Method for phosphate oxygen isotopes analysis in water based on in situ enrichment, elution, and purification
The phosphate oxygen isotope (δ 18 O P ) ratio has been proven to be an effective tool to trace the sources and biogeochemical cycles of phosphorus (P) in aquatic ecosystems . However, the enrichment of phosphate (PO 4 ) and the removal of impurities are quite complex and easy to cause PO 4 loss in current δ 18 O P analytical methods. Moreover, the δ 18 O P value obtained by the commonly-used instantaneous sampling method is more of the instantaneous information of P, which is accidental or uncertain for accurate identification of the P source. In this study, a new method of in situ enrichment, elution, and purification of PO 4 (ISEEP) was developed for δ 18 O P analysis in waters. This method utilized a PO 4 binding phase (Zr-Oxide gel) to selectively in situ adsorb PO 4 in water and exhibited an adsorption capacity per unit area of up to 789.3 μg P/cm 2 . The PO 4 on the gel was eluted easily with a 1 M NaOH solution. More than 99.7% of the common anions, cations, and dissolved organic matter (DOM), as well as more than 90% of the trace elements were removed synchronously after adsorption and elution of PO 4 . The recovery rate of PO 4 in the whole procedure was as high as 92.8%. The XRD and SEM examinations showed that the ISEEP can obtain high-purity Ag 3 PO 4 solid for the δ 18 O P measurement. The reliability of the ISEEP method is confirmed by the measured δ 18 O P value and standard deviation of parallel samples from different types of natural waters obtained by both the ISEEP and the current popular McLaughlin (2004) method. It provides a good prospect of this new method for tracing the P sources and their biogeochemical cycling in aquatic ecosystems.
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