Developing a new method for analyzing carbonate-associated phosphate through inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS)

Abstract

Phosphorus, a critical biogeochemical element regulating marine productivity, poses analytical challenges in carbonate matrices using conventional spectrophotometric methods. This study establishes novel analytical protocols employing inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS) with oxygen reaction mode and argon gas dilution (AGD)-ICP-MS/MS for simultaneous quantification of carbonate-associated phosphate (CAP) and rare earth elements plus yttrium (REE + Y). Through systematic optimization, we implemented a 2% v/v acetic acid partial leaching protocol for CAP extraction. Comparative evaluation of collision/reaction cell modes revealed that the triple quadrupole configuration with O₂ reaction gas mode (TQ-O₂) demonstrated superior interference elimination capabilities, particularly effective in resolving the [¹⁴N¹⁶O¹H]⁺ isobaric interference on ³¹P⁺ (with a mass shift to m/z 47 for [³¹P¹⁶O]⁺). The developed methods achieved detection limits of 0.15 μg L⁻¹ (ICP-MS/MS) and 2.56 μg L⁻¹ (AGD-ICP-MS/MS) for phosphorus, with good determination coefficient (R² > 0.999). Method validation using four geochemical certified reference materials (JDo-1, AGV-2, BHVO-2 and BCR-2) demonstrated excellent agreement with certified values. The CAP/(Ca + Mg) ratios for JDo-1, SRM 1d, and GBW07108 were determined to provide interlaboratory comparative information. This multi-parameter analytical framework provides enhanced throughput for paleoceanographic studies requiring coupled nutrient (P) and redox proxy (REE + Y) analysis.