The characteristics of the FT-IR spectra of selected types of organic compounds in five different phases, vapor phase (VP), solid state/condensed phase (SS), matrix isolation with Xe (MIXe), matrix isolation with Ar (MIAr), and on a bare disk at 10K (DISK) are presented. Unexpectedly, in the majority of instances, the major absorption bands for compounds trapped in the Xe matrix (MIXe) were found at lower energies than the same compounds trapped in an Ar matrix (MIAr). Surprisingly, the MIXe C-H streches/bend values for linear alkanes were found to be lower than those found in the solid state (SS). This was the first example of this type of behavior. It was documented that noble gases were not insert hosts in terms of absorption values for numerous types of organic compounds. The shifts induced by each host were consistent and questions as to the “inertness” of the hosts were raised. When spectra were gathered on a bare gold disk (DISK) at 10K the absorption bands were, for the majority of cases, found at lower values than the comparable MIXe and MIAr phases. Narrow full width at half height values for most absorptions, at acceptable matrix gas to analyte ratios, were found to be around 5-10 cm^-1. Aggregation was postulated as being the controlling factor in band broadening. Multiple absorptions for compounds with only one functional group, for example a sole carbonyl group, were observed and attributed to the presence of discrete conformers isolated in the matrix gas. Applications of gas Chromatography/matrix isolation/Fourier transform-infrared spectrometry (GC/MI/FT-IR) to the analysis of complex mixtures and trace level environmental samples were discussed. Advantages in the determination of geometrical isomers at very low levels were documented.