New operational modes for multidimensional and comprehensive gas chromatography by using cryogenic modulation

Historically, hardware and method-related concerns have limited the use of multidimensional gas chromatography in the routine laboratory. This paper presents a new approach that offers the potential to significantly alter the manner in which multidimensional gas chromatography is conducted, based on the use of a modulated cryogenic trap which can be moved longitudinally along the column. Two columns are directly coupled, and no switching valves are used. It is demonstrated that a heartcut section can be cryofocused and zone-compressed, and then rapidly remobilized at the prevailing column oven temperature without any supplementary heating. A short second dimension column is used, giving fast second dimension analysis. This allows a large number of heartcuts to be programmed for any one analysis. The ‘ultimate’ manifestation of multidimensional gas chromatography is the comprehensive GC technique (GC×GC). This is now simply effected by performing very rapid heartcuts at intervals on the order of 1/5th of the peak width of primary dimension peaks, and requires that the second dimension be able to complete the analysis of each collected zone on a similar timeframe. This paper uses a semi-volatile aromatic mixture to demonstrate these selected operational modes, that can be achieved with the longitudinal modulation method. The flexibility that arises from this approach is shown by the ability to swap between selected whole-peak enhancement and comprehensive modes during the one analytical run. The increased sensitivity that follows from peak compression is a further advantage, which would be beneficial for trace analysis.