Optimizing the optical configuration for light-pipe gas chromatography/Fourier transform infrared spectrometry interfaces

Previous investigators have predicted that by optimizing the optical configuration of the light-pipe interface between a gas chromatograph and a Fourier transform infrared spectrometer and utilizing detectors with areas as small as 0.01 mm/sup 2/, detection limits might be reduced to the subnanogram level. The results presented in this report indicate that this is presently not possible and suggest that the detection limits at ambient temperatures of a practical light-pipe interface can be improved by no more than 50% compared to contemporary systems. Three optical configurations are evaluated for their ability to discriminate against emission from the end of a hot light-pipe. Of these, the most effective in reducing the signal loss normally encountered at elevated light-pipe temperatures utilizes an aperture at a focus between the light-pipe and detector. A loss in signal of only 20% is observed when the temperature of the light-pipe is raised from ambient to 300/sup 0/C by using this optical configuration.