page_title: Gas chromatography–vacuum ultraviolet spectroscopy
section_title: Compound class characterization
hierarchical_section_title: Gas chromatography–vacuum ultraviolet spectroscopy / How it works / Compound class characterization
caption_attribution_description: English: Zoomed-in chromatogram of gasoline sample with key PIONA compound class representative peaks labeled. Inset figure shows analyte spectral features fit with VUV library olefin compound class spectral response information. The residual fit statistical data indicating a good fit is also shown.
context_page_description: Gas chromatography–vacuum ultraviolet spectroscopy is a universal detection platform for gas chromatography. VUV detection provides both qualitative and quantitative spectral information for most gas phase compounds.
  GC-VUV spectral data is three-dimensional and specific to chemical structure. Nearly all compounds absorb in the VUV region of the electromagnetic spectrum with the exception of carrier gases hydrogen, helium, and argon. The high energy, short wavelength VUV photons probe electronic transitions in almost all chemical bonds including ground state to excited state. The result is spectral "fingerprints" that are specific to individual compound structure and can be readily identified by the VUV library.
  Unique VUV spectra enable closely related compounds such as structural isomers to be clearly differentiated. VUV detectors complement mass spectrometry, which struggles with characterizing constitutional isomers and compounds with low mass quantitation ions. VUV spectra can also be used to deconvolve analyte co-elution, resulting in an accurate quantitative representation of individual analyte contribution to the original response.
context_section_description: GC-VUV can be used for bulk compositional analysis because compounds share spectral shape characteristics within a class. Proprietary software applies fitting procedures to quickly determine the relative contribution of each compound category present in a sample. Retention index information is used to limit the amount of VUV library searching and fitting performed for each analyte, enabling the automated data processing routine to be completed quickly. Compound class or specific compound concentrations can be reported as either mass or volume percent. 
  GC-VUV bulk compound characterization was first applied to the analysis of paraffin, isoparaffin, olefin, naphthene, and aromatic (PIONA) hydrocarbons in gasoline streams. It is suitable for use with finished gasoline, reformate, reformer feed, FCC, light naphtha, and heavy naphtha samples. A typical chromatographic analysis is displayed in Figure 7. The inset shows how the analyte spectral response is fit with VUV library spectra for the selected time slice. A report detailing the carbon number breakdown within each PIONA compound class, as well as the relative mass or volume percent of classes, is shown. A table with mass % and carbon number data from a gasoline sample can be seen in Figure 8. Compound class characterization utilizes a method known as time interval deconvolution (TID), which has recently been applied to the analysis of terpenes.
caption: Zoomed-in chromatogram of gasoline sample with key PIONA compound class representative peaks labeled. Inset figure shows analyte spectral features fit with VUV library olefin compound class spectral response information. The residual fit statistical data indicating a good fit is also shown.
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