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.