An Overview of Gas Chromatography – Vacuum Ultraviolet Spectroscopy for Petrochemical Analysis

Vacuum ultraviolet absorption spectroscopic detection for gas chromatography (GC-VUV) was introduced in 2014. Since then, it has been established as a complementary tool to traditional gas chromatography - mass spectrometry (GC-MS) for qualitative and quantitative analysis. GC-VUV is based on the absorption detection of volatile and semi-volatile species from 120 - 240 nm, where all chemical compounds absorb and have unique absorption signatures. GC-VUV excels in the differentiation of isomeric species, especially where GC-MS has problems. Further, different compound classes display common absorption features. This leads to unique capabilities for classification and speciation of complex mixtures. To date, GC-VUV has been applied for analysis of a variety of petrochemical-related samples - from finished gasoline to specialty chemicals, such as polychlorinated biphenyl compounds, to weathered diesel. Based on the simple additivity of overlapping absorption events, peak deconvolution is readily accomplished, removing significant burden on chromatographic separations to resolve all components in a mixture. Advanced treatments, such as time interval deconvolution (TID), have been demonstrated for automated speciation and classification of complex mixtures. Notably, TID is the basis of a new ASTM method D8071 for PIONA and oxygenate analysis of finished gasoline. Quantitative analysis is also simplified given that absorption intensity is directly proportional to analyte concentration, per the well-known Beer-Lambert Law. The absorption cross-section (molar absorptivity) is a physical property of a molecule, and this also facilitates means for calibration-less or pseudo-absolute quantification. Finally, absorption processes can be modeled using theoretical methods, a distinct advantage over other GC detection methods, and the use of computations to support petrochemical analysis in this regard is advancing. In this talk, an overview of petrochemical analysis to date using GC-VUV and associated data treatments will be given, touching on many of the aspects mentioned above.