Courtesy of the Perkin Elmer Corporation
Figure 40. Stack Plot of Spectra from Gasoline Analysis
The spectra were continuously stored as they were scanned, and as a consequence, any particular spectrum could be easily recovered and used for either direct solute identification, or in the case of an completely unknown solute, could be use to help in structure elucidation. As well as being able to present the individual spectra as selected, they could also be presented in the form of a stack plot as shown in figure 40. The stacked plot shown depicts each spectrum, as it was taken, throughout the elution of each peak. It is clear that the combination of the two techniques, using a suitable interface (e.g., a light pipe) can provide extremely useful data for a wide variety of sample types.
Courtesy of the Perkin Elmer Corporation
Figure 40. Stack Plot of Spectra from Gasoline Analysis
The application of the GC/FTIR system to determine the individual aromatic hydrocarbons in gasoline was reported by Diehl et al (13). By using selected wavelengths at which specific hydrocarbon types exhibited maximum adsorptivity, the maximum sensitivity could be achieved for each aromatic or group of aromatic hydrocarbons. Diehl et al. used a Hewlett-Packard Model 5890 Series II GC/5965 IRD FTIR, with an open tubular column 60 m long and 0.53 mm I.D., carrying a 5.0 mm film of stationary phase on the internal surface. The column was programmed from 40ûC to 190 ûC at 2ûC per min. and then to 300ûC at 30ûC per min. The light pipe and the transfer line were held at 300ûC. By using appropriate wavelengths, the elution of the aromatic hydrocarbons could be exclusively monitored. The chromatograms obtained are shown in figure 41. The separation was fairly lengthy, extending well over an hour but this investment in time was repaid in selectivity. The aromatic hydrocarbons are exclusively monitored, and the numerous aliphatic and unsaturated hydrocarbons, (also present in the mixture) gave little or no response at the selected wavelength.
