Optimizing the Method for 31P-NMR Analysis of Organic Phosphorus from Wetland Sediments
LU Jin1, WANG Hai-wen2, HAO Hong1, GAO Bo1, JIA Jian-li2
1. China Institute of Water Conservancy and Hydropower Research, Beijing 100083, China 2. School of Chemical and Environmental Engineering, China University of Mining and Technology, Beijing 100083, China
Abstract：Solution 31P-Nuclear Magnetic Resonance (NMR) is an analysis technology which has been an effective means for the analysis of environmental organic phosphorus. However, the method is rarely applied in the study of wetlands so that the corresponding researches about wetland sediment sample preparation method also very deficient. The present study was aimed to find the most suitable sample preparation method for 31P-NMR analysis of the artificial wetland sediments, using different extractant (NaOH or 0.25 mol·L-1 NaOH+0.05 mol·L-1 EDTA as main extractant, and 1M HCl as pre-extractant or not), sample to extractant ratio (1∶8 or 1∶10), centrifugation conditions and scans time and so on. The results showed that the best 31P-NMR spectrum could be obtained with freeze-ried, ground and sieved sediments, 1M HCl as pre-extractant for 16 h, NaOH+0.05 mol·L-1 EDTA as main extractant for 16 h, extraction ratio of 1∶8, and low temperature and high-speed centrifugation (4 ℃, 10 000 r·min-1 for 30min) for avoiding hydrolysis of certain components. Besides, choosing much longer NMR scan time, as 14～16 h (scans about 25 000 times), could get more complete spectral signals spectrum. And finally, four kinds of P-compounds (orthophosphate, orthophosphate monoesters, orthophosphate diesters and pyrophosphate) were detected in the NMR spectrum. But neither polyphosphate nor phosphonates was not found in all these experiments, which need further study. Compared with the traditional chemical analysis method, 31P-NMR method of sample preparation is relatively simple. Then it is less destructive with components distinguished completely. Using 31P-NMR technology, the cognition of wetland phosphorus cycle, especially organophosphate, will be expected to get new breakthrough.
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