Selective Characterization of Olefins by Paternò-Büchi Reaction with Ultrahigh Resolution Mass Spectrometry

Petroleum olefins play important roles in various secondary processing procedures and are important feedstocks for the modern organic chemical industry. It is quite challenging to analyze petroleum olefins beyond the gas chromatography (GC)-able range using mass spectrometry (MS) due to the difficulty of soft ionization and the matrix complexity. In this work, a Paternò-Büchi (PB) reaction combined with atmospheric pressure chemical ionization and ultrahigh resolution mass spectrometry (APCI-UHRMS) was developed for selective analysis of olefins. Through the PB reaction, C═C bonds were transformed into four-membered rings of oxetane with improved polarity so that soft ionization of olefins could be achieved. The systematic optimization of PB reaction conditions, as well as MS ionization conditions, ensured a high reaction yield and a satisfied MS response. Furthermore, a sound scheme was set up to discriminate the coexisting unsaturated alkanes in complex petroleum, including linear olefins, nonlinear olefins, cycloalkanes, and aromatics, making use of their different behaviors during the PB reaction and chemical ionization. The developed strategy was successfully applied to the analysis of olefins in fluid catalytic cracking oil slurry, a complex heavy oil sample. This method extended the characterization of petroleum olefins from lower to higher with high efficiency and selectivity to provide a comprehensive molecular library for heavy petroleum samples and process optimization.