Correlation Studies Between Physical and Chemical Properties of Crude Oil and FT-ICR Mass Spectra

Mass spectrometric analysis of crude oil by Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometry is a well-established method to study these complex mixtures on the molecular level. Single compounds can be detected in crude oils without any purification or separation step due to the ultra-high resolution and extremely high mass accuracy of this technique. Compound classes can be analysed based on the molecular formula - the calculated number of hetero atoms and the double bond equivalents. Correlation studies of crude oils using APPI and statistical approaches have shown good correlation between amount of sulphur in the samples and the detected compound classes containing sulphur like S1, S2 and SO2. 

However, the compounds detected by mass spectrometry are heavily dependent on the ionisation method used, such as APPI, as well as other factors like solvents used for atmospheric pressure ionisation, addition of metals or use of acids or bases to improve ionisation of specific compounds. In a recent study, Bruker analysed the correlation of APPI as well as LDI FT-ICR mass spectra with the chemical and physical properties of crude oils. Using LDI dramatically reduces all the dependence on ionisation conditions and solvents. The results demonstrated the relative abundances of the sulphur compound classes detected by APPI and LDI both increased with amount of sulphur in the sample.