Measurements and Correlation for Diffusion Coefficients for Large Molecules in Non-organic Solvents

虽然泰勒分散法已被广泛用于测量有机化合物在各种溶剂如超临界流体和水溶液中的扩散系数，但由于严重的拖尾，它不适合于极性化合物。本文提出了一种用聚合物涂层毛细管柱测定极性溶质的色谱脉冲响应（CIR）方法。本研究的目的是测量和关联各种大分子和/或极性化合物在超临界二氧化碳中的扩散系数，为了将CIR方法应用于高分子量化合物的测量，提出了两种技术改进方法：二次流效应的校正和对极低吸收强度响应曲线的噪声消除技术。根据螺旋毛细管柱CIR法的二阶中心矩，推导出了校正二次流效应的换算公式， ...更多信息 高流速。用摄动法得到了它的实用表达式，直到λ^<10>，其中λ是管半径与线圈半径之比。在没有校正的情况下，DeSc^&lt;1/2&gt; &lt; 8-9.5的有效范围扩大到DeSc^&lt;1/2&gt; &lt; 18-19，以确定扩散系数，误差在1%以内。曲线拟合法经去噪处理后，可准确测定D_<12>（1/2）值，且在最低吸收强度处有效，即10 ~（？）<-4>吸光度单位数量级，对应于最小量的溶质。使用CIR方法与噪声消除技术和二次流效应的校正，各种化合物，如酸，酯，甘油酯，和醇在超临界二氧化碳中的扩散系数进行了测量。结果表明，D<12>/T与溶剂粘度的关系式和施密特数关系式对预测效果较好。少

Although the Taylor dispersion method has been widely employed to measure diffusion coefficients of organic compounds in various solvents such as supercritical fluids and aqueous solutions, it is not suitable for polar compounds due to severe tailing. We have developed the chromatographic impulse response (CIR) method with a polymer coated capillary column for measurements for polar solutes. The objective of this project is to measure and correlate diffusion coefficients of various large molecular and/or polar compounds under supercritical carbon dioxide.To apply the CIR method to measurements for higher molecular weight compounds, two technical improvement methods have been developed : correction of the secondary flow effect and noise elimination technique for response curves having extremely low absorbance intensity. A conversion formula to correct for the secondary flow effect was derived from the second central moment of the CIR method with a coiled capillary column at relatively h … More igh flow rates. Its practical expression was obtained analytically by the perturbation method up to λ^<10>, where λ is the ratio of the tube radius to the coil radius. The effective range of DeSc^<1/2> < 8-9.5 without correction widened to DeSc^<1/2> < 18-19 to determine the diffusion coefficient within 1% error. The curve-fitting method with the noise elimination treatment was quite effective for determining the D_<12> values accurately, and was valid at the lowest absorbance intensities, on the order of 10^<-4> absorbance unit of UV-Vis multi-detector, corresponding to the smallest quantity of the solute. Using the CIR method with the noise elimination technique and the correction of the secondary flow effect, diffusion coefficients of various compounds such as acids, esters, glycerides, and alcohols were measured in supercritical carbon dioxide. Two predictive correlations, equation of D_<12>/T with solvent viscosity, and the Schmidt number correlation, were found effective for the prediction. Less