Double Lightpipe System for Analytical GC/FT-IR and Spectral Libraries

A GC/FT-IR accessory has been configured with two lightpipes in order to allow flexibility in chromatographic separations. A capillary column is connected to a 15-cm lightpipe (1.5-mm bore) and is used for analytical GC/FT-IR. The second lightpipe (42-cm, 3-mm bore) is connected to a packed column and is configured with valves to provide a stopped-flow capability. This lightpipe is used when the sample size is not limited or when signal-averaging and high resolution are necessary. Broad-band MCT detectors are generally used because they are not adversely affected by unmodulated blackbody radiation from the heated lightpipe. In those instances when a narrow-band MCT detector is needed, an aperture and one additional mirror are used to discriminate against the unmodulated radiation. Applications of both systems are discussed.