Determination of Y, Zr and ultra-low Nb concentrations in geological material by multi-ion counting spark-source mass spectrometry (MIC-SSMS)

Precise concentrations of Zr, Y and Nb in the mu g/g to ng/g range have been determined in rock samples using multi-ion counting spark-source mass spectrometry (MIC-SSMS). A high resolution method, combined with interference correction on Zr-91 and Nb-93 for low concentration samples, was applied. An analytical precision of 2-5% for concentrations down to 0.020 mu g/g and 10% for lower concentrations was attained. The detection limit is below 0.005 mu g/g.. By measuring international reference materials, the accuracy of the method was determined to be within about 10% of the recommended values. However, the accuracy of the final concentration is influenced by interference corrections, but the additional error is below 20%. The interference problem is most difficult for Al-rich samples (>15% Al2O3), as the interfering molecules an (CaAlC2+)-Ca-40-Al-27-C-12 and (Al3C+)-Al-27-C-12. The accordance between ICP-MS and MIC-SSMS results is worse for low Nb concentrations in the ng/g range. Here, ICP-MS gives systematically lower values than MIC-SSMS. The reason for this discrepancy is not yet clear, but may be caused by Nb loss during chemical treatment of the samples prior to ICP-MS measurements.