Infrared (ir) spectral measurement of gas chromatographic (GC) peaks has been discussed many times in the literature; the combination can provide a convenient means for specific analyses of complex mixtures, provided sufficient sensitivity can be achieved with the infrared device. Sensitivity considerations have until recently limited the utility of a GC/ir combined system, since only GC peaks with microgram quantities or higher could be studied with the infrared technique. Azarraga was the first to substantially demonstrate infrared sensitivities in the submicrogram range, on studies at the 200 to 500 ng level in GC peaks of a variety of molecular systems. Current efforts in coupling ir to GC have taken two distinctly different directions. On the one hand, the infrared lightpipes are optimized to standard existing GC conditions which require ultimately high ir sensitivity because of the small GC peak volumes. The other approach which has been very successfully pursued by Hirschfeld and collaborators involves designing a completely different GC to match predetermined ir optimized conditions. With this approach sensitivity in the nanogram range is no longer the primary objective since the new GC techniques allow much larger injection volumes.

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