Phosphorus is an essential nutrient for life, playing a role in various molecules and energy transfer in cells. It moves through the environment in biogeochemical cycles that transform and translocate phosphorus in soil, water, and living and dead organic material. The oxygen isotope composition (δ18O) of phosphate is a crucial tool for tracing biogeochemical phosphorus cycling.
However, the current methodologies for measuring this composition include tedious and time-consuming sample preparation, such as precipitating aqueous phosphate as silver phosphate (Ag3PO4). Besides challenging sample preparation, this method requires a large sample size and carries a risk of coprecipitation of other compounds like nitrate and dissolved organic compounds that can impact the quality of isotopic measurements.
A better way to analyze phosphate δ18O?
Is there a better, easier way to analyze phosphate δ18O? Lower your sample size with a new approach to phosphate isotope analysis.
A new study by Wang et al. (2024) presents a promising alternative. The research demonstrates the use of Thermo Scientific Orbitrap Electrospray Ionization Mass Spectrometry (ESI-Orbitrap-MS) for measuring the oxygen isotope composition of dissolved phosphate at nanomole level. This innovative method utilizes PO3 fragment ions to achieve comparable analytical precision to the conventional TC EA IRMS while using less than 1% of the sample amount.
Measuring phosphate δ18O using ESI-Orbitrap-MS methodology has been proposed by Neubauer et al. (2020), focusing on H2PO4– ions, however the results of the Wang et al. (2024) approach demonstrate that phosphate δ18O can be more reliably measured by the PO3− ions than by the H2PO4− ions. The authors highlight two main reasons:
- the H2PO4– (m/z = 97) can be interfered by the HSO4− (m/z = 97) that is often present at high concentrations in natural water samples, whereas P16O3− ions (m/z = 79) are not interfered with by 32S16O3− (m/z = 80) ions, and
- as PO3– fragment has no hydrogen, there is no need for high mass resolution mode (that is in H2PO4− ion measurements needed to separate H2P16O3 17O− and 2H1HP16O4−), resulting in higher analytical precision.
Wang et al. (2024) achieved a long-term accuracy of 0.8‰ (1 standard deviation) for phosphate δ18O under a dual inlet, direct liquid-phase injection condition by using two-magnitude smaller sample sizes (∼25 nmol) compared to the conventional IRMS method.
How can you expand your isotope research with this new, innovative workflow? Thermo Scientific Orbitrap Exploris Isotope Solutions comprises a dedicated sample introduction concept, distinctive method setup and a data evaluation framework to convert isotopologue intensities to accurate isotope ratios. Download the infographic for at glance overview of benefits of using this Orbitrap-based technology approach for deriving intramolecular isotopic information in biogeochemical research and beyond.
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