Data for: Oxygen Isotope Analyses of Phosphate and Organophosphorus Compounds by Electrospray Ionization Orbitrap Mass Spectrometry

Orbitrap mass spectrometry with electrospray ionization (ESI-Orbitrap MS) enables 18O/16O ratio measurements in phosphate and organophosphorus compounds. Its use for studying metabolic processes that involve phosphoryl transfer reactions and mitigation of organophosphorus pollutants is therefore of particular interest. While the instrumental feasibility of such 18O/16O ratio measurements has been shown, the applicability of such analyses in aqueous matrices on multi-purpose mass spectrometers remains unaddressed. Here, we (i) evaluated the interplay between instrument parameters and the long-term accuracy and precision of ESI-Orbitrap MS for the determination of δ18O(PO4) from H2PO4- vs. PO3- fragments of phosphate, (ii) identified properties of sample solutions that are critical for accurate and precise measurements, and (iii) propose a sample purification procedure for elimination of matrix-based interferences. In ten measurement campaigns over two years, we found a long-term reproducibility of δ18O(PO4) within ± 2.8‰. Results of in-source fragmentation experiments of H2PO4- to PO3- show excellent agreement in δ18O and offer promising opportunities to probe for 18O/16O ratios in organophosphorus compounds. By investigating the effect of the aqueous matrix and interfering anions on 18O/16O ratio measurements, we found that a water content exceeding 50 vol-\% and the presence of oxyanions such as nitrate and sulfate limit measurement accuracy due to interferences of matrix constituents in the ESI source. To overcome these challenges, we evaluated selective phosphate extraction with zirconium-based metal--organic framework (MOF) as sorbent. The resulting purification procedure enabled the successful extraction and recovery of phosphate from nitrate and sulfate-containing aqueous solutions, resulting in methanolic phosphate samples that enabled accurate analyses of δ18O(PO4) by ESI-Orbitrap MS.