Exchange interference for a range of partially deuterated hydrocarbons using a GC-EI-MSD

Industrial catalyst processes, such as the Fischer-Tropsch (FT) process, produce a vast array of products from syngas (H₂ /CO), such as jet fuel, gasoline, diesel, synthetic rubbers, monomers for plastics industries, and other oil/wax materials for specific purposes such as cosmetics. Multitudes of publications since the discovery of the FT process in 1925 have been composed, attempting to elucidate the mechanism. Many of these publications attempt to investigate the mechanism of FT by the utilization of specific deuterium experimentation through the switching of the syngas from H₂ /CO to D₂ /CO. Results from this switching indicated that hydrogen was involved in the rate-limited step; the overall process conversion produced an inverse kinetic isotope effect. To confirm that results were not hindered by the physical switch of the hydrogen isotopes, further experimentation was performed using equal molar of each isotope competitively (equal molar H₂ /D₂ )/CO. Complications arose from this competitive work as it generated fully exchanged products, i.e. all partially deuterated hydrocarbons that could not be separated by chromatography. These compounds could no longer be separated by the chromatography and required a further separation by mass. The overall scope for this work was to determine if a range of partially deuterated paraffin compounds, generated by FT, can be analyzed using an EI-MSD without interinstrumental H/D exchange. Results indicate that no real exchange occurs in the EI MSD for a carbon range from about C₆ to C₁₆ . Even though the materials cannot be separated chromatographically, they can be further separated and analyzed to determine the overall H/D content for these specific chain lengths.