text: Gas phase species absorb and display unique spectra between 120 – 240 nm where high energy σ→σ*, n→σ*, π→π*, n → π* electronic transitions can be excited and probed. VUV spectra reflect the absorbance cross section of compounds and are specific to their electronic structure and functional group arrangement. The ability of VUV detectors to produce spectra for most compounds results in universal and highly selective compound identification. VUV spectroscopy data is highly characteristic while also providing quantitative information. Many commonly used GC detectors such as the electron capture detector (ECD), flame ionization detector (FID), and thermal conductivity detector (TCD) produce quantitative but not qualitative detail. Gas chromatography–mass spectrometry (GC-MS) generates qualitative and quantitative data but has difficulty characterizing labile and low mass compounds, as well as differentiating between isomers. GC-VUV complements MS by overcoming its limitations and providing a secondary method of confirmation. It also offers a single instrument alternative to the use of multiple detectors for qualitative and quantitative analysis.
  Naphthols, xylenes, and cis- and trans- fatty acids are compounds that are prohibitively difficult to distinguish according to their electron ionization mass spectral profiles. Xylenes present the additional challenge of natural co-elution that makes separating their isoforms problematic. Figure 2 shows the distinct VUV spectra of m-, p-, and o-xylene. These compounds can be differentiated despite their only difference being the position of two methyl groups around a benzene ring. The spectral differences of these isomers enable their co-elution to be resolved through spectral deconvolution.
  Fatty acid screening and profiling is an application that commonly requires the use of multiple detectors to achieve quantitative and qualitative results. FID is a quantitative detector that is suitable for routine screening when guided by retention index information.  GC-MS has traditionally been used for qualitative compound profiling, but falls short where isobaric analytes are prevalent.  It especially struggles with differentiating cis and trans fatty acid isomers. Electron impact ionization can also cause double bond migration and lead to ambiguous fatty acid structural data.
  Determining cis and trans fatty acid distribution in oils and fats is important in assessing their potential health impacts. VUV spectra of trans-containing fatty acid methyl ester (FAME) isomers typically found in butter and vegetable oils are shown in Figure 3. These trans-containing isomers separate chromatographically from cis-containing isomers and have the tendency to co-elute with each other and, in some cases, with select C20:1 isomers. GC-VUV is not only able to differentiate the C18:3 FAME variants, but is also capable of telling cis isomers apart from trans isomers. Degrees of unsaturation such as C20:1 vs. C18:3 can additionally be distinguished. Previous work has demonstrated how distinct VUV spectra enable straightforward deconvolution and accurate quantitation of cis and trans FAME isomers.