Spray Injection Direct Analysis in Real Time (DART) Ionization for Petroleum Analysis

Limin Ren, Yehua Han^*, Yahe Zhang, Yanfen Zhang, Xianghai Meng, and Quan Shi^*

State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Beijing 102249, People’s Republic of China

Corresponding Authors: ^*E-mail: hanyehua@cup.edu.cn. ^*E-mail: sq@cup.edu.cn.

DOI: 10.1021/acs.energyfuels.6b00018

Keywords: Fossil fuels; Ionization; Ions; Petrochemicals; Sulfides

Abstract: Negative- and positive-ion direct analysis in real time (DART) ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was applied to characterize crude oil and its fractions. Crude oil samples dissolved in toluene were directly infused into a spray needle, which produced a continuous and long-time stable ion current for FT-ICR MS analysis to obtain mass spectra with a broad dynamic range and high signal-to-noise ratio. A comparison between negative-ion electrospray ionization [ESI(−)] and negative-ion DART for crude oil analysis was presented. The DART(−) ionized almost all of the compound classes found in ESI(−), while it exhibited high selectivity on naphthenic acids, which enabled the characterization of naphthenic acids in petroleum with a low total acid number (TAN). The method is suitable for the analysis of naphthenic acids in petroleum distillation cuts, even with a very high boiling point. Sulfides in petroleum were likely oxidized to sulfoxides and exhibited high selectivity in positive-ion DART, indicating that it can potentially be used for the molecular characterization of sulfides in petroleum.