Two-dimensional gas chromatography (2DGC) has emerged as a powerful tool in separating complex volatile mixtures. System resolution and sensitivity are limited by the thermal modulator injection plug width. The injection plug width from a modulator that is uniformly heated and cooled is limited by the heating rate, the cooling rate and the carrier gas velocity. A resistively heated thermal modulator has been developed that produces injection plug widths significantly narrower than are capable with a uniform modulator. It consists of a 10 cm piece of deactivated stainless steel tubing interiorly coated with a stationary phase. For modulator evaluation, a steady-state concentration of organic vapor is fed to the modulator. After a suitable sample collection period, the first stage, comprising the upstream 2/3 of the modulator, is heated rapidly, allowing the sample to desorb and quickly flow downstream. The sample is decelerated when it encounters the second stage, focusing the band. Upon firing of the second stage, the narrow band flows directly to the detector. A closed loop refrigeration system has also been developed which uses no consumables. The purpose of a modulator cooling system is to prevent breakthrough for the full length of the second column separation. As a cooling system’s ability to cool increases, the required length of modulator decreases, decreasing injection plug width for a given carrier gas velocity. Injection peaks utilizing both the two-stage modulator and the liquid cooling system have been characterized and will be compared to with those from other 2DGC systems operated under similar conditions. Two-dimensional chromatograms will illustrate the impact of injection plug width on separation quality.
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