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

A novel and versatile method for the determination of Th-232, U-234, U-235 and U-238 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 U-235 and U-238 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(-1) U-235 and 65 ng g(-1) U-238. The results of the external calibration were in good agreement with the IDMS results and overlapped within their uncertainties. Th-232 was quantified to about 30 ng g(-1) (solid material) by on-line HPIC-ICP-SFMS using U-233 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.