Optimization of Atmospheric Pressure Photoionization for the Crude Oil Analysis Using Ultra-High Resolution Mass Spectrometry

Abstract

Design of experiments (DOE) applied to mass spectrometry (MS), mainly focusing on the optimization of ionization techniques, has been applied to optimize experiments in order to provide the highest amount of information with the lowest number of experiments. However, DOE has not been used in petroleomics. For the first time, we applied DOE to optimize the main parameters associated with the crude oil analysis in a petroleomics approach. For the ionization technique, atmospheric pressure photoionization (APPI) has been selected and data were acquired in a high resolution (400,000 at m/z 400) and high mass accuracy (< 1 ppm) Fourier transform ion cyclotron resonance (FT-ICR) MS. Full and fractional two-level factorial designs were applied for the APPI(±) FT-ICR MS data set from two different crude oil samples with distinct physical and chemical characteristics. The standard ionization parameters that affect the MS responses of the crude oil analysis were optimized for both APPI(+)-MS and APPI(-)-MS. Such ionization parameters were then successfully applied to a crude oil and its saturated, aromatics, resin and asphaltene fractions, all with superior features of merit. Thus, the optimized APPI(±)-MS parameters should serve as reference and can be used as a guide for new studies in petroleomics.

Solvent and Flow Rate Effects on the Observed Compositional Profiles and the Relative Intensities of Radical and Protonated Species in Atmospheric Pressure Photoionization Mass Spectrometry

“…Design of experiments (DoE) has previously been used to optimize experimental parameters for ESI 48 and APPI-FTICR MS 49 analysis of petroleum samples, with an flow rate of 3000 μL h −1 that is suggested to be optimal for positive-mode (+) APPI analysis of crude oils. 50 However, the responses considered were factors such as the maximum intensity, total number of ions, or molecular classes generated; the R/P was not reported. In this work, DoE was carried out with R/P as the response factor to improve understanding of the impact of the solvent system, sample concentration, and flow rate on the observed (+) APPI profile.…”

“…Design of experiments (DoE) has previously been used to optimize experimental parameters for ESI and APPI-FTICR MS analysis of petroleum samples, with an flow rate of 3000 μL h –1 that is suggested to be optimal for positive-mode (+) APPI analysis of crude oils . However, the responses considered were factors such as the maximum intensity, total number of ions, or molecular classes generated; the R/P was not reported.…”

A three-dimensional semi-quantitative method to monitor the evolution of polycyclic aromatic hydrocarbons from vacuum gas oil feedstocks to lighter products

“…Since PAHs have an ionisation energy smaller than 10 eV, their direct ionisation can be performed thanks to photons from the krypton lamp [30]. Moreover, several works showed that APPI in positive mode is one the most suitable and efficient atmospheric pressure ionisation source for PAHs ionisation [31][32][33]. The first dimension of the three-dimensional method, CPC, allows a separation according to the alkylation stage of the hydrocarbons whereas the second one, SFC, is based on their double bond equivalent (DBE).…”

Input of an Off-Line, Comprehensive, Three-Dimensional Method (CPC×SFC/HRMS) to Quantify Polycyclic Aromatic Hydrocarbons in Vacuum Gas Oils

“…Many studies dealing with a petroleomic approach have applied Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR/MS), which is one of the most powerful techniques to go deeper into the characterization of heavy oils thanks to its ultrahigh resolution. − Among the available ionization sources, the positive ion mode atmospheric pressure photoionization source [(+)­APPI] seemed to be the most efficient one for HPAH ionization. − Moreover, dopants are usually employed to increase the ionization efficiency, such as toluene, − chlorobenzene, , anisole, or a mix of several compounds. , However, mass spectrometry alone cannot resolve the complexity of petroleum samples mainly due to (1) ionization discrimination and (2) the presence of isomeric species. Subfractionation can be performed prior to mass spectrometry analysis, such as the SARA fractionation method, which separates samples into four major classes of compounds (saturates, aromatics, resins, and asphaltenes), mainly on the basis of solubility and affinity for absorption on a solid granular packing column. , Basically, the first step consists of isolation by precipitation of the asphaltenes by adding an excess of alkane solvent (hexane or heptane).…”