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.
V. F. Kalasinsky, K. G. Whitehead, R. C. Kenton, and K. S. Kalasinsky, "Double Lightpipe System for Analytical GC/FT-IR and Spectral Libraries," Appl. Spectrosc. 42, 56-60 (1988)