IFP Énergies nouvelles, BP3, 69360 Solaize, France.
J Chromatogr A. 2012 Sep 14;1255:196-201. doi: 10.1016/j.chroma.2012.07.042. Epub 2012 Jul 24.
This paper explains how one single stationary phase can involve two different elution orders for linear alkanes, cyclic alkanes, aromatics and phenols using comprehensive two-dimensional gas chromatography. For this purpose, a coal-derived middle distillate was injected in nonpolar×semipolar and polar×semipolar configurations implying the same second dimension stationary phase (trifluoropropyl). Results show that even if the same column is utilised as a second dimension, the group-type elution order is reversed from one combination to the other. This can be explained as follows:for the polar×semipolar combination, each fraction eluting from the first dimension contains species that differ so much in terms of boiling points, that volatility plays a key role in the second isothermal separation. This is exemplified by the separation of a phenol and demonstrated using the proportional relationship between retention times, vapour pressures and activity coefficients. Moreover, van't Hoff plots (plots of ln k vs. 1/T) demonstrated the influence of the elution temperature from the first dimension on the second dimension separation. Therefore, available choice of stationary phase's combinations is much higher considering that one single column leads to very different retentions for similar compounds. Finally, this can explain why a reverse orthogonality approach is usually proficient for the separation of polar compounds.
本文解释了如何使用全二维气相色谱法，使单一固定相对于正构烷烃、环烷烃、芳烃和酚类化合物呈现出两种不同的洗脱顺序。为此，将一种源自煤的中间馏分分别以非极性-半极性和极性-半极性的方式注入，这两种方式的第二维固定相（三氟丙基）相同。结果表明，即使使用相同的柱作为第二维，组类型洗脱顺序也会从一种组合变为另一种组合。这可以解释如下：对于极性-半极性组合，从第一维洗脱的每个馏分包含沸点差异很大的物质，因此挥发性在第二维等温分离中起着关键作用。这可以通过酚类化合物的分离来证明，并使用保留时间、蒸气压和活度系数之间的比例关系来加以说明。此外，范特霍夫图（ln k 对 1/T 的图）证明了第一维洗脱温度对第二维分离的影响。因此，考虑到单一柱对相似化合物的保留行为差异很大，固定相组合的选择范围要大得多。最后，这可以解释为什么反正交方法通常擅长分离极性化合物。
