Direct Determination of Tellurium in Geological Samples by Inductively Coupled Plasma Mass Spectrometry Using Ethanol as a Matrix Modifier

Abstract

Direct determination of tellurium in geological samples by inductively coupled plasma mass spectrometry (ICP-MS) is often complicated by its low abundance, poor analytical sensitivity, and the presence of xenon interferences. Therefore, a simplified and rapid method for direct determination of nanogram levels of tellurium in geological samples using ICP-MS by reduction of interferences and improvement of sensitivity was developed. It is impossible to resolve ¹²⁶Te and ¹²⁸Te from isotope interferences of Xe even by currently available high-resolution magnetic mass spectrometry due to the extremely small mass difference (0.001–0.002 amu). However, the addition of 4% ethanol was found to suppress the interferences of Xe by a factor of 6 and increases the sensitivity of Te determination in ICP-MS by a factor of 3 relative to the values obtained in conventional 3% (v/v) HNO₃ solution at the corresponding optimum operating conditions, respectively. The detection limits of ¹²⁶Te and ¹²⁸Te were reduced by a factor of 7.2 and 8.8, respectively, and the limit of quantitation (LOQ) for ¹²⁶Te in the presence of 4% ethanol was 1.5 ng g⁻¹ (the LOQ is expressed as the concentration in the solid samples, thereby taking into account the dilution factor of 1000). The agreement between the determined Te concentration values (r = 0.998) in various geological samples (n = 140) by using isotopes of ¹²⁶Te and ¹²⁸Te indicates negligible contributions of polyatomic interferences produced by the addition of ethanol at these m/z. The proposed method was successfully applied to the direct determination of nanogram levels of Te in a series of international geological reference materials.