Determination of niobium, tantalum, zirconium and hafnium in geological materials by extraction chromatography and inductively coupled plasma mass spectrometry

A novel method is described for the determination of Nb, Ta, Zr and Hf at low levels in geological materials by inductively coupled plasma mass spectrometry. The method involves the group separation of the four analytes by extraction chromatography using N-benzoyl-N-phenylhydroxylamine (BPHA) supported on a microporous polymeric resin. Samples were decomposed by hydrofluoric acid (HF) dissolution followed by treatment with HClO4 fuming to remove fluoride. LiBO2 fusion for sample dissolution can also be used for Nb, Zr and Hf, but significantly low Ta results were observed. Ta results were significantly improved when the quenching solution contained a small amount of BF to prevent hydrolytic loss. This study also revealed that Teflon materials showed relatively high blank values and/or memory effect for Zr and Ta. Calibration of ICP-MS is carried out with artificial solutions, using internal standardisation with Y-89 and Rh-103 for Zr-90 and Nb-93, and Tm-169. and Re-185 for Hf-177, Hf-178 and Ta-181. The limits of quantitative determination (LQD) are 30, 16, 3, 6 ng/g for Zr, Nb, Hf and Ta, respectively, for 0.1 g sample. The results for replicate analyses of international basaltic rock standard materials demonstrate good precision and accuracy of the proposed method. (C) 2002 Elsevier Science B.V. All rights reserved.