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the solute automatically regenerated into an IR cell, where the spectrum was taken and a separate
sample passed to the mass spectrometer. The cell used for IR measurement was one of the early
examples of the light pipe. The light pipe is a tube that has the internal walls made reflective, by coating
with gold or some other appropriate material. Light pipe interfaces are the most commonly used
interfaces for GC/IR today, and a number of different manufacturers produce efficient light pipe
systems. The conduit to the light pipe, and the light pipe itself, must be maintained at a temperature that
will prevent any solutes condensing on the surface. In general, the interface conduit and light pipe,
should be maintained at least 20°C above the maximum temperature attained by the chromatography
column. The light pipe interface has been successfully used for many commercial applications
including pharmaceutical products, essential oils, and petroleum products. The cryostat interface, also
popular, but considerably more expensive, consists of a drum cooled with liquid helium, on the surface
of which the column eluent condenses. A mixture of argon and helium is often used as the mobile phase
and so the sample is trapped in a solid argon matrix, which eliminates the possibility of catalytic
decomposition or molecular rearrangement on the metal surface. The drum rotates, and a physical
chromatogram is formed as a spiral of solutes, condensed on the drum surface. Reflective IR spectra
are taken from the drum surface. The cryostat interface, which is by far the most sensitive GC/IR
interface, has also been used with thermogravimetric instruments forming the TGA/GC/IR triplet
system.

References

1. R. P. W. Scott, I. A. Fowliss, D. Welti and T. Wilkens, Gas Chromatography 1966, A. B. Littlrwood
(Ed.) The Institute of Petroleum, London (1966)318.

2. R. P. W. Scott, in Gas Chromatography 1964, A. B. Littlewood(Ed.) The Institute of Petroleum,
London (1966)25.

3. P. A. Wilks and R. A. Brown, Anal. Chem.36((1964)1896.

4. J. W, Diehl, J. W. Flinkbeiner and F. P. DiSanzo, Anal. Chem. 67(13)(1995)2015.

5. A. B. Attygalle, A. Svatos and C. Wilcox, Anal. Chem. 66(10)(1995)1696,

6. N. Ragunathan, A. T. Sasaki, K. A. Krock and C. L. Wilkins, Anal. Chem., 66(21)( 1995)3751.