Combination of Negative Electrospray Ionization and Positive Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry as a Quantitative Approach of Acid Species in Crude Oils

Abstract

Crude oils differ from one another in numerous chemical and physical properties, many of which play an important role in defining their quality and price. Generally, statistical analysis of price differentials has focused on two main properties: density and sulfur content. However, the growing significance of high total acid number (TAN) crude oils, especially from developing countries, has aroused the necessity for extending these models. Consequently, refineries must obtain real and exact information regarding crude oil quality to achieve optimal crude oil selection and processing decisions. This could be attained when a detailed molecular-level characterization is performed. The present work presents the combination of negative electrospray ionization [(−)­ESI] and positive atmospheric pressure photoionization [(+)­APPI] Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, as a prominent approach to semi-quantify the acid species comprised in crude oils. A novel polarity index is proposed that corrects the relative abundances of (−)­ESI classes, where mainly acid species are detected. By consideration of different indexes, it was possible to enhance the correlation coefficients (R 2) from 0.579 to 0.986 between the percentage of acid compounds and TAN of crude oils, where most of the samples stand close to a linear tendency. These results avoid the deviations observed in previous works on the correlations between relative abundances of the O2 class through (−)­ESI and TAN and could support achieving optimal crude oil selection and defining their quality and price.

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

“…32 In agreement with our results, the same optimal accumulated scans have also been reported. 15,32,33 Some studies have, however, applied twice as high accumulated scans, 200, but we found that accumulated scans above 100 results in MS with similar quality. 34,35 Some studies have described the use of sheath, auxiliary and sweep gases in crude oil analysis by APPI(±)-MS, but the values cannot be found in the manuscripts.…”

“…34,35 Some studies have described the use of sheath, auxiliary and sweep gases in crude oil analysis by APPI(±)-MS, but the values cannot be found in the manuscripts. 15,31,32…”

“…[9][10][11][12] ESI FT-ICR MS has, therefore, been widely used to determine sulfurcontaining species in heavy crude oil 13 and non-polar polyaromatic hydrocarbons and polyaromatic heterocycles in asphaltenes, 10,14 as well as to classify biodegraded and non-biodegraded crude oils focused on the O 2 -class. 12 Atmospheric pressure photoionization (APPI) has also been applied to crude oil analysis, [15][16][17] but much less intensively, most particularly when the goal is to efficiently ionize nonpolar sulfur species and polycyclic aromatic hydrocarbons, which are interesting classes because they affect the petroleum refinery and its regulation by governmental agencies. 18 The direct infusion of crude oil solutions on APPI can positively charge species to produce both radical cations (M +• ) and protonated molecules ([M + H] + ) 18 by APPI(+) acquisition mode or negatively to produce deprotonated molecules ([M -H] -) by APPI(-) acquisition mode.…”

Recent Advances in Petroleum Analysis by Mass Spectrometry

“…The need to characterize NAs is driven by environmental and crude oil processing reasons because, despite their low abundance in crude oils, NAs are the main corrosive species in acidic crude oils. , Additionally, NAs are the major contributor to the total acid number of a crude oil. A high total acid number reduces the value of a crude oil because this causes corrosion and other refinery problems. , Thermal degradation of crude oil has been reported to reduce its total acid number because this process can decarboxylate NAs . It is possible that decarboxylation of NAs can be improved if NAs are better characterized.…”

“…A high total acid number reduces the value of a crude oil because this causes corrosion and other refinery problems. 118,119 Thermal degradation of crude oil has been reported to reduce its total acid number because this process can decarboxylate NAs. 120 It is possible that decarboxylation of NAs can be improved if NAs are better characterized.…”