Generalization of Reference System for Calculating the Second Dimension Retention Index in GC × GC–MS
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Using C4–C25 fatty acid methyl esters (C4–C25 FAMEs) as a sample reference series, a method was developed to generalize the reference system for calculating the second dimension retention index (2I) of compounds analyzed by comprehensive two-dimensional gas chromatography–mass spectrometry (GC × GC–MS). The second dimension elution temperature (2Te), second dimension unadjusted retention time (2tR), and the linear retention index (IT) of C4–C25 FAMEs were used to form a second dimension retention index surface (2IS) via a three-dimensional surface fitting model. The 2I of an analyte analyzed by GC × GC–MS was then calculated from the 2IS based on its 2tR and 2Te. The developed method was validated by calculating the 2I of n-alkanes, 80 compounds, and two commercially available mixtures (MegaMix A and MegaMix B). Compared to the conventional method, the developed method keeps the 2I in n-alkane retention index scale, and enables using any compounds as references to obtain a much increased separation space in the second dimension GC.
KeywordsRetention index Second dimension retention index GC–MS GC × GC–MS
The authors would like to thank Mrs. Marion McClain for review of this manuscript. This work was supported by NIH grant nos. 1P20GM113226 (CJM), 1P50AA024337 (CJM), 1U01AA021893-01 (CJM), 1U01AA021901-01 (CJM), 1U01AA022489-01A1 (CJM), and 1R01AA023681-01 (CJM). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. This work was also supported by the Department of Veterans Affairs 1I01BX002996-01A2 (CJM).
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