Determination of multiple element/calcium ratios in foraminiferal calcite by quadrupole ICP-MS



[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 (40Ar26Mg) interferences on 66Zn 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 μmol/mol) and 5.1% (0.5∼1.2 μmol/mol), Sr/Ca = 0.9%, Cd/Ca = 2.4% (0.07∼0.24 μmol/mol) and 4.8% (0.01∼0.07 μmol/mol), and U/Ca = 2.5% for foraminiferal samples as small as 60 μg.