Overestimation of orthophosphate monoesters in lake sediment by solution 31P-NMR analysis.

Solution 31P nuclear magnetic resonance spectroscopy (31P-NMR) is a useful method for analyzing organic phosphorus (Po). Unfortunately, the extraction conditions, which are highly alkaline and require long extraction times, make this analysis less effective. In this research, according to the lability of orthophosphate monoesters (mono-Po) and orthophosphate diesters (diesters-Po), we verified the hypothesized overestimation of mono-Po in lake sediment using solution 31P-NMR. We set three scenes to redistribute the mono-Po and diesters-Po. Six components, including eight mono-Po species, were detected in the NaOH-EDTA extracts of sediment samples using 31P-NMR. The results showed that mono-Po (212.7 mg kg-1) was the dominant Po in the surface sediment. In the three scenes, mono-Po decreased from 212.7 to 112.0 mg kg-1, and diesters-Po increased from 31.9 to 132.7 mg kg-1. The ratio of mono-Po to diesters-Po increased from 6.7 to 0.8. Therefore, we deduced that the concentration of mono-Po was overestimated, while that of diesters-Po was underestimated, in most research because of the high pH and long extraction process. Diesters-Po might be an important labile P source during the P "exhausted" period.