IFP Energies Nouvelles, BP3, 69360 Solaize, France.
Anal Chem. 2011 Oct 1;83(19):7550-4. doi: 10.1021/ac201103e. Epub 2011 Aug 30.
The term "orthogonal" in comprehensive two-dimensional gas chromatography (GC × GC) has a double sided meaning as it stands for a separation resulting from the combination of two independent retention mechanisms (Giddings, J. C. J. High Resolut. Chromatogr. 1987, 10, 319) but also for a 2D separation where the components are evenly distributed over the entire 2D space. It is shown in the present study that a nonorthogonal GC × GC system associating a polar stationary phase in the first dimension (poly(ethylene glycol)) to a nonpolar one in the second dimension (poly(dimethyl siloxane)) leads to a structured chromatogram, a high peak capacity, and a great 2D space occupation. This idea is demonstrated through the characterization of oxygenated compounds in a coal-derived middle distillate. Results show a clear separation between oxygenated species and hydrocarbons which are classified into linear alkanes, cyclic alkanes, and aromatics. A breakthrough configuration combining a polar poly(ethylene glycol) first dimension and a trifluoropropyl methyl stationary phase in the second dimension enabled a unique identification and quantification of linear, cyclic, and aromatic alcohols. This configuration which could be considered as nonorthogonal still involves two different retention mechanisms: polarity and boiling point in the first dimension and electronic interactions in the second dimension. It is selective toward electronegative poles of alcohols and phenols. The contributions of these two configurations compared to a conventional orthogonal system as well as their roles for oxygenated compounds speciation are highlighted. This contribution is measured through three 2D space occupation factors. It appears through these two examples that orthogonality is intimately linked to analyte properties, and a general concept of dimensionality must be considered.
全二维气相色谱（GC×GC）中的“正交”一词具有双重含义，它既代表两种独立的保留机制组合产生的分离（Giddings，J. C. J. High Resolut. Chromatogr. 1987, 10, 319），也代表二维分离，其中各组分均匀分布在整个二维空间中。本研究表明，在非正交 GC×GC 系统中，第一维采用极性固定相（聚乙二醇），第二维采用非极性固定相（聚二甲基硅氧烷），可得到结构型色谱图、高的峰容量和大的二维空间占有率。通过对煤衍生中间馏分中含氧化合物的表征，验证了这一想法。结果表明，含氧物种和烃类之间存在明显的分离，烃类可分为直链烷烃、环烷烃和芳烃。采用极性聚乙二醇第一维和三氟丙基甲基固定相第二维的突破构型，实现了直链、环烷和芳烃醇的独特鉴定和定量。这种构型虽然可以被认为是非正交的，但仍涉及两种不同的保留机制：第一维的极性和沸点以及第二维的电子相互作用。它对醇和酚的电负性基团具有选择性。与传统正交系统相比，这两种构型的贡献以及它们在含氧化合物形态分析中的作用得到了强调。这一贡献通过三个二维空间占有率因子来衡量。通过这两个实例可以看出，正交性与分析物的性质密切相关，必须考虑到维度的一般概念。
