The ultimate in capillary GC/MS coupling

The minimum plate height of high resolution capillary WCOT columns is increased bij 12.5% at most, when the columns outlet pressure is reduces from atmospheric to below 1 kPa*. At the same time, the optimum carrier gas velocity shifts to appreciable higher values, dependent on the outlet pressure. The decreased column efficiency can easily be compensated by using a longer column. The net effect can be more theoretical plates without increased speed of analysis. The advantageous effects described above hold for WCOT columns whereby the resistance towards mass transfer in the liquid phase is negligible compared to that in the gas phase. This is valid for glass capillaries with uniformly distributed thin liquid films, but also for wide-bore columns with thick films. The latter have higher sample capacities, show less adsorption, and facilititate injection. The best GC/MS interface device thus appears to be no divice at all: just insert the column into the ion source of a mass spectrometer. In addition to the gain in speed of analysis and/or GC resolving power, the many problems caused by wall effects in GC/MS interface lines are avoided by this method. Theoretical considerations and practical examples of reduces pressure GC/MS will be presented.