Page 178 - Tandem Techniques

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Figure 4.26
Co-added Spectra from Oxidation
Products Sampled Between 290°C and 310°C
Courtesy of the Perkin Elmer Corporation

Integrated IR spectra of the eluent portions collected in the Tenax trap produced the upper
chromatogram shown in Figure 4.27. The lower chromatogram is an expanded portion of the total
separation from 14 to about 30 minutes. The oxidation products of greatest concentration are carbon
dioxide, water vapor, hexanal, heptanal, benzaldehyde, some unresolved acids and aldehydes and some
acid lactones. It is seen that tandem systems employing the light pipe interface for the FTIR
spectrometer are very effective but significantly lower in sensitivity than the cryostatic system.

Without doubt, the most effective GC/FTIR tandem system employs the cryostatic interface and
provides a sensitivity at least one if not two orders of magnitude greater than the contemporary light
pipe interface. It is however, a mechanically complicated device and extremely expensive, relative to
the light pipe alternative. So much so in fact, that the cryostat has been withdrawn from the market and
at this time is no longer commercially available. This is most unfortunate and leaves the analyst with
the light pipe as the only commercial alternative. Nevertheless, there is a need for a high-sensitivity
interface, and this need will continue to grow as the demands of the environmental, forensic and
biological sciences become greater. Hopefully, this increasing demand will evoke the