Investigation of different crude oils applying thermal analysis/mass spectrometry with soft photoionisation

A variety of crude oil samples have been investigated by the combined methods of thermal analysis and mass spectrometry by means of a newly developed prototype of a thermogravimetry-single photon ionisation time-of-flight mass spectrometer coupling (TG-SPI-TOFMS). Single photon ionisation (SPI) was conducted utilising a novel electron beam pumped argon excimer lamp (EBEL) as photon source, and a TOFMS with orthogonal acceleration has been applied for the detection of the mass to charge signals. The advantage of the soft SPI technique over EI for the analysis of such complex samples could be clearly demonstrated, as the aliphatic hydrocarbons present in crude oil may be detected via their respective molecular ion signals, not showing the intense fragmentation typical for EI spectra of this substance class. The application of SPI revealed furthermore two distinct decomposition regions, dominated by evaporation and pyrolysis processes, respectively. Moreover, different crude oils could be distinguished by TA/SPI mass spectra due to their unique molecular signatures.