Separation of spectral and non-spectral interferences by on-line high performance ion chromatography inductively coupled plasma sector field mass spectrometry (HPIC-ICP-SFMS) for accurate determination of 234U , 235U, 238U and 232Th in industrial ores

Abstract

A novel and versatile method for the determination of 232Th, 234U, 235U and 238U in milling grade ores and intermediates containing high amounts of rare earth elements (REE) was developed. Spectral and non-spectral interferences were eliminated by on-line matrix separation with high performance ion chromatography (HPIC) using 2,6-pyridinedicarboxylic acid (PDCA) as complexing agent. Hyphenation to inductively coupled plasma sector field mass spectrometry (ICP-SFMS) introduced a highly sensitive method of detection. Quantification of uranium and thorium could be established using external calibration and post-column internal standardization. Elemental levels down to concentrations of pg g−1 to ng g−1 in samples containing rare earth elements as the main matrix components could be assessed. The method was validated for 235U and 238U by comparison of isotope dilution mass spectrometry (IDMS) results without and with on-line matrix separation using a matrix matching pure cerite carbonate sample containing about 0.5 ng g−1235U and 65 ng g−1238U. The results of the external calibration were in good agreement with the IDMS results and overlapped within their uncertainties. 232Th was quantified to about 30 ng g−1 (solid material) by on-line HPIC-ICP-SFMS using 233U as internal standard. The results were in excellent agreement with those obtained by HPIC-ICP-SFMS using indium as internal standard. Measurement of a series of industrial samples proved the versatility of the method and can give a quick assessment of whether a material is suitable for a further production process or not, since isotope dependent limit values have to be determined.