A new method for phosphate purification for oxygen isotope ratio analysis in freshwater and soil extracts using solid-phase extraction with zirconium-loaded resin.

Rationale: Phosphate (PO ) oxygen isotope (δ O ) analysis is increasingly applied to elucidate phosphorus cycling. Due to its usefulness, analytical methods continue to be developed and improved to increase processing efficiency and applicability to various sample types. A new pretreatment procedure to obtain clean Ag PO using solid-phase extraction (SPE) with zirconium-loaded resin (ZrME), which can selectively adsorb PO , is presented and evaluated here.

Methods: Our method comprises (1) PO concentration, (2) PO separation by SPE, (3) cation removal, (4) Cl removal, and (5) formation of Ag PO . The method was tested by comparing the resulting δ O of KH PO reagent, soil extracts (NaHCO , NaOH, and HCl), freshwater, and seawater with data obtained using a conventional pretreatment method.

Results: PO recovery of our method ranged from 79.2% to 97.8% for KH PO , soil extracts, and freshwater. Although the recovery rate indicated incomplete desorption of PO from the ZrME columns, our method produced high-purity Ag PO and accurate δ O values (i.e., consistent with those obtained using conventional pretreatment methods). However, for seawater, the PO recovery was low (1.1%), probably due to the high concentrations of F and SO which interfere with PO adsorption on the columns. Experiments indicate that the ZrME columns could be regenerated and used repeatedly at least three times.

Conclusions: We demonstrated the utility of ZrME for purification of PO from freshwater and soil extracts for δ O analysis. Multiple samples could be processed in three days using this method, increasing sample throughput and potentially facilitating more widespread use of δ O analysis to deepen our understanding of phosphorus cycling in natural environments.