For the successful crude oil analysis using mass spectrometry, it is critical to select suitable ionization techniques depending on the purpose of the experiment and the sample properties. Paper spray ionization (PSI) is fast and convenient ionization method for the direct analysis of complex mixtures with minimum sample preparation. In addition, ionization and subsequent MS analysis can be done with small amounts of sample. It also has an increased tolerance to high salt contamination. But the application of the PSI is limited to polar compound detection like ESI.
Recently developed paper spray chemical ionization (PSCI) can analyze nonpolar or less polar compounds like APPI or APCI. It also shares the benefits of the use of PSI. When only low volumes and small amounts of samples are available, PSI and PSCI must be beneficial in terms of sample consumption. In this study, paper spray ionization mass spectrometry (PSI) and paper spray chemical ionization (PSCI) were applied to study photo-oxidized and spilled oils.