Optimization of extraction and parameters for ³¹P-NMR analysis of organic phosphorus extracted from aquatic plants and algae

Characterization of organic phosphorus (P_o) from aquatic plants and algae by solution ³¹P-Nuclear Magnetic Resonance (³¹P-NMR) is important to understand its biogeochemical cycling in lakes. Methods of extraction and selection of parameters for NMR characterization and quantification of Po critical. Various extractants and radio of sample to extractants were applied for 31P-NMR. A mixture of 0.5 mol/L NaOH-25 m mol/L EDTA with a ratio of sample to extractant of 1: 60 was the optimal extraction of Po from aquatic plants and algae. When the extract was analyzed by use of 31P-NMR, the delay time (D1) and scanning time were set to 5 s and 15 h, respectively, which resulted in approximately 24, 000 scans. Based on how Samples were extracted and results of 31P-NMR analysis, P in aquatic plants and algae included orthophosphates, orthophosphate monoesters, orthophosphate diesters and pyrophosphate, of which Po accounted for 34%~53% and 31%~73% respectively. Orthophosphate monoester was the predominant constituent of Po, which accounted for 92 and 83% of plants and algae, respectively. The proportion of orthophosphate diesters was small in aquatic plants and algae and accounted for only 0~6.65% of the TP. The content of pyrophosphate in algae was approximately 35-fold greater than that in aquatic plants.