Facile Approach for Calculation of Second Dimensional Retention Indices in Comprehensive Two Dimensional Gas...

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 t_R and ² t_R) 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 t_R and ² t_R 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.