OPTIMIZED SAMPLING IN GAS CHROMATOGRAPHY INFRARED SPECTROSCOPY INTERFACE

The optimum volume for a flow-through gas cell used in the gas chromatography-infrared spectroscopy interface (GC-ir) is shown to be equal to the volume of carrier gas between the half-width points of the GC peak. The optimum length and diameter for light-pipe gas cells for GC fractions separated using 1/8 in. packed columns and support-coated open tubular columns has been calculated for infrared measurements made using a rapid-scanning Fourier transform infrared spectrometer with either a triglycine sulfate or a mercury cadmium telluride detector. A sampling trigger actuated by the inflection points of the GC peak has been shown to be superior to the more usual threshold type of trigger. Expressions for the delay time between actuation of the trigger and initiation of data collection are also derived.