Quantitative performance of the reverse fill/flush flow modulation in the conditions when the second gas chromatography column outlet pressure is not equal to the atmospheric pressure

Reverse fill/flush flow modulation is an effective approach for peak modulation in comprehensive two-dimensional chromatography, and several home-made or commercial solutions are currently available to users. In terms of configuration, systems with either a fixed bleed capillary or tuneable 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 are not possible when the secondary gas chromatography column outlet pressure is not equal to the outlet pressure of the bleed capillary (atmospheric pressure). When the secondary column outlet is connected to a detector such as for example Vacuum ultraviolet detector or to a purged splitter where an elevated constant pressure is applied in order to maintain a constant split between two detectors, which were both tested in this study, in these cases the temperature change during the GC run imposes 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 seems not to be not very important when a fixed bleed capillary is used but can be very important if a tuneable auxiliary flow of carrier gas is rather employed. Additionally, it was demonstrated through theoretical calculations and experiments that the dependence of the auxiliary carrier gas flow necessary for maintaining a certain constant modulation channel flow from temperature is not linear but rather 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 ...