A Practical Approach for Validation of Compound Identification in Comprehensive Two-Dimensional Gas Chromatography-Mass Spectrometry.

A simple curve-fitting approach for the retention index (I) calculation without reference compound injection was established. This was applied to validate compound identification data in comprehensive two-dimensional gas chromatography coupled with mass spectrometry (GC × GC-MS). Different models were investigated for calculating I in the first (1D) and second (2D) dimensional separations (1ICal and 2ICal, respectively) with the input data of compound names, elution temperature (Te), and experimental retention time (tR,Exp) of peaks, taking into account the wraparound effect. By comparing ICal and the literature I (ILit) of 495 compounds, a more suitable model was the exponential equation containing eight coefficients, which showed average R2 of 0.9982 and 0.9957, mean absolute error (MAE) of 8.29 and 12.89, and root mean squared error (RMSE) of 11.63 and 16.48 for 1I and 2I comparisons, respectively. For compound validation, the initial assumption was that most of the peaks in a data set were identified with the correct compound names. The least-squares curve fitting was then performed to match 1ICal and 2ICal with 1ILit and 2ILit of these compounds. The compounds could be validated with correct identities when the fitting shows 1I and 2I differences (Δ1I = 1ILit - 1ICal and Δ2I = 2ILit - 2ICal, respectively) within ±60 units. Compounds showing |Δ1I| or |Δ2I| outside this range (observed with the coordinates out of the linear trendline of the ICal vs ILit plot) were suspected with incorrect identities. The developed approach was applied to validate 1741 peaks of 15 samples analyzed in this study. By using tentative identification based on "only MS" and "MS and 1I" identification criteria, 536 (out of 995) and 534 (out of 746) compounds, respectively, were suspected to have incorrect identities. Example reannotation of 61 peaks with more correct identities was also demonstrated. In addition, the approach was used to screen 1285 (out of 7445) suspected compounds in 85 GC × GC-MS results reported from the literature.