Routine Analyses of Trace Elements in Geological Samples using Flow Injection and Low Pressure On‐Line Liquid Chromatography Coupled to ICP‐MS: A Study of Geochemical Reference Materials BR, DR‐N, UB‐N, AN‐G and GH

Abstract

We describe analytical procedures for trace element determinations developed at the CNRS Service d'Analyse des Roches et des Minéraux (SARM) and report results obtained for five geochemical reference materials: basalt BR, diorite DR‐N, serpentinite UB‐N, anorthosite AN‐G and granite GH. Results for rare earth elements, U and Th are also reported for other reference materials including dunite DTS‐1, peridotite PCC‐1 and basalt BIR‐1. All rocks were decomposed using alkali fusion. Analyses were done by flow injection ICP‐MS and by on‐line low pressure liquid chromatography (LC)‐ICP‐MS for samples containing very low REE, U and Th concentrations. This latter method yielded limits of determination much lower than data by direct introduction and eliminated possible isobaric interference on these elements. Although results agree with most of the working values, when available, results for some elements differed slightly from the recommended concentrations. In these cases, we propose new values for Co, Y and Zn in basalt BR, Zr in diorite DR‐N, Sr and U in granite GH, and Ga and Y in anorthosite AN‐G. Furthermore, although the Sb concentration measured in AN‐G was very close to our limit of determination, our value (0.3 ± 0.1 μg g−1) is much lower than the reported working value of 1.4 ± 0.2 μg g−1. These new values would need to be confirmed by a new inter‐laboratory programme to further characterise these reference materials. Results obtained for REE, Th and U concentrations using the on‐line low pressure LC‐ICP‐MS yielded good limits of determination (ng g−1 to sub‐ng g−1 for rocks and ng l−1 to sub‐ng l−1 for natural waters) and accurate results. The efficiency of the matrix separation allowed accurate measurements of Eu without the need to correct the BaO isobaric interference for samples having Ba/Eu ratios as high as 27700. For REE concentrations in PCC‐1 and DTS‐1, differences with values reported in the literature are interpreted as resulting from possible heterogeneity of the reference materials. Thorium and U values are proposed for these two samples, as well as for AN‐G and UB‐N.