of 300 °C for Hg and 500 °C for Tl, and a vaporization temperature of 1000 °C for both analytes. The accuracy of the method was assured by the analysis of eight certified reference materials, using external calibration with aqueous standards prepared in the same medium as the slurries. The limits of detection in the samples were 0.18 µg g⁻¹ for Hg and 0.07 µg g⁻¹ for Tl. The precision found for the different samples, expressed as relative standard deviation, was 0.8–11% for Hg and 1–9% for Tl (n = 3).