The GCxGC Technique

In order to manipulate the selectivity of the FT synthesis, there needs to be an understanding of the parameters that control the selectivity. The preceding discussion gives a flavor of what Sasol is doing regarding the understanding of Fe-LTFT selectivities. There are many activities to ensure more accurate measurements, e.g., developments in the GCxGC technique. There are also attempts... 

The modulator is the heart of the GCxGC system, and is positioned at the confluence of the coupled chromatography columns. The role of the modulator is to trap or isolate compounds present in a given time fraction eluting from the first-dimension column and reinject these components rapidly into the second column. This essentially yields a time-sampled chromatogram, from the first dimension ( D) to the second dimension ( D). It is critical that the modulator is capable of representatively and faithfully sampling peaks eluting from onto D. This can be achieved by either complete or partial transfer of the first-column eluent, however, both techniques are considered comprehensive. 

GC xGC can be used for basic research purposes, but the theoretical considerations presented here are related mainly to its practical aspects. As for other chromatographic techniques, the GCxGC main objective is the qualitative and quantitative analysis of complex mixtures. Chapters in the second part of this volume detail its analytical applications in several fields, usually including its use as a quantitative tool. 

As illustrated above, GCxGCxGC is currently not yet practical. LCxGCxGC appears to be more feasible. In the development of a system for the latter technique, the question of how to interface the various dimensions holds a key position. To answer this question, it is wise to first look in more detail at how subsequent dimensions in a comprehensive system can be interfaced. In GCxGC, just as in LC xLC , the D analyses are usually performed on-the-fly. That is, the separation on the first column continues while the previous time fraction is analysed on the second column. Two other operational approaches... 

Fig. 3. GCxGC-TOF-MS total ion current (TIC) plot of Rosa damascena Mill. volatilelS components at 150°C using the DTD technique (Ozel et al., 2006).

In the present chapter we want to demonstrate in the form of chemo-ecological/analytical study the applicability of the GCxGC-TOFMS for achiral and chiral insect semiochemicals analysis together with another key instrumental technique in this research - the gas chromatography with electroantennographic detection (GC-EAD). The insects we described in the study were the two above mentioned Chinese bark beetle species - Ips nitidus and Ips shangrila. 

Two-dimensional chromatography or GC-GC uses a two-column system as does GCxGC. The two-column configuration is often a source of confusion about the two techniques for non-specialists. 

Another approach in GC is that of using more power in the separation by doing GCxGC. In this approach, a second column is used with a different type of stationary phase than the primary stationary phase, and fast chromatography using TOF-MS as the detector is carried out [39]. This technique uses only TOF-MS as the detector since it has the most sensitivity for fast-eluting peaks. The method has been applied to complicated matrix analysis. 

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