Quantitative in situ microanalysis of minor and trace elements in biogenic calcite using infrared laser ablation -: inductively coupled plasma mass spectrometry:: a critical evaluation

This study evaluates the possibilities and limitations of infrared laser ablation - inductively coupled plasma mass spectrometry, using (43)Ca as internal standard and the silicate glass reference materials NIST 610/612 as calibration standards, for quantifying the spatiotemporal variations of Mg, Mn, Sr, Ba and Pb in the calcite layer of Mytilus edulis shells. It demonstrates that the ablation behaviour of Ca relative to those of the analytes is dependent on the ablation time and substrate matrix (inorganic and biogenic calcite versus NIST 610/612); however, for ablation times less than or equal to 80 s, internal standardization with Ca improves precision to <10% relative standard deviation (RSD) for all tested substrates. Variations in the Ca distribution in the studied shells are shown to be comparable to this precision, implying that we can assume a constant Ca concentration. When using NIST 610/612 as calibration standards for the analysis of inorganic calcite, an accuracy better than 10% and a precision <8% RSD (not evaluated for Pb) are obtained for ablation times less than or equal to 40 s. For shell calcite a comparable reproducibility is obtained (<11% average difference between overlapping analysis series) but since no homogeneous shell reference material is available the accuracy cannot be determined. Experimental results indicate that for certain instrument operating conditions accuracy could be deteriorated by differences in ablation characteristics between samples and standards, so that matrix matching is preferable. Owing to the lack of a matrix matched standard for the analysis of shell calcite, we decided to use NIST 610/612 as standards and to assure intercomparability of our results by normalizing all data with respect to one selected shell. (C) 1999 Elsevier Science B.V. All rights reserved.