Resolving complex mixtures by means of pulsed gradient spin-echo NMR experiments
Resolving complex mixtures by means of pulsed gradient spin-echo NMR experiments
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DOI：
10.1039/b110472a
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发表时间：
2002-01-01
影响因子：
3.3
通讯作者：
Palazzo, G
中科院分区：
文献类型：
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作者：
Ambrosone, L;Ceglie, A;Palazzo, G
我们提出了一种分析具有相同核磁共振共振的化合物混合物(例如聚合物溶液或脂肪族化合物混合物)的脉冲梯度自旋回波(PGSE)数据的方法。如果所有自旋物种都经历布朗运动，它们对实验回波衰减的贡献是指数的(即e(-SD)，S是PGSE-核磁共振实验参数的函数，D是自扩散系数的函数)。对于在给定化学位移下有多个扩散组分的情况，(归一化)回波衰减是自扩散系数分布函数的拉普拉斯变换。拉普拉斯变换可归结为变量z与e(-Sd)成正比(在区间[0，1]内)的第一类Fredholm型积分方程。应用我们(L.Ambrosone，A Ceglie，G.Colafemmina和G.Palazzo，J.Chem)先前开发的算法。太棒了。1999、110、797)求解积分方程组，得到扩散系数的分布函数。该方法是为典型的PGSE-核磁共振测量的小数据集(10-30点)量身定做的。此外，相关变量(Z)是自扩散系数的指数函数，它允许洞察扩散谱的Ne结构。该方法在三组分溶液和七种聚乙二醇齐聚体的水溶液上成功地进行了测试。在后一种情况下，得到了分子质量分布函数的估计。报道的结果表明，这种方法可以以高精度(6-3%)测定误差15%的自扩散系数。
We present a method to analyse pulsed gradient spin-echo (PGSE) NMR data from a mixture of compounds sharing the same NMR resonance (e.g. polymer solutions or mixtures of aliphatic compounds). If all the spin-bearing species undergo Brownian motion, their contribution to the experimental echo decay is exponential (i.e. e(-sD), with s a function of the parameters of the PGSE-NMR experiment and D the self-diffusion coefficient). For the case of more than one diffusing species at a given chemical shift, the (normalized) echo attenuation is the Laplace transform of the distribution function of the self-diffusion coefficients. The Laplace transform can be reduced to a Fredholm integral equation of the first kind in the variable z proportional to e(-sD) (in the interval [0,1]). Applying the algorithm previously developed by us (L. Ambrosone, A Ceglie, G. Colafemmina and G. Palazzo, J. Chem. Phys. 1999, 110, 797) we solve the integral equation, obtaining the distribution function of the diffusion coefficients. The method is tailored for small data sets (10-30 points) typical of PGSE-NMR measurements. Moreover, the relevant variable (z) being an exponential function of the self-diffusion coefficient, it allows insight on the ne structure of the diffusion spectrum. The method was successfully tested on a three-component solution and on an aqueous solution of seven PEG oligomers. In the latter case an estimate of the molecular mass distribution function was obtained. The reported results indicate that such an approach permits determination of self-diffusion coefficients differing by 15% with a high accuracy (6-3%).