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

Abstract

We report a new method for HR-ICP-MS based accurate and precise B/Ca determination from low mass natural carbonates (≤5 µg 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 2.0 ± 1.0 µmol/mol, internal precision ≤1.0%, average within run external precision ≤4.0% (2σ), and rapid sample analysis (60 samples/day) make the method well suited for routine measurements. Established methods of B/Ca determination require ≥65 µg CaCO3 to achieve a comparable external precision of 3.5% (2σ). We report a B/Ca detection limit of 2 µmol/mol compared to ≥10 µmol/mol for previous methods, a fivefold improvement. The method presented here can determine a wide range of B/Ca (9.0–250 µmol/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, ∼85, and ∼200 µmol/mol of B/Ca are ±3.7% (2σ, n = 100), ±3.9% (2σ, 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 µg CaCO3. This method is suitable for trace element analysis of single foraminifera shells.