Comprehensive Gas Chromatography−Time-of-Flight Mass Spectrometry Using Soft and Selective Photoionization Techniques

Abstract

The hyphenation of gas chromatography and mass spectrometry (GC/MS) revolutionized organic analysis. In GC/MS coupling, usually electron impact ionization is applied, and molecules are identified by their fragment pattern. Although mass spectrometry in principle is a separation method, it is used predominantly as a spectrometric technique. However, if soft (i.e., fragmentation-free) ionization techniques are applied, the inherent separation character of MS is emphasized, which has similarities to a GC boiling point separation. By combining polar column GC separation and fast soft ionization time-of-flight mass spectrometry technology, a comprehensive separation of complex petrochemical samples can be obtained (GC x MS approach). Compounds of comparable physical-chemical properties are characteristically grouped together in a two-dimensional retention time-m/z representation. This resembles the separation characteristics of comprehensive two-dimensional gas chromatography (GC x GC) and, thus, represents a novel multidimensional separation approach. In this work, a gas chromatograph equipped with a polar separation column was coupled to a home-built laser ionization time-of-flight mass spectrometer. Laser-based, single-photon ionization was used for universal soft ionization and resonance-enhanced multiphoton ionization for selective ionization of aromatic compounds. A novel capillary-jet inlet system was used for the coupling. Multidimensional comprehensive analysis of complex petrochemical hydrocarbon samples using gas chromatography coupled to mass spectrometry with soft and selective photo ionization sources is first demonstrated.

Comprehensive two‐dimensional gas chromatography‐mass spectrometry: A review

“…The main difference between the two methods consists in the fact that in GC-MS, a single compound can produce several m/z signals, whereas only a single retention time signal is produced in GC Â GC (Phillips & Xu, 1995). Several years later, a simulated GC Â MS chromatogram was compared to that of a hydrocarbon GC Â GC chromatogram (Schoenmakers et al, 2000), whereas very recently, GC Â time-of-flight (ToF) MS diesel chromatograms have been generated by using soft ionization methodologies (Wang, Qian, & Green, 2005;Mitschke, Welthagen, & Zimmermann, 2006).…”

“…Comprehensive gas chromatography coupled to soft ionization mass spectrometry (GC Â MS) representation, using SPI-mass spectrometry. A: With the GC Â MS chromatogram before transformation and (B) the chromatogram after doing the ''Kovats Index''-like transformation of the retention time axes (Mitschke, Welthagen, & Zimmermann, 2006; reproduced with written permission from the American Chemical Society).…”

“…The similarity increases between the two methodologies if soft ionization techniques are employed; the lack of fragmentation and the formation of the sole molecular ions highlights the second-dimension separation capabilities of mass spectrometry. In 2006, conventional gas chromatography combined with soft photoionization (SPI) ToF-MS was employed to generate GC  MS fuel chromatograms, which were completely similar to their GC  GC-FID counterparts (Mitschke, Welthagen, & Zimmermann, 2006). Although the method is not quite within the marked boundaries of the present review, a brief description will be provided: a 30 m  0.25 mm ID moderately polar column was used to introduce analyte bands to a laboratory-constructed laserionization ToF-MS.…”

Multidimensional and Comprehensive Two-Dimensional Gas Chromatography

“…However, if unknowns are the main issue-as in, e.g., many air analyses and metabolomics, and in quite a number of organohalogen and essential oil studies-automated detection and data presentation still are complex and time-consuming operations. In-depth discussions, and partial solutions, of these problems can be found in several papers published by Zimmermann and his group [54,60,61].…”

An ultracompact photo-ionization time-of-flight mass spectrometer with a novel vacuum ultraviolet light source for on-line detection of organic trace compounds and as a detector for gas chromatography

“…In previous experiments, a gas chromatograph equipped with a polar separation column was coupled to a homebuilt time-of-fl ight laser photo-ionization mass spectrometer. 28 Laser-based single-photon ionization (SPI) was used for universal soft ionization, and resonanceenhanced multiphoton ionization (REMPI) was used for selective ionization of aromatic compounds. A novel jet inlet was used for the coupling.…”