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Figure 3: Zoomed in Total Ion Chromatogram from Figure 2 demonstrating (outlined) the explicit 1D co-elution resolved by the second dimension retention time (y-axis, top image). Further the partial summary table of processed results from the software indicating the Group (matches) and 2-Dimension retention times.
increase the accuracy of identification. This contour plot also shows column bleed peaks (banana shaped yellow-green trails), which are likely amplified due to the solvent used in the mixtures. Regardless of these challenges our results indicated a very high rate of successful identification.
In Figure 3, we examine one of many significant sections of 1st dimension GC co- elution separated by the second dimension of chromatography (y axis), each peak being separated by ≈ 100 msec. This is an interesting example since it shows how detailed the results can be for one area of first dimension co-elution. The table below the contour plot shows the match level assigned (Group), 1st dimension Retention Index (calculated), Mass Accuracy for the Molecular Ion (ppm), Formula, and Similarity score from the NIST library. Note that peaks # 893 and 902 did not have retention index information in the NIST library. Although all the other level A criteria passed it became a sub classification of the A Match. Peak # 898 was also an A level match but the deconvoluted mass spectra did not have a molecular ion, however the Chemical Ionisation spectrum did have that molecular ion evidence at the same retention time. The quality of the mass spectra generated in close second dimension GC proximity (200
msec) are shown in Figure 4 for Peaks 893 and 896. These two examples show greater than 900 similarity scores on comparison of deconvoluted to library spectra.
In Figure 5 for a particular set of ions you can see an increase number of deconvoluted peaks from 3 to 5 (increased peak capacity). Table 3 shows highlights the increased quality of the identifications obtained with comprehensive GCxGC. Undetected peaks in 1D are found in GCxGC with increased similarity scores and mass accuracies staying within the bounds of the forecasted accuracy
(< 5ppm). There is just one example of many cases where this occurred the frequency of this occurrence co-elution in these samples is also the subject of a future publication.
Accuracy of Identification of Standard Sample Mixtures
The final topic for discussion is the overall accuracy of the identification experiment. Figure 6 shows the blind accuracy of about 84% for all samples when comparing to the NIST available compounds. Further
Figure 4: Deconvoluted mass spectra (Peak True) and their corresponding Library spectra for Peaks 893 and 896 in Figure 3.
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