| dc.description.abstract | Comprehensive GCxGC is a chromatographic technique using two different interactions of columns to separate complex compounds in a orthogonal manner. The key component of a comprehensive 2D-GC (GCxGC) system lies in the
modulator installed in between the 1-D and 2-D column. Elution segments from the first column are concentrated and injected in series into the second column for orthogonal analysis. Although thermal/cryogenic designations is the most common modulator type in the recent development, it consumes cryogens such as liquid nitrogen (LN2) or liquid carbon dioxide and is costly as a result. In this study, rather than using a thermal/cryogenic modulator, a Deans’ switch-based modulator was used, which was coupled to a homemade thermal desorption unit for analyzing ambient volatile organic compounds (VOCs). The Deans’ switch
device generated eluent slices from the first column into the second column. One of the novel features with this method is that rather than using common interaction forces of volatility x polarity for GCxGC, this study used volatility x retention. The first-dimension separation was performed by the difference in volatility (boiling point), the second-dimension separation was performed by the difference in retention force between the analytes and the Al2O3 solid phase on the PLOT column. Instead of using the specialized GCxGC software package, a widely available graphic software (Surfer 8) was adopted for plotting results of GCxGC. This data process method allowed peaks to be easily transformed into contour or 3-D surfaces at a minimal cost.
Wrap-around is a common phenomenon seen in GCxGC. It often occurs when peak retention times in the second column are longer than the modulation period, creating ghost peaks on the final contour plot. By simply adjusting modulation periods, wrap-around can be easily detected and then removed. In this study, alkenes over C6 and alkanes over C7 are usually the wrap-around species due to strong retention on the PLOT. Finally, 26 VOC species from C3 to C7, including the co-elution compounds - 2,3-dimethylbutane and
2-methylpentane, were identified by the GCxGC method. The peaks on the contour map could divide into alkane group and alkene group. A calibration curve with sample volumes ranging from 80 to 400 mL was made with an R2 of 0.997 (N=3). The correlation between modulated (GCxGC) and non-modulated (GC) are 0.996.
In summary, by combining off-the-shelf components, an automated valve-based comprehensive GCxGC system was constructed with the advantages of rigidity, simplicity, flexibility, and low cost.
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