Development and validation of a pneumatic model for the reversed-flow differential flow modulator for comprehensive two-dimensional gas chromatography

The development of the reversed fill/flush modulator represents a significant advancement in flow-modulated, comprehensive two-dimensional gas chromatography (GC × GC). Compared to the forward flush/fill modulator, the reversed-flow modulator is less susceptible to baseline anomalies and peak tailing as a result of modulator channel overfilling or insufficient purging of high concentration analytes. Flow reversal requires the addition of a bleed capillary not present in the forward-flow modulator. Selecting the appropriate restriction of the bleed capillary is critical. If the bleed capillary is too restrictive, eluate from the first-dimension column can split between the modulator channel and second-dimension column, which also results in baseline artifacts. To gain a better understanding of the reversed-flow modulator, a comprehensive pneumatic model was developed. The model was validated by comparing calculated and measured hold-up times. The errors in calculated hold-up times were less than 1% of the measured values. The model can be used to predict first-dimension eluate splitting and determine the optimal bleed capillary dimensions to prevent its occurrence. Calculation of the modulator hold-up time can be used to determine the maximum collection time to ensure comprehensive analysis and optimal flush times for partial fill operation.