Performance of the Reverse Fill/Flush Flow Modulation With Tunable Auxiliary Forward-Pressure Control in the Conditions When the Second Gas Chromatography Column Outlet Pressure Is Different From the Atmospheric Pressure

Reverse fill/flush flow modulation is an effective approach for peak modulation in comprehensive two-dimensional gas chromatography, and several homemade or commercial solutions have been demonstrated. In terms of configuration, systems with either a fixed bleed capillary or tunable forward or back pressure regulation permit to effectively maintain an optimal modulator channel flow and good modulation performance. In both cases, however, in the up-to-date reported works, the modulator channel flow regulation conditions remain constant during the GC run. In this work it was shown that if the objective is to maintain a constant modulator channel flow, constant pressure–resistance regulation conditions can be an issue when the secondary gas chromatography column outlet pressure is not equal to the outlet pressure of the bleed capillary. When the secondary column outlet is connected to a detector, such as, for example, VUV, or to a purged splitter where an elevated constant pressure is applied, which were both tested in this study, in these cases the temperature changes during the GC run impose having to vary the chosen pressure resistance conditions for maintaining a constant modulator channel flow. It was shown, however, that modulator channel flow variation during the GC run appeared minimal when a fixed bleed capillary was used but increased significantly if a tunable auxiliary flow of carrier gas was rather employed. In addition, it was demonstrated through theoretical calculations and experiments that the temperature dependence of the auxiliary carrier gas flow necessary for maintaining a certain constant modulator channel flow is not linear but rather closer to a second-degree polynomial. While a linear approximation can be sufficient in some cases, in other cases the modulation performance can be impacted more significantly, and thus auxiliary carrier gas flow programming according to a second-degree polynomial model can be preferred.