CYHPO oxidation followed by methylation for selective characterization of thiophenic and sulfidic compounds in petroleum via ESI FT-ICR MS

Abstract

In the present paper, the molecular composition of sulfidic and thiophenic compounds in petroleum samples were selectively characterized by positive-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) after cyclohexanone peroxide (CYHPO) oxidation followed by methylation. The sulfidic compounds in petroleum were mainly oxidized to sulfones by CYHPO while most of thiophenic compounds were not reacted. In the followed methylation process, the unreacted thiophenic compounds were converted to methylsulfonium. After using ammonium formate (HCOONH4) as a promoter, the obtained sulfidic sulfones (O2S1 class species) were selectively ionized in the form of N1O2S1 class species under positive-ion ESI FT-ICR MS. The thiophenic methylsulfonium salts in the oxidation-methylation products were also identified by positive-ion ESI FT-ICR MS as S1 class species. This analytical scheme was evaluated by a variety of model compounds and then applied successfully to diesel, VGO and crude oil samples to obtain the molecular composition of sulfidic and thiophenic compounds. In addition, the molecular type of biomarkers and other compounds in petroleum samples can be identified by this analytical scheme.