LAUSR

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.