Measurement of the Isotopic Composition of Molybdenum in Geological Samples by MC-ICP-MS using a Novel Chromatographic Extraction Technique

A novel preconcentration method is presented for the determination of Mo isotope ratios by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) in geological samples. The method is based on the separation of Mo by extraction chromatography using N-benzoyl-N-phenylhydroxylamine (BPHA) supported on a microporous acrylic ester polymeric resin (Amberlite CG-71). By optimising the procedure, Mo could be simply and effectively separated from virtually all matrix elements with a single pass through a small volume of BPHA resin (0.5ml). This technique for separation and enrichment of Mo is characterised by high selectivity, column efficiency and recovery (similar to 100%), and low total procedural blank (similar to 0.18ng). A Mo-100-Mo-97 double spike was mixed with samples before digestion and column separation, which enabled natural mass-dependent isotopic fractionation to be determined with a measurement reproducibility of <0.09 (Mo-98/95, 2s) by MC-ICP-MS. The mean Mo-98/95(SRM) (3134) (NIST SRM 3134 Mo reference material; Lot No. 891307) composition of the IAPSO seawater reference material measured in this study was 2.00 +/- 0.03 parts per thousand (2s, n=3), which is consistent with previously published values. The described procedure facilitated efficient and rapid Mo isotopic determination in various types of geological samples.