Compositional analysis of complex organic mixtures by electrospray ionization Fourier transform ion cyclotron resonance mass spectroscopy.

摘要

Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) has ultrahigh mass resolving power (m/Deltam50% > 300,000) and high mass accuracy (1 ppm), which enables separation and identification of elemental compositions of complicated mixtures. Electrospray ionization (ESI) provides selective ionization of polar heteroatomic compounds without isolation from the complex mixtures. In addition, the Kendrick mass scale (where CH2 is 14.00000 rather than 14.01565) is introduced in petrochemical analysis for an easy and fast data reduction.; Petrochemicals like coal and crude oil are among the most chemically complex natural mixtures in the world. Heteroatomic compounds contribute to the instability in storage and environmental contamination by releasing relevant acid precursor gases such as SOx and NOx upon combustion. To meet stringent environmental regulations and to produce a quality product, it is necessary to remove those heteroatoms through clean fuel technology. Thus it is essential to monitor the fates of the heteroatom-containing compounds through those processes. We first apply ESI FT-ICR mass spectrometry to the analysis of Illinois #6 and Pocahontas #3 pyridine coal extracts. With the aid of Kendrick mass scaling, the elemental compositions can be sorted into homologous series according to compound "class" and "type". Both the compositional and aromaticity data correlate well with known compositional and geochemical information. Furthermore, the same technique is extended into study of coal liquefaction and coal fractionation. In the coal liquefaction study, a distillation resid and a further processed liquid product were examined by ESI FT-ICR MS. The resid sample contains more heteroatomic compounds whereas the liquid sample is lower in average mass and also much more saturated. The coal fractionation technique facilitates sorting of coal components by comparing a standard pyridine extract with two alternative fractions designed to concentrate acidic components: coal acids and acidic asphaltenes. The resulting detailed compositional analysis of coal acids provides detailed distributions of heteroatomic classes, aromaticity, and alkylation of coal. That kind of information establishes a fundamental basis for assessing the role of those acids in coal processing. Moreover, we utilized two- and three-dimensional van Krevelen diagrams that allow visual resolution of complex mixtures. The van Krevelen plot not only graphically exaggerates the difference between different classes, but more importantly affords a simple graphical basis for exposing compositional differences between samples of different nature, origin, and processing.; We also extended this work to other complex mixtures, such as hydrotreated fuels, military explosives and vegetable oils. In the study of fuel hydrotreatment, detailed elemental composition comparisons of different hydrotreating conditions provide a new and rational basis for optimizing parameters for hydrotreatment of commercial oils. And in explosive analysis, we are able to identify both active and non-active components in post-blast explosive residues. Thus it provides the forensic basis to trace the origin of an explosive. In vegetable oil analysis, we resolve and identify literally thousands of distinct chemical components of commercial canola, olive and soybean oils, without extraction or other wet chemical separation pretreatment. We suggest that adulteration of vegetable oils can be detected by detailed elemental compositional fingerprints.