Improving Accuracy and Confidence of Chemical Identification by Gas Chromatography/Vacuum Ultraviolet Spectroscopy-Mass Spectrometry: Parallel Gas Chromatography, Vacuum Ultraviolet, and Mass Spectrometry Library Searches

Abstract

Chemical identification often relies on matching measured chemical properties and/or spectral "fingerprints" of unknowns against their precompiled libraries. Chromatography, absorption spectroscopy, and mass spectrometry are all among analytical approaches that provide chemical measurement databases amenable to library searching. Occasionally, using conventional single-library or single-domain searches can lead to misidentification of unknowns. To improve chemical identification, we present a tandem gas chromatography/vacuum ultraviolet-mass spectrometry (GC/VUV-MS) chemical identification approach that utilizes databases from GC, VUV spectroscopy, and mass spectrometry analyses for a "multidomain" library search. Using standard chemical mixtures as well as aroma compounds as test cases, we demonstrate that multidatabase library searches utilizing GC, VUV, and MS data results in fully correct identification of chemical mixtures examined here that could only be identified with a 69.2% or an 88.5% success rate with MS or VUV library searches alone, respectively. Additionally, we introduce a library- and data domain-independent metric for evaluating the confidence of library search results. Using multidomain library searches improves both the chemical assignment accuracy and confidence.

Comprehensive Two-Dimensional Gas Chromatography Hyphenated with a Vacuum Ultraviolet Spectrometer To Analyze Diesel—A Three-Dimensional Separation (GC × GC × VUV) Approach

“…The spectrum range of VGA-101 spanned from 125 to 430 nm, providing a concentration-sensitive universal response to most molecules. All organic compounds, including all hydrocarbons, have a response in these wavelengths as well as selective diagnostic absorption features. − The VGA-101 has the needed sensitivity and dynamic range to allow for both identification and quantifiable measurement. VUV offers different types of separation and identification than MS; , consequently, it may provide a means of distinguishing coeluting components in a comprehensive two-dimensional gas chromatographic separation that are not resolved by molecular weight or ion fragmentation.…”

GC × VUV Study of Diesel: A Two-Dimensional Separation Approach

“…Gas chromatography with ultraviolet detection (GC–UV) started in the early 1960s. , Continued research from 1980 to 2010 − led to commercial development of the VUV Analytics VGA-101 GC detector capable of providing full spectra from 125 to 430 nm . This VUV detector is concentration sensitive and is considered to be universal, as all organic compounds absorb at these short wavelengths, or selective for specific moieties with diagnostic absorption features. − GC-VUV is complementary to GC-MS, , as both provide insight into the composition of complex mixtures where the GC separation is incomplete and coeluting compounds may be distinguished by their mass or VUV spectra. In theory, all unresolved components could be deconvoluted as each organic compound yields a unique VUV absorption spectrum.…”

Simulation of Vacuum Ultraviolet Absorption Spectra: Paraffin, Isoparaffin, Olefin, Naphthene, and Aromatic Hydrocarbon Class Compounds

“…The complementarity of VUV–UV absorption spectroscopy to mass spectrometry has been demonstrated in numerous studies, including those that combine both VUV and MS analysis for more complete coverage and confidence in assigning identities to components in complex mixtures. 26,27 Whereas FT-ICR-MS can be hardly matched in terms of its ability to speciate the most complex petroleum mixtures, including crude oil, gas chromatography–VUV (GC-VUV) has become an established method for routine day-to-day fuels classification; two ASTM methods are now established using GC-VUV methodology for gasoline and jet fuel analysis, respectively. 28,29 Efforts are still needed to advance GC-VUV methodology for analysis of higher fuels, and the incorporation of theoretical computations is expected to be of benefit for this development.…”