Considerations on Orthogonality Duality in Comprehensive Two-Dimensional Gas Chromatography

Abstract

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.

Improved Separation of Complex Polycyclic Aromatic Hydrocarbon Mixtures Using Novel Column Combinations in GC × GC/ToF-MS

“…To date, a common column combination used for environmental sample analysis in GC×GC/ToF-MS includes a non-polar GC-column in the first dimension followed by a more polar column in the second dimension 11, 14, 16,23,24,25 . In a previous study, this column combination resulted in good chromatographic separation and good space occupation for GC×GC/ToF-MS analysis of a coal liquefaction middle distillate sample containing semi-volatile organic compounds (SOCs) with different physicochemical properties, such as paraffins (alkanes), naphthenes (cyclic alkenes), aromatics and phenols.…”

A New Dimension in Separation Science: Comprehensive Two‐Dimensional Gas Chromatography

“…[26] A separation-space evaluation method based on Denaulays triangulation algorithms was proposed by Semard et al, [27] and then further used to optimize the selection of column sets, geometric parameters of the secondary column, Even though non-polar polar column combinations are often stated as the preferred approach for GC GC, nonclassical conditions, that is, polar moderately non-polar column combinations [28] as well as liquid crystalline, [29] ionic liquid, [30] and enantioselective stationary phases, [31][32][33][34] are gaining attention and can lead to high-resolution and grouptype separations. Moreover, Omais and co-workers [35] recently suggested that the non-polar polar column combination is not a necessary condition to achieve large peak distribution in the 2D plane, and non-classical conditions can occasionally provide a large occupation of 2D space. Thus, there are no fixed rules for the combination of column-phase types.…”

Die umfassende zweidimensionale Gaschromatographie – eine neue Dimension für analytische Trennwissenschaften

“…Omais und Mitarbeiter [35] schlugen kürzlich vor, dass die unpolare polare Kombination stationärer Phasen keineswegs eine zwingende Voraussetzung für eine breite Signalverteilung im zweidimensionalen Trennraum ist. Nichtklassische Kombinationen kçnnen den Trennraum gelegentlich besser mit Signalen komplettieren.…”