Temperature-dependent self-diffusion coefficients of water and six selected molecular liquids for calibration in accurate 1H NMR PFG measurements
Temperature-dependent self-diffusion coefficients of water and six selected molecular liquids for calibration in accurate 1H NMR PFG measurements
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DOI：
10.1039/b005319h
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发表时间：
2000-01-01
影响因子：
3.3
通讯作者：
Sacco, A
中科院分区：
文献类型：
--
作者：
Holz, M;Heil, SR;Sacco, A
脉冲磁场梯度（PFG）核磁共振如今是一种测定自扩散系数D的常规方法。然而，一个仍待实现的目标是提高该方法的精度。通过PFG核磁共振测定准确扩散系数的最佳步骤是用一个D值精确已知的样品进行校准。在我们之前于25℃进行校准的工作（M. 霍尔茨和H. 魏因加特纳，《磁共振杂志》，1991年，92卷，115页）的基础上，我们给出了作为温度函数的参考数据。由于水作为液体和一级标准起着突出的作用，我们通过氢 - 1脉冲磁场梯度核磁共振仔细测量了在 +5℃到 +55℃温度范围内水的自扩散系数，并补充了在0℃到 +100℃范围内通过示踪法获得的文献数据。这个相对大量的数据集合随后可以拟合到一个斯皮迪 - 安杰尔幂律，这表明了两种完全不同方法的结果具有极好的一致性，并证明了水的绝对值的确定性。通过这种方式，获得了误差限<1%的可靠的一级标准值，使我们能够使标准水的温度适应所关注的样品温度。我们还给出了在 +5℃到 +55℃范围内六种容易获取的溶剂的氢 - 1脉冲磁场梯度核磁共振自扩散参考数据，我们提议将它们作为二级校准标准，即环己烷、二氧六环、十二烷、二甲基亚砜、十四烷和戊醇，它们涵盖了很大范围的绝对D值，并使我们能够另外使校准样品和被研究样品的绝对D值相匹配。此外，所获得的准确的自扩散数据适合用于对分子液体物理学中的理论方法进行精细检验。
Pulsed magnetic field gradient (PFG) NMR is today a routine method for the determination of self-diffusion coefficients, D. However, a remaining goal is the improvement of the precision of the method. The best procedure for the determination of accurate diffusion coefficients by PFG NMR is a calibration with a sample of precisely known D-value. In continuation of our previous work on calibration at 25 degrees C (M. Holz and H. Weingartner, J. Magn. Reson., 1991, 92, 115) we present reference data as a function of temperature. Since H2O plays an outstanding role as liquid and as primary standard, we carefully measured self-diffusion coefficients of water by H-1 PFG NMR in the temperature range from +5 to +55 degrees C and added literature data obtained from tracer methods in the range between 0 and +100 degrees C. This comparatively large collection of data could then be fitted to a Speedy-Angell power law, showing the excellent congruence of the results of two completely different methods and proofing the certainty of the absolute values for water. In this manner reliable primary standard values with error limits of < 1% were obtained, allowing us to adapt the temperature of the standard water to the sample temperature of interest. We further give H-1 PFG NMR self-diffusion reference data in the range from +5 to +55 degrees C for six easily accessible solvents, which we propose as secondary calibration standards, namely cyclohexane, dioxane, dodecane, DMSO, tetradecane and pentanol, covering a large range of absolute D-values and allowing us to match in addition the absolute D-values of calibration sample and sample under investigation. Furthermore, the gained accurate self-diffusion data are suited for an elaborate check of theoretical approaches in the physics of molecular liquids.