Determination of multiple element/calcium ratios in foraminiferal calcite by quadrupole ICP-MS Jimin Yu, Jason Day, Mervyn Greaves, and Henry Elderfield Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK (jyu02@esc.cam.ac.uk) [1] A method has been developed for rapid and precise simultaneous determination of nine element/Ca ratios in foraminiferal tests directly from intensity ratios using external, matrix-matched standards on a quadrupole inductively coupled plasma – mass spectrometer (ICP-MS). All quantification isotopes are determined in pulse mode to avoid cross-calibration. Small argide ( 40 Ar 26 Mg) interferences on 66 Zn are corrected by using two additional Mg and Zn standards. A stable signal, conducive for high-precision measurements, is obtained by cone conditioning. Variable calcium concentration has negligible effect on Li, Al, Mn, and Sr, but Ca concentrations for standards and samples need to be constrained at a similar level for precise measurements of Zn, Cd, and U. Aliquots of samples are first analyzed for Ca concentrations on an inductively coupled plasma–atomic emission spectrometer (ICP-AES), and the remaining solutions are diluted to Ca concentration of 100 ppm for ratio measurements to assure data quality. The long-term reproducibility of the method yielded precisions of Li/Ca = 2.4%, B/Ca = 4.2%, Mg/Ca = 1.4%, Al/Ca = 14%, Mn/Ca = 0.9%, Zn/Ca = 2.8% (1.27.8 mmol/mol) and 5.1% (0.51.2 mmol/mol), Sr/Ca = 0.9%, Cd/Ca = 2.4% (0.070.24 mmol/mol) and 4.8% (0.010.07 mmol/mol), and U/Ca = 2.5% for foraminiferal samples as small as 60 mg. Components: 5324 words, 2 figures, 4 tables. Keywords: inductively coupled plasma – mass spectrometry; element/calcium ratios; foraminifera; calcite. Index Terms: 4875 Oceanography: Biological and Chemical: Trace elements (0489); 4924 Paleoceanography: Geochemical tracers; 4994 Paleoceanography: Instruments and techniques. Received 9 March 2005; Revised 2 June 2005; Accepted 28 June 2005; Published 30 August 2005. Yu, J., J. Day, M. Greaves, and H. Elderfield (2005), Determination of multiple element/calcium ratios in foraminiferal calcite by quadrupole ICP-MS, Geochem. Geophys. Geosyst., 6, Q08P01, doi:10.1029/2005GC000964. ———————————— Theme: Development of the Foraminiferal Mg/Ca Proxy for Paleoceanography Guest Editor: Pamela Martin 1. Introduction [2] The chemical composition of foraminiferal calcite accumulating in deep sea sediments has been widely used to reconstruct chemical or phys- ical properties in ancient oceans [e.g., Boyle, 1988; Elderfield and Ganssen, 2000; Marchitto et al., 2000; Hall and Chan, 2004]. Large differences in the abundance of chemical constituents of forami- niferal calcite have required element ratios in foraminiferal shells to be determined by a combi- nation of different methodologies and instrumen- tation [e.g., Boyle, 1981; Boyle and Keigwin, 1985; Marchitto et al., 2000]. Because elements are analyzed sequentially in solutions of different dilutions by different methods, the approaches are usually time-consuming and not always conducive to high-precision ratio determinations. Simulta- neous generation of element ratios has the advantage of reducing overall sample size requirements and G 3 G 3 Geochemistry Geophysics Geosystems Published by AGU and the Geochemical Society AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Geochemistry Geophysics Geosystems Technical Brief Volume 6, Number 8 30 August 2005 Q08P01, doi:10.1029/2005GC000964 ISSN: 1525-2027 Copyright 2005 by the American Geophysical Union 1 of 9