Wick Collin D, Siepman J Ilja, Klotz Wendy L, Schure Mark R
Department of Chemistry, University of Minnesota, Minneapolis 55455, USA.
J Chromatogr A. 2002 Apr 19;954(1-2):181-90. doi: 10.1016/s0021-9673(02)00171-1.
Experiments and molecular simulations were carried out to study temperature effects (in the range of 323 to 383 K) on the absolute and relative retention of n-hexane, n-heptane, n-octane, benzene, toluene and the three xylene isomers in gas-liquid chromatography. Helium and squalane were used as the carrier gas and retentive phase, respectively. Both the experiments and the simulations show a markedly different temperature dependence of the retention for the n-alkanes compared to the arenes. For example, over the 60 K temperature range studied, the Kovats retention index of benzene is found to increase by about 16 or 18+/-10 retention index units determined from the experiments or simulations, respectively. For toluene and the xylenes, the experimentally measured increases are similar in magnitude and range from 14 to 17 retention index units for m-xylene to o-xylene. The molecular simulation data provide an independent method of obtaining the transfer enthalpies and entropies. The change in retention indices is shown to be the result of the larger entropic penalty and the larger heat capacity for the transfer of the alkane molecules.
开展了实验和分子模拟，以研究温度影响（在323至383K范围内）对正己烷、正庚烷、正辛烷、苯、甲苯以及三种二甲苯异构体在气液色谱中的绝对保留和相对保留的作用。分别使用氦气和角鲨烷作为载气和固定相。实验和模拟均表明，与芳烃相比，正构烷烃的保留对温度的依赖性明显不同。例如，在所研究的60K温度范围内，发现苯的科瓦茨保留指数分别通过实验或模拟确定增加约16或18±10个保留指数单位。对于甲苯和二甲苯，实验测量的增加幅度相似，间二甲苯至邻二甲苯的增加范围为14至17个保留指数单位。分子模拟数据提供了一种获取转移焓和熵变的独立方法。保留指数的变化表明是烷烃分子转移时更大的熵罚和更大的热容导致的结果。
