Application of a radially viewed inductively coupled plasma-optical emission spectrophotometer to simultaneous measurement of Mg/Ca, Sr/Ca, and Mn/Ca ratios in marine biogenic carbonates



[1] We developed and applied an analytical system for the simultaneous determination of magnesium/calcium, strontium/calcium, and manganese/calcium ratios in biogenic carbonates using a Perkin-Elmer 4300 Optima DV inductively coupled plasma-optical emission spectrophotometer in radial mode. Intensity ratio responses to calibration standard elemental ratios were linear over suitable working ranges. We evaluated instrumental response using solution replicates, and we analyzed planktonic foraminifera in multiple runs. Ca concentrations were kept in a relatively narrow range, typically ∼0.6–2.4 mM Ca, although we found no resolvable Ca matrix effect over a much wider range. Each analysis required a minimum sample volume of 300 μl and took 3.5 min instrument time. An analytical run of 30 samples plus standards, blanks, and control materials typically took ∼5–6 hours. Reproducibility (interrun precision, 1s %RSD) for solutions was 1.2%, 1.5%, and 1.2% for Mg/Ca, Sr/Ca, and Mn/Ca ratios, far smaller than reproducibility for foraminiferal replicates over multiple analytical runs. There was no independent reference material for assessing accuracy. Detection limits were equivalent for an 0.5 mM Ca solution to 0.058 mmol/mol for Mg/Ca, 0.015 mmol/mol for Sr/Ca, and ∼0.005–0.020 mmol/mol for Mn/Ca. Precautions included limiting length of time the peristaltic tubing for the autosampler was used, avoiding Mg contamination from plastic ware, and screening out results from samples with very low Ca concentrations (<0.25 mM Ca).