Method for analyzing the oxygen isotope composition of HCl-extractable inorganic phosphate in sediments and soils

The oxygen isotope ratio in phosphate (δ 18 O P ) is an effective tool for tracing the sources of phosphorus (P) and their biogeochemical cycles . The HCl-extractable inorganic phosphate (HCl-P TI ) is the primary component of P and plays a key role in the dynamic transformation of P in sediment and soil. However, it has always been difficult to purity sample for analyzing the δ 18 O P composition of HCl-P TI due to the significantly interference of large amounts of Fe 2+/3+ , Ca 2+ , Cl − and other impurities in the HCl-P TI extracts. In this study, we developed a simple and promising purification method for δ 18 O P analysis of HCl-P TI in sediments and soils based on the superior selective enrichment and elution abilities of phosphate (PO 4 ) and efficient synchronous removal of impurities by Zr-Oxide gel in highly acidic HCl-P TI extract. The enrichment rate and elution rate of PO 4 in the HCl-P TI extract by the Zr-Oxide gel could achieve 100% respectively, and the synchronous removal rates of most anions, dissolved organic carbon (DOC), metals, and trace elements could be above 96% respectively, reducing the tedious operation of conventional methods and the difficulties in removal of impurities, such as Cl − in HCl-P TI extract. It's indicated that the purity of the Ag 3 PO 4 solid for δ 18 O P composition analysis of HCl-P TI could reach 99.9%. The above results show that the new method is very simple, efficient and reliable for the δ 18 O P analysis of HCl-P TI in sediments and soils. This study provides new methodological support for identifying the sources of P and tracing their biogeochemical cycles in sediment or soil environment.