A novel resistively heated and air-cooled thermal modulator for comprehensive two-dimensional gas chromatography (2DGC) has been constructed. The modulator is based on a single-stage air-cooled, wall coated metal capillary tube that is rapidly heated for thermal desorption. Heating is accomplished by sending a current pulse through the metal modulator. The 2DGC system consists of an HP 5890 GC containing a split/split-less injector, a non-polar primary column, a non-polar thermal modulator, a polar second column and a flame ionization detector. The analytical columns are mounted inside a commercial retrofit (RVM Scientific) that allows independent temperature programming of each column relative to the thermal modulator. A novel feature of the system is its ability for very fast temperature programming of the second column for each modulated cycle. A Matlab program has been written to allow for data analysis of the modulated one-dimensional chromatograms. The resulting files can be viewed in three dimensions via GRAMS Spectral Notebook and later converted to a contour plot for graphical presentation. Qualitative information is based upon the reproducibility of component groups along the contour plot for known component samples. Quantitative information is derived from the volume of the three-dimensional peaks by way of Matlab. The 2DGC system was used to analyze a complex petroleum sample. A selection of volatile and semi-volatile components were used as targeted components for qualitative and quantitative analysis. The efficiency of the modulator as a function of cooling flow rate, cooling air temperature, heating time and modulator cycle frequency has been studied. In addition, spreadsheet modeling of the linear velocity, volumetric flow rates, and hold up times for the primary column, thermal modulator and secondary column have been used to optimize the 2DGC system. The results obtained with this 2DGC system are compared with a commercially available 2DGC system.
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