Direct determination of trace elements in austenitic stainless steel samples by ETV-ICPOES

Abstract

Electrothermal vaporization (ETV) coupled to inductively coupled plasma optical emission spectrometry (ICPOES) was applied to the direct analysis of austenitic stainless steel powders using external calibration with increasing amounts of urban particulate matter (NIST 1648a) certified reference material. The method was first validated through the analysis of a reference material of free cutting steel, BCS 152/3, which was also analysed, following digestion in aqua regia, by ICPOES with external calibration using matrix-matched standard solutions. A four-step heating program, where the 30 s vaporization step was not ramped and followed a cooling step after pyrolysis, was used along with hemi-spherical graphite boats and trifluoromethane (CHF₃, freon R-23) reaction gas, which resulted in sharp analyte signal peaks. Internal standardization with an argon emission line (415.859 nm) was applied throughout to compensate for sample loading effects on the plasma, improve the signal-to-background ratio and extend the linear dynamic range. Quantification limits ranged from 0.02 (Cd) to 200 (Si) μg g⁻¹ in the solid using 5 mg aliquots, and are one or two orders of magnitude lower than those obtained by ICPOES with nebulization for several elements. The proposed method allowed determination of Al, Cd, Ce, Co, Cu, Mn, Pb, S, Si, Ti, V and Zn at levels in the 10 μg g⁻¹ to 0.4% (m m⁻¹) range, in agreement with results obtained by ICPOES following digestion. The method is suitable for alloy quality control, as it drastically reduces analysis time and cost by eliminating the acid digestion step altogether, which is quite attractive for industrial applications.