Determination of toxic trace impurities in titanium dioxide by solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry

Abstract

This paper reports on the performance of solid sampling-electrothermal vaporization-inductively coupled plasma mass spectrometry (SS-ETV-ICPMS) for the direct multi-element determination of six toxic trace impurities (As, Cd, Hg, Pb, Sb and Zn) in three different TiO₂ samples. Careful selection of the most suitable target nuclides for the different analytes and temperature program optimization permit the reliable monitoring of the analytes of interest, while avoiding the occurrence of potentially relevant spectral interferences. A pyrolysis-free program, in which simultaneous vaporization of all the analytes is carried out at a relatively low temperature (1700 °C), was used. In this way, sample matrix and analyte co-vaporization is avoided, considerably reducing matrix effects and allowing the determination of Zn, which would otherwise be hampered by a spectral overlap with TiO⁺ ions. Calibration against aqueous standards was found to be feasible. Addition of 50 ng Pd as carrier agent improved the linearity of the calibration curves. Two different internal standards (¹⁰⁵Pd⁺ and ¹²⁵Te⁺) were used to compensate for matrix effects. The method thus developed exhibits interesting features: low limits of detection (ng g⁻¹ range) for all of the elements, at least an order of magnitude lower than those for digestion-based procedures; high sample throughput (maximum 35 min per determination), contrasting with the 2 h required for sample digestion and subsequent analysis; low sample consumption (a few milligrams only); precision values usually in the 9–13% RSD range; and last but not least, the absence of any sample pre-treatment, with the subsequent lower risk of analyte losses, contamination or personal and instrumental harms derived from the necessity of using hazardous reagents for sample digestion. SS-ETV-ICPMS therefore seems to be a promising alternative for industrial control analysis of TiO₂ samples with analyte contents ranging from a few ng g⁻¹ to several hundreds of µg g⁻¹.