Generalization of Reference System for Calculating the Second Dimension Retention Index in GC × GC–MS

Using C 4 –C 25 fatty acid methyl esters (C 4 –C 25 FAMEs) as a sample reference series, a method was developed to generalize the reference system for calculating the second dimension retention index ( 2 I ) of compounds analyzed by comprehensive two-dimensional gas chromatography–mass spectrometry (GC × GC–MS). The second dimension elution temperature ( 2 T e ), second dimension unadjusted retention time ( 2 t R ), and the linear retention index ( I T ) of C4–C25 FAMEs were used to form a second dimension retention index surface ( 2 I S ) via a three-dimensional surface fitting model. The 2 I of an analyte analyzed by GC × GC–MS was then calculated from the 2 I S based on its 2 t R and 2 T e . The developed method was validated by calculating the 2 I 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 2 I 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.