A Novel Method to Determine the Carbon Isotopic Composition of Inositol Hexaphosphate (Phytate) in Soil by Gas Chromatography-Combustion-Isotope Ratio Mass Spectrometry.

Rationale: Understanding the decomposition of inositol hexaphosphate (phytate), the dominant form of organic phosphorus (OP) in soil, is vital for studying phosphorus (P) cycling in terrestrial ecosystems. However, the lack of multiple stable P isotopes complicates the study of phytate dynamics under natural conditions and over long periods.
Methods: A novel method is presented to determine the carbon isotopic composition of inositol in phytate using compound-specific isotope analysis. For this purpose, phytate was extracted from soil and purified via ion exchange chromatography, followed by dephosphorylation, derivatization, and analysis using GC-MS and GC-C-IRMS. Pure compounds were also analyzed to assess protocol efficiency, identify isotopic fractionations, and apply isotopic corrections due to derivatization.
Results: Phytate extracted from soil samples was identified using GC-MS chromatograms. Replicate analyses of the pure compounds indicated that the protocol is highly reproducible. The carbon isotopic composition (δ ¹³ C) showed a high reproducibility, with values varying by less than 0.5‰ and with no detectable isotopic fractionation during sample preparation. The δ ¹³ C values of phytate in soil samples reflected the dominant vegetation type (C ₃ or C ₄ ) growing at the study site.
Conclusions: This study offers a novel approach of determining δ ¹³ C values of inositol of phytate in environmental samples, offering new opportunities to investigate and quantify OP dynamics based on stable carbon isotopes.
(© 2025 The Author(s). Rapid Communications in Mass Spectrometry published by John Wiley & Sons Ltd.)