Thermodynamic-based retention time predictions of endogenous steroids in comprehensive two-dimensional gas chromatography

This work evaluates the application of a thermodynamic model to comprehensive two-dimensional gas chromatography (GC x GC) coupled with time-of-flight mass spectrometry for anabolic agent investigation. Doping control deals with hundreds of drugs that are prohibited in sports. Drug discovery in biological matrices is a challenging task that requires powerful tools when one is faced with the rapidly changing designer drug landscape. In this work, a thermodynamic model developed for the prediction of both primary and secondary retention times in GC x GC has been applied to trimethylsilylated hydroxyl (O-TMS)- and methoxime-trimethylsilylated carbonyl (MO-TMS)-derivatized endogenous steroids. This model was previously demonstrated on a pneumatically modulated GC x GC system, and is applied for the first time to a thermally modulated GC x GC system. Preliminary one-dimensional experiments allowed the calculation of thermodynamic parameters (Delta H, Delta S, and Delta C (p) ) which were successfully applied for the prediction of the analytes' interactions with the stationary phases of both the first-dimension column and the second-dimension column. The model was able to predict both first-dimension and second-dimension retention times with high accuracy compared with the GC x GC experimental measurements. Maximum differences of -8.22 s in the first dimension and 0.4 s in the second dimension were encountered for the O-TMS derivatives of 11 beta-hydroxyandrosterone and 11-ketoetiocholanolone, respectively. For the MO-TMS derivatives, the largest discrepancies were from testosterone (9.65 s) for the first-dimension retention times and 11-keto-etiocholanolone (0.4 s) for the second-dimension retention times.