|High-resolution MS coupled to Photoionization-GCxGC for Petrochemicals Characterization
|Multidimensional and Comprehensive Separation Science
|Dr Anupam Giri
|Mr Omid Emamjomeh
Abstract Information :
Structural elucidation of hydrocarbon classes, heteronates impurities and functional biomarkers in petroleum products are always in high demand. Sheer number of compounds in petrochemicals sample quickly exceeds the available peak capacity of single-column GC techniques. Consequently the use of multidimensional separation techniques is almost invariably required. Despite the superior separation afforded by GCxGC, the identification of individual compounds in complex petrochemicals remains challenging where majority of compounds in a hydrocarbon class displays similar skeleton-spectra at conventional (70 eV) ionization energies.
In this study, application of photoionization (PI) coupled with GCxGC-HRTOF-MS was evaluated. This soft-ionization technology was shown to enhance analyte speciation by providing superior data on both molecular ions and structurally significant fragments in low-energy (10.8 eV) PI mass spectra. The enhanced sensitivity and selectivity stemming from the dramatic reduction in fragmentation at low energies also greatly increases the number of compounds identified, permitting robust statistical comparisons essential for successful chemical fingerprinting of petrochemicals. In addition, applicability and added benefits of hybrid and simultaneous EI and PI for different hydrocarbon classes were evaluated and will be discussed.
Chromatographic resolution achieved by GCxGC can further be enhanced by coupling high resolution (HR) MS. HRMS has the ability to resolve very narrow mass differences between isobars; e.g., C3 vs SH4 (0.0034 Da), CH2 vs N (0.0126 Da), and CH4 vs O (0.0364 Da). GCxGC-PI-HRMS with prominent molecular ions can add several other dimensions on top of two dimensional chromatographic separation. Depending on the resolving power of the MS, added dimensions could be-
1). near unambiguous mass determination,
2). detection of heteroatom classes,
3). degree of unsaturation,
4). carbon number characterization,
and 5). elemental compositions and could be used for improved visualization and characterization of petrochemicals.