Precise multielemental ratios in small foraminiferal samples determined by sector field ICP-MS



Inductively coupled plasma mass spectrometry (ICP-MS) holds two main advantages over other techniques for the measurement of foraminiferal elemental ratios: (1) numerous trace metals may be precisely and simultaneously measured, and (2) smaller samples may theoretically be used. Methods are presented for the precise determination of Mg/Ca, Sr/Ca, Cd/Ca, Zn/Ca, Li/Ca, U/Ca, Mn/Ca, and Fe/Ca by sector field ICP-MS. Analytical precision is largely independent of sample size over the range of ∼5 to 125 μg CaCO3, eliminating the need for narrow target dilutions. Long-term 1σ precisions are as follows: Mg/Ca = 0.54%, Sr/Ca = 0.57%, Cd/Ca = 1.8%, Zn/Ca = 3.2%, Li/Ca = 0.88%, U/Ca = 1.9%, Mn/Ca = 0.97%, and Fe/Ca = 1.4%. For Mg/Ca, actual foraminiferal samples appear to give reliable results below 10 μg CaCO3 (postcleaning mass).