不同pH条件下典型有机磷核磁图谱差异性解析

液相磷-31核磁共振波谱技术(31PNMR)是当前国内外土壤有机磷(Po)分子形态表征的主流分析技术,其主要利用乙二胺四乙酸-NaOH溶液提取,然后在高pH值(pH=13)条件下采集谱图.然而,高pH值条件下P.可能水解,同时鉴于实际土壤pH值通常在6～8范围内,因此有必要探究pH值对P.核磁谱图的影响.对D-葡萄糖-...

Investigation on the Spectral Variation of Typical Organic Phosphorus Compounds under Different pH Conditions Using Solution 31P NMR Spectroscopy

Liquid phosphorus-31(³¹P)nuclear magnetic resonance(NMR)spectroscopy is one of the major analytical technique for the characterization of soil organic phosphorus(P_o)species at the molecular level,and usually requires to extract soil P_o using NaOH-EDTA(ethylene diamine tetraacetic acid)solution before the spectrum is collected under high pH(pH=13)conditions.However,soil P_o may be hydrolyzed under high pH conditions,which affects the accuracy of the P-NMR measurements.Furthermore,the pH of soils usually ranges from 6 to 8,and thus it is necessary to explore the differences in the spectra of P_o compounds under different pH conditions.Typical P compounds including D-glucose-6-phosphate disodium(D-G-6-P),5′-adenosine monophosphate(5′AMP)and sodium dihydrogen phosphate standards were selected for this study under different pH conditions.The results show that the pH change significantly affects spectral features of the investigated P_o compounds.For D-G-6-P,the shape and peak positions of the NMR spectra both change under varied pH conditions,but pH mainly affects the position of 5′AMP and NaH₂PO₄ absorption peaks.D-G-6-P hasα-and β-forms in solutions,and transforms into glucose phosphate,mannose phosphate,fructose phosphate and saccharinic acid phosphate,but it mainly exists as 3-hydroxy-2-oxopropyl phosphate and saccharinic acid after degradation,accounting for more than 50% of the total content,at high pH.For 5′-adenosine monophosphate,there are three conformations of 5′AMP in the solution.The resolved peak at high pH probably results from the hydrolysis of 5′AMP to produce orthophosphate,while for NaH₂PO₄,the existence of H₂PO₄^- and HPO₄^2- at low and high pH values leads to changes in the peak shift in the spectra.Overall,the extraction of P_o using NaOH-EDTA solution with high pH may significantly change the speciation of P_o,and thus induce the changes in their spectra.This study provides theoretical bases for the comprehensive understanding of soil P_oNMR spectra and the development of new method to characterize soil P_o speciation at pH values approaching natural soil pH ranges.