Design and implementation of comprehensive gas chromatography with cryogenic modulation

Comprehensive gas chromatography is the realization of true continuous mult idimensional (dual column) gas chromatography, The key requirement in the c omprehensive GC experiment is that the second dimension analysis is complet ed in a rapid time-frame compared to the elution of components in the first dimension, and that the two coupled dimensions represent 'orthogonal' anal yses towards the analytes to be separated. The former normally necessitates pulsing of contiguous segments of each chromatographic band from the first to the second dimensions. The two dimensions should be in fluid communicat ion. The comprehensive GC x GC experiment passes all the column flow from t he first column to the second column, leading to no sample loss, but this a lso requires a suitable method for time- or zone-compression of the band to be pulsed to the second column. The final purse should be narrow, and shou ld be delivered to the second column quickly. A simple procedure can achiev e this using the cryogenic modulator that has been recently described by th is group. The system uses a cryogenic trap which can be moved away from the cooled zone of the column faster than 10 ms. A fast-acting pneumatic ram a chieves this performance. The cooled column heats up to the prevailing oven temperature within 10-15 ms. Molecules as volatile as C5 alkanes or small aromatics will be fully retained by the trap within the period of modulatio n used for GC x GC, The technique is simple to implement and requires no sp ecial column connections. Using a gas chromatograph which allows control of external events and can acquire from a detector at 50 Hz or faster, and a timing controller for modulation, the comprehensive result can easily and e ffectively be achieved.