Determination of B/Ca of natural carbonates by HR-ICP-MS

We report a new method for HR-ICP-MS based accurate and precise B/Ca determination from low mass natural carbonates (5 mu g CaCO3), utilizing a mixed acid matrix (0.1 M HNO3 and 0.3 M HF) and accurate matrix matching technique. Our procedural B/Ca blank of 2.01.0 mu mol/mol, internal precision 1.0%, average within run external precision 4.0% (2 sigma), and rapid sample analysis (60 samples/day) make the method well suited for routine measurements. Established methods of B/Ca determination require 65 mu g CaCO3 to achieve a comparable external precision of 3.5% (2 sigma). We report a B/Ca detection limit of 2 mu mol/mol compared to 10 mu mol/mol for previous methods, a fivefold improvement. The method presented here can determine a wide range of B/Ca (9.0-250 mu mol/mol) in mass limited samples with considerable tolerance for matrix matching efficiency (30%). The long-term reproducibility of B/Ca measured on Cambridge in-house consistency standards containing <20, approximate to 85, and approximate to 200 mu mol/mol of B/Ca are 3.7% (2 sigma, n=100), 3.9% (2 sigma, n=150), and +/- 3.2% (2 s, n =180), respectively. A host of other trace element to Ca ratios can also be determined at comparable external precision from samples containing 5 mu g CaCO3. This method is suitable for trace element analysis of single foraminifera shells.