Facile Approach for Calculation of Second Dimensional Retention Indices in Comprehensive Two Dimensional Gas Chromatography with Single Injection.

In the present work, a novel and simple approach to generate isovolatility curves for alkane series was established, which serves to calculate the second dimension (2D) retention indices (2 I) for peaks in comprehensive two-dimensional gas chromatography (GC×GC). The approach is applicable to routine GC×GC results without requiring multiple injections of alkanes or requiring internal and external standards under different oven temperature conditions which might be normally required in other approaches. A proposed relationship between 2 I values and first dimension (1D) and 2D retention times (1 tR and 2 tR) of compounds can be simplified to an equation with four constants. Values of the four constants can be obtained by fitting the proposed equation with experimental 1 tR and 2 tR data of standard compounds obtained from a single injection of a standard mixture or by using data of known compounds in an analyzed sample. The effect of selected compound sets on calculation of the four constants and derivation of 2 I using the established approach was investigated. The approach was evaluated by comparison with the traditional method based on multiple injections in calculating 2 I values of compounds in a frankincense sample. With a suitable set of chosen standard compounds well-spread over the first and second dimension (2D) space, the potential of the present concept allows simple and reliable calculation of 2 I. This approach should facilitate application of 2 I for compound identification in GC×GC, which is somewhat underutilized largely due to the tedious and time-consuming approach presently used in construction of isovolatility curves, based on multiple injections.