Enhancing ²D retention index accuracy: Correcting ²D retention time shifts in GC×GC due to modulation timing...

Even small deviations in modulation timing (DMT) can cause discrepancies between the originally set modulation period (P_m) and the actual P_m in comprehensive two-dimensional gas chromatography (GC × GC) analysis. This study explored the impact of DMT on the accuracy of the second dimensional retention time (²t_R) and the second dimensional retention index (²I) calculations and introduced a line detection technology (LDT) based on the Hough Transform to correct DMT-induced ²t_R shifts. The correction was achieved by automatically adjusting candidate P_m values until the slope of the line(s) (CB_line(s)) formed by column bleeding compound peaks in the isothermal section of the contour plot approached zero, thereby determining the actual P_m. The effects of DMT magnitude, CB_line length, sampling frequency, and column set type on the method's accuracy were examined. Results indicated the method is applicable to most GC × GC analyses, provided the CB_line length is at least 5 min and the sampling frequency is ≥ 20 Hz. The accuracy and significance of the proposed method were demonstrated through analyses of a Grobmix sample and a Liquiritia sample, respectively. The LDT-based method offers a simple, time-efficient approach to rectify DMT-induced ²t_R shifts in GC × GC. By enhancing ²I calculation accuracy, it improves the reliability of structurally similar compound identification in complex samples, which is significant for qualitative analysis in the GC × GC field.