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

摘要

The oxygen isotope ratio in phosphate (delta 18OP) is an effective tool for tracing the sources of phosphorus (P) and their biogeochemical cycles. The HCl-extractable inorganic phosphate (HCl-PTI) 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 delta 18OP composition of HCl-PTI due to the significantly interference of large amounts of Fe2+/3+, Ca2+, Cl- and other impurities in the HCl-PTI extracts. In this study, we developed a simple and promising purification method for delta 18OP analysis of HCl-PTI in sediments and soils based on the superior selective enrichment and elution abilities of phosphate (PO4) and efficient synchronous removal of impurities by Zr-Oxide gel in highly acidic HCl-PTI extract. The enrichment rate and elution rate of PO4 in the HCl-PTI 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 HClPTI extract. It's indicated that the purity of the Ag3PO4 solid for delta 18OP composition analysis of HCl-PTI could reach 99.9%. The above results show that the new method is very simple, efficient and reliable for the delta 18OP analysis of HCl-PTI 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.