dc.description.abstract | This study consists of two objectives: one is to develop a GC x GC method with electron capture detection ( ECD ) to analyze trace levels ( ~pptv ) of atmospheric halocarbons, the other is to analyze complex liquid samples by GC x GC with flame ionization detection ( FID ).
To analyze atmospheric halocarbons a self-built pre-concentrator was employed for in-line enrichment before analyzed by GC x GC – ECD. To further lower the detection limits of chlorofluorocarbon ( CFC ) replacements, oxygen doping technique was adopted for electron capture detection. The GC x GC used a valve type modulator based on the Deans switch method. Analytes after eluting from the first column were cut into slices and sent to the second column for two-dimensional separation. A commercially available software, SuferR 8, was used to process the data into three-dimensional concentration contour plots. The column combination of DB-5 x TG-1301 was found to show the best separation results for halocarbons. The correlation coefficients ( R2 ) of 2D vs. 1D results were greater than 0.9920. The reproducibility ( RSD based on N = 30 ) was better than 0.94% for all target halocarbons. The method can be used in either online or offline mode. Flask samples can be analyzed when the system is operated in off-line mode, whereas continuous monitoring is possible when the system is operated in on-line mode.
As the second objective to analyze complex liquid samples, such as perfume, essential oil, wine, gasoline and biofuel, etc. the Deans switch GC x GC – FID method was tested. The column combination of DB-5 x DB-1 was found to show the optimal separation results. Rather than pursuing full separation as with the halocarbon analysis, the concept of “pattern recognition” of complex samples was adopted. A product series with minor composition variation can be distinguished based on pattern difference. This application is found particular useful where imitating products can be easily separated apart from their genuine counterparts. When compare the self-made GC x GC – FID method with the commercial GC x GC / ToF-MS method using the identical column combination, compound identification becomes possible, which further broadens the applicability of the proposed method.
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