A single-step purification method for the precise determination of the antimony isotopic composition of environmental, geological and biological samples by HG-MC-ICP-MS

Abstract

Antimony isotopes have been recently used as geochemical tracers for archeological or environmental purposes. The purification of antimony in samples with a low Sb concentration and a complex matrix is a critical step to measure the ¹²³Sb/¹²¹Sb ratio by hydride generation coupled to a multi-collector inductively coupled plasma mass spectrometer (HG-MC-ICP-MS). A single-step purification method based on the use of thiol-functionalized mesoporous silica powder (TSP) was developed to separate antimony from other elements. A low amount of Sb (40–100 ng) is required thanks to low procedural blanks (<1 ng Sb) and an efficient removal (98.7% on average) of potential interfering elements (including As, Cd, Co, Cr, Cu, Fe, Ni, Pb, Se, and Sn). The method was validated on fourteen Certified Reference Materials (CRMs) including environmental materials (sediments and soils), biological materials (plants, human blood and urine), rocks and anthropogenic materials (fly ash, road dust and polyethylene). Antimony was recovered at 100 ± 7% and no isotopic fractionation occurred during the procedure. The isotopic composition of Sb (δ¹²³Sb) in the CRMs ranged between −0.52 ± 0.06‰ (2 sd) and 0.40 ± 0.03‰ (2 sd) relative to an in-house isotopic standard solution (SPEX). The external reproducibility was evaluated at 0.05‰ (2 sd) for δ¹²³Sb, based on replicated measurements of independently digested and purified CRMs. CRMs GSD-3, SDO-1 and BCR-176R exhibited δ¹²³Sb values similar to previous measurements by Rouxel et al. (2003). In addition, three pure standard solutions of Sb were measured against the in-house isotopic standard solution. Two of them were isotopically similar (δ¹²³Sb = 0.00 ± 0.05‰, Sb Fisher Scientific® and PlasmaCAL-1, SCP Science®), while a δ¹²³Sb value of 0.62 ± 0.02‰ was measured for the third one (PlasmaCAL-2, SCP Science®). This raises the importance of choosing a common isotopic standard solution to compare already published and future Sb isotope data.