Solution 31P nuclear magnetic resonance (NMR) spectroscopy has been widely applied to analyze the speciation of soil organic P; however, this time-consuming technique suffers from a low analytical efficiency, because of the lack of fundamental information such as the spin–lattice relaxation (T1) of 31P nucleus for model P compounds. In this study, we for the first time determined the T1 values of twelve typical soil organic P compounds using the inversion recovery method. Furthermore, we examined the effect of co-existing paramagnetic ions (e.g., Fe3+ and Mn2+) on the reduction of the T1 values of these compounds. Without the addition of paramagnetic ions, the T1 values of twelve model P compounds ranged from 0.61 s for phytic acid to 9.65 s for orthophosphate. In contrast, the presence of paramagnetic ion significantly shortened the T1 values of orthophosphate, pyrophosphate, and phytic acid to 1.29, 1.26, and 0.07 s, respectively, except that of deoxyribonucleic acid (DNA) remaining unchanged. Additionally, we evaluated the feasibility of improving the efficiency of quantitative 31P NMR analysis via addition of paramagnetic ion. Results show that, after an addition of 50 mg L−1 paramagnetic ions, 31P NMR measurement can be 3 times more efficient, attributed to the reduced T1 and the corresponding recycle delay.

中文翻译：

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土壤有机磷定量溶液的³¹ P NMR分析的改进：对顺磁性离子的自旋-晶格弛豫的研究

溶液31P核磁共振（NMR）光谱已被广泛用于分析土壤有机磷的形态。然而，由于缺乏基本信息，例如模型P化合物的31P核的自旋-晶格弛豫（T1），这种耗时的技术分析效率较低。在这项研究中，我们首次使用反演恢复方法确定了十二种典型的土壤有机磷化合物的T1值。此外，我们研究了共存顺磁性离子（例如Fe3 +和Mn2 +）对这些化合物T1值降低的影响。在不添加顺磁性离子的情况下，十二种P型化合物的T1值范围从植酸的0.61秒到正磷酸盐的9.65秒。相反，除脱氧核糖核酸（DNA）保持不变外，顺磁性离子的存在将正磷酸，焦磷酸和植酸的T1值分别分别缩短至1.29、1.26和0.07 s。此外，我们评估了通过添加顺磁性离子提高31P NMR定量分析效率的可行性。结果表明，在添加50 mg L-1顺磁性离子后，归因于T1的降低和相应的回收延迟，31P NMR测量的效率可以提高3倍。