Negative-ion Electrospray Ionization Fourier Research Articles

Monitoring the degradation and the corrosion of naphthenic acids by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry and atomic force microscopy

Although the term “naphthenic acids” was originally used to describe acids that contain naphthenic rings, today this term is used in a more general sense and refers to all components in the acid extractable fraction. In crude oil, naphthenic acids exist as a complex mixture of compounds with broad polydispersity with respect to both molecular weight and structure. There has been increasing interest in the naphthenic acids in crude oil because of the corrosion problems that cause during oil refining. Herein, two powerful analytical tools, negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry, ESI(-)FT-ICR MS and atomic force microscopy (AFM), were combined to monitor the thermal degradation of naphthenic acids and their corrosion effects on AISI 1020 steel, respectively. Two different acidic crude oils (TAN=2.38 and 4.79mgKOHg−1, and total sulfur=0.7993 and 1.0220wt%) have been submitted to thermal treatment at 280, 300 and 350°C during 2, 4 and 6h, and characterized by ESI(-)-FT-ICR MS, total acid number (TAN), and total sulfur. The AISI 1020 steel was analyzed by scanning electron microscopy (SEM) and AFM. Generally, heating the crude oil at 350°C in a period of 6h, it was observed that a high efficiency (≅80%) and selectivity of thermal decarboxylation process was monitored by decay of TAN (4.79→0.44mgKOHg−1). ESI(-)-FT-ICR MS results showed that naphthenic acid species remained after the heating have DBE ranging 1–12 and carbon number from C15 to C45. AFM topographic profile evidenced that the naphthenic acid corrosion of the crude oil with TAN of 4.73mgKOHg−1 on AISI 1020 steel was profoundly altered and a marked reduction in peak to peak height values (obtained by subtracting the value of the lowest peak by the highest peak in the topographic area examined). Optical images and microphotographs confirmed the presence of irregularities, characterizing the corrosion mechanism as pitting type. The naphthenic corrosion was also evidenced in samples with low TAN value (0.44mgKOHg−1).

Characterization of Saturated Hydrocarbons in Vacuum Petroleum Residua: Redox Derivatization Followed by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Heavy petroleum fractions, which have distinct chemical and physical properties, are becoming important refinery feedstocks. In comparison to aromatic and heteroatom-containing compounds, the saturate compounds in heavy petroleum fractions have rarely been analyzed using recent advanced mass spectrometry methods. In this work, the compositions of saturate fractions derived from six vacuum residua (VR) of different geological origins were determined and compared. Saturate fractions were subjected to ruthenium-ion-catalyzed oxidation (RICO) derivatization and characterized with negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The results showed that the VR-derived saturates consisted of n-paraffins, isoparaffins, and naphthenes with 1–10 rings. The maximum double bond equivalent (DBE) values of species in various VR-derived saturates were similar. The maximum carbon number of VR-derived saturates was up to 100. The maximum carbon numbers of ...

Characterization of Acidic Compounds in Heavy Petroleum Resid by Fractionation and Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Analysis

Negative-ion electrospray ionization (ESI) enabled the direct mass spectrographic analysis of phenols, naphthenic acids, and neutral nitrogen compounds in petroleum fractions without prefractionation; however, ESI results provide few quantitative and structural information about the analytes: the composition of acidic compounds in heavy oil, such as distillate resid, is still unclear. In this study, extrography was used to fractionate oilsands bitumen-derived vacuum-topped bitumen (VTB) and its maltene and asphaltene fractions into multiple subfractions. The molecular compositions of acidic functional compounds in the VTB and its subfractions were analyzed by negative-ion ESI Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Extrographic separation was a necessary step to isolate acidic compounds of various acidities and/or polarities in vacuum resid fractions to achieve a systematic analysis. The results showed that the O2 class species in VTB were highly condensed phenols and carboxylic acids. The maltene fraction contained most of the less condensed naphthenic acids, whereas the asphaltene fraction contained highly condensed carboxylic acids and phenolic compounds with a bouble-bond equivalent (DBE) higher than 6. The presence of acids had no significant impact on the yield of asphaltenes in n-C7 solvent precipitation. Acid-free asphaltene fractions, which account for more than 90 wt % of the asphaltenes, cannot be ionized by negative-ion ESI.

Effects of experimental conditions on the molecular composition of maltenes and asphaltenes derived from oilsands bitumen: Characterized by negative-ion ESI FT-ICR MS

A vacuum topped Canadian oilsands bitumen (VTB) was subjected to solvent precipitation and subsequently characterized by elemental analysis, gel permeation chromatograph (GPC), 1H-NMR spectroscopy and negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Effects of experimental conditions such as solvent types (n-C5, n-C6, and n-C7), solvent purity, and solvent washing time on asphaltenes yields, bulk composition, and molecular composition of detectable heteroatom compounds in ESI source were determined. Elemental nitrogen and sulfur were enriched in asphaltenes while elemental oxygen had comparable content in maltenes and asphaltenes. Molecular composition of asphaltenes varies with separation conditions. The N1 and O1 species identified by ESI FT-ICR MS were enriched in maltenes. The O2 species exhibited two different double bond equivalents (DBE) distributions and solubility in normal paraffin solvents, indicating two types of molecular structures. Multi oxygen atom containing compounds mainly detected in asphaltenes. Compound class distributions are similar for maltenes derived from n-C5, n-C6, and n-C7, as well as for asphaltenes. The cyclic paraffin impurities in normal paraffin solvents had a significant influence on asphaltenes yields and heteroatom molecular composition. A portion of neutral N1 species and acidic O2 species adsorbed on asphaltenes could be dissolved by increasing washing time. Cautions should be exercised when interpreting the properties and composition of asphaltenes obtained with different experimental conditions.

Separation and characterization of petroleum asphaltene fractions by ESI FT-ICR MS and UV-vis spectrometer

Using heptane, toluene, and tetrahydrofuran (THF) as eluant, asphaltenes were fractionated into five fractions based on their polarity and solubility. The molecular composition of polar heteroatom species in both asphaltene and its fractions were analyzed by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The application of UV-vis spectrometer in characterizing asphaltene composition and measuring asphaltene concentration was discussed. About 11.9 wt% asphaltene components adsorbed permanently on silica gel in the extrography column after excessive elution with various solvents. In negative FT-ICR MS, the mass spectra show that acidic and neutral nitrogen-containing compounds such as N1 and N1S1 mainly existe in the first three less polar fractions, while oxygen-containing compounds such as O2, O2S, O2S2, O3, and O4 show high relative abundance in more polar fractions. These results suggest oxygen-containing compounds have stronger adsorption ability with silica gel. It was observed that the double bond equivalence (DBE) distribution of N1 class species in the fractions shifted to higher values while the carbon number shifted to smaller numbers as polarity of fractions increased. This indicates that acidic and neutral N1 compounds with longer carbon chain and less aromaticity have less polarity compared with those with shorter carbon chain and stronger aromaticity. UV-vis absorbance indicats that fractions containing the most aromatic and most polar asphaltene have better absorbance at long wavelength, while the fractions that consist of least aromatic and least polar asphatlenes show high absorbance at short wavelength.

Thermal transformation of acid compounds in high TAN crude oil

The Liaohe crude oil with high total acid number (TAN) was subjected to thermal reaction at 300 °C to 500 °C. Reaction products were collected and analyzed by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to determine acid compounds in the crude oil. The double-bond equivalence (DBE) versus carbon number was used to characterize the oxygenated components in the feed and reaction products. The O2 class which mainly corresponds to naphthenic acids decarboxylated at 350–400 °C, resulting in a sharply decrease in TAN. Phenols (O1 class) are more thermally stable than carboxylic acids. Carboxylic acids were also thermally cracked into smaller molecular size acids, evidenced by the presence of acetic acid, propanoic acid, and butyric acid in the liquid product. These small acid species are strong acids likely responsible for corrosion problems in refineries.

Monitoring the liquid/liquid extraction of naphthenic acids in brazilian crude oil using electrospray ionization FT-ICR mass spectrometry (ESI FT-ICR MS)

Although the term “naphthenic acids” was originally used to describe acids that contain naphthenic rings, today this term is used in a more general sense and refers to all cyclic, acyclic, and aromatic acids in crude oil. In crude oil, naphthenic acids exist as a complex mixture of compounds with broad polydispersity with respect to both molecular weight and structure. Recently, there has been increasing interest in acidic fractions in crude oil because of the corrosion problems that these compounds cause during oil refinery. This corrosion is associated with the total acid number (TAN). However, it has been argued that there is no clear correlation between the TAN and the level of corrosion. Herein, naphthenic acids were extracted from two crude oil samples (TAN=4.95 and 3.19mg KOHg−1) using liquid/liquid extraction with alkaline solutions at three different pHs (pH 7, 10 and 14), thus evaluating the efficiency and selectivity among different acidic extraction methods to prevent future corrosion processes in petroleum industry such as regions of the refineries working. The original oil samples and their naphthenic acidic fractions and residues (washed oil from the acidic extraction) were analyzed using negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) and Fourier transform infrared spectroscopy (FTIR). The TAN and sulfur content were also determined. We observe a decreasing TAN in the original oil with increasing pH (7→14), reaching a value of almost zero at pH 14. Consequently, an intense band at approximately 1700cm−1 was observed for the naphthenic acidic fraction. Fractions produced ESI(−)-FT-ICR MS spectra with average molecular weight distribution, Mw, and m/z values ranging from m/z 200–350 and Mw=270 (for pH 7) to m/z 200–650 and Mw=390 (for pH 14). Therefore, the acidic extraction method at pH 14 was more efficient and the ESI FT-ICR MS analysis reveals that the most abundant naphthenic acids are those with short alkyl chain lengths (<C44) and DBE=3–4. We associate these compounds as responsible for the TAN observed for the original oil.

Characterization of Middle-Temperature Gasification Coal Tar. Part 3: Molecular Composition of Acidic Compounds

Coal tar has been considered as a potential energy alternative because of dwindling supplies of petroleum. To determine if the coal tar could be refined and upgraded to produce clean transportation fuels, detailed investigation of its composition is necessary, particularly for identifying the acidic components that account for about one-quarter of the weight of the coal tar. A middle-temperature coal tar (MTCT) and its fractions were characterized by gas chromatography–mass spectrometry (GC–MS) and negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with different ion transmission modes for high- and low-mass ions. Analytical results of narrow distillation fractions from FT-ICR MS agreed reasonably well with those from GC–MS, although each technique has its own advantages and disadvantages. In this work, FT-ICR MS was demonstrated to be capable of characterizing small molecules of <100 Da using appropriate operation conditions, thus yielding mass distributions to compare to GC–MS results. A continuous distribution in double bond equivalent (DBE) and carbon number was observed with the distillates of increasing boiling point, while the composition of the distillation residue was much more complex than that of distillates. Acidic compounds containing 1–7 oxygen atoms were observed in the MTCT by FT-ICR MS, with O1 and O2 classes being dominant. Various phenolic compounds with 1–4 aromatic rings were identified on the basis of literature references, including some molecules having structures resembling known biomarkers in petroleum and coal.

Lipid profiling for early diagnosis and progression of colorectal cancer using direct‐infusion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Colorectal cancer (CRC) has attracted increasing attention due to its common occurrence and worldwide distribution. Direct-infusion positive and negative ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (DI-ESI(±)-FTICR MS) was applied to analyze the serum metabolites from 52 CRC patients and 52 healthy controls. Metabolites whose inter-group intensities were determined to be statistically significant by univariate and multivariate statistical analyses were further identified by a combination of the Human Metabolome Database, accurate mass measurement, isotopic abundance distribution simulation, and tandem mass spectrometry. Orthogonal partial least square discriminant analysis (OPLS-DA), based on the data from DI-ESI(±)-FTICR MS, revealed a remarkable discrimination among early stage patients, late stage patients, and healthy controls. A total of 15 differentially expressed metabolites were identified and categorized into four lipid classes. Each lipid class demonstrated specific changing trends in CRC progression. Biomarker panel 1 containing palmitic amide, oleamide, hexadecanedioic acid, octadecanoic acid, eicosatrienoic acid, LPC(18:2), LPC(20:4), LPC(22:6), myristic acid and LPC(16:0) achieved excellent diagnostic accuracy with area under the ROC curve (AUC) of 0.991, a sensitivity of 0.981 and a specificity of 1.000 for differentiating early stage patients from healthy controls, which was better than the carcinoembryonic antigen biomarker. Our study revealed that the consideration of CRC stages would be necessary in diagnostic biomarker discovery, as well as that attention should be paid to the facile loss of methyl chloride from the [M + Cl](-) form of LPC(16:0) in its tandem mass spectrum.

Characterization of Acidic Compounds in Vacuum Gas Oils and Their Dewaxed Oils by Fourier Transform-Ion Cyclotron Resonance Mass Spectrometry

The acidic components in vacuum gas oil (VGO) of cut-2, cut-3, and cut-4 and their corresponding dewaxed oils from a refinery were characterized by negative-ion electrospray ionization (ESI) Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). The acidic heteroatom compounds, N1, N2, N1O1, N1O2, O1, and O2 class species, were identified. Among them, the abundance of O2, O1, and N1 class species were much higher than other acidic class species and characterized by double-bond equivalent (DBE) values and carbon numbers. The N1, N2, N1O1, and N1O2 classes were only identified in VGO cuts instead of dewaxed VGOs. The composition of acidic compounds in VGOs and dewaxed VGOs were correlated with increased boiling point and varied in DBE and carbon numbers. For all identified naphthenic acids, polycyclic naphthenic acids were dominant in VGO cuts, while in their dewaxed oils, naphthenic acids with single-ring were dominant. The most abundant O1 class species had DBE values of 4 corresponding to alkyl phenols in three VGO cuts as well as in three dewaxed VGOs. The abundant N1 class species in three VGO fractions were centered at DBE values of 9 and 12, and these species were likely carbazoles and benzocarbazoles, respectively, while the N1 class species with a DBE of 9 were dominant in three dewaxed VGOs.

Characterization of Red Pine Pyrolysis Bio-oil by Gas Chromatography–Mass Spectrometry and Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

A red pine fast pyrolysis bio-oil was subjected to sequential solvent fractionation into n-hexane soluble (HS), ether soluble (ES), ether insoluble (EIS), dichloromethane soluble (DS), and methanol soluble (MeS) fractions. The volatile components of bio-oil were analyzed by gas chromatography–mass spectrometry (GC–MS), indicating the presence of acids, aldehydes, ketones, alcohols, phenols, and anhydromonosaccharides, which consisted of methoxy, hydroxy, and carbonyl functional groups. These results imply that the bio-oil was similar to the most reported fast pyrolysis bio-oil samples in molecular composition. The bio-oil and its five subfractions were analyzed by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The predominant compounds in bio-oil were O2–O17 class species with 1–22 double-bond equivalent (DBE) values and 4–39 carbon numbers. The most abundant class species in biocrude oil, HS, ES, EIS, DS, and MeS subfractions were O7, O...

Characterization of Pine Pellet and Peanut Hull Pyrolysis Bio-oils by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Pyrolysis of solid biomass, in this case pine pellets and peanut hulls, generates a hydrocarbon-rich liquid product (bio-oil) consisting of oily and aqueous phases. Here, each phase is characterized by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) to yield unique elemental compositions for thousands of compounds. Bio-oils are dominated by Ox species: few oxygens per molecule for the oily phase and many more oxygens per molecules for the aqueous phase. Thus, the increased oxygen content per molecule accounts for its water solubility. Peanut hull bio-oil is much more compositionally complex and contains more nitrogen-containing compounds than pine pellet bio-oil. Bulk C, H, N, O, and S measurements confirm the increased levels of nitrogen-containing species identified in the peanut hull pyrolysis oil by FT-ICR MS. The ability of FT-ICR MS to identify and assign unique elemental compositions to compositionally complex bio-oils based on ultrah...

Analysis of Saturated Hydrocarbons by Redox Reaction with Negative-Ion Electrospray Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

A novel technique was developed for characterization of saturated hydrocarbons. Linear alkanes were selectively oxidized to ketones by ruthenium ion catalyzed oxidation (RICO). Branched and cyclic alkanes were oxidized to alcohols and ketones. The ketones were then reduced to alcohols by lithium aluminum hydride (LiAlH(4)). The monohydric alcohols (O(1)) in the products obtained from the RICO and RICO-LiAlH(4) reduction reactions were characterized using negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) for identification of iso-paraffins, acyclic paraffins and cyclic paraffins. Various model saturated compounds were used to determine the RICO reaction and ionization selectivity. The results from the FTICR MS analysis on the petroleum distillates derived saturated fraction were in agreement with those from field ionization gas chromatography time-of-flight mass spectrometry (FI GC-TOF MS) analysis. The technique was also used to characterize a petroleum vacuum residue (VR) derived saturates. The results showed that the saturated molecules in the VR contained up to 11 cyclic rings, and the maximum carbon number was up to 92.

ANALYSIS AND IDENTIFICATION OF OXYGEN COMPOUNDS IN LONGKOU SHALE OIL AND SHENMU COAL TAR

Methods of acid-base separation and extrography were used to decompose shale oil of Longkou oil shale (LSO), Shandong province, and coal tar of Shenmu coal (SCT), Shanxi province, both China, into acid, base and neutral fractions. The molecular structure and mass distribution of the oxygen compounds present in LSO and SCT were investigated using gas chromatography-mass spectrometry (GC-MS) and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The results of GC-MS showed that oxygen compounds in the acid fractions of LSO and SCT were phenols, indanols, naphthols, phenylphenols, fluorenols and phenanthrenols, and their derivatives, while oxygen compounds in neutral fractions 4 and 5 were aliphatic ketones, esters and minor aromatic ketones. The results of ESI FT-ICR MS demonstrated that in LSO, O1, O2, O3, N1O1, N1O2, N1 and N2 compounds were determined with O1 and O2 compounds as the most abundant. SCT contained O1, O2, O3, O4, O5 and O6 compounds, while O2 and O3 compounds dominated.

Partitioning of Crude Oil Acidic Compounds into Subfractions by Extrography and Identification of Isoprenoidyl Phenols and Tocopherols

Crude oil was subjected to extrography to obtain various acid compounds in multiple subfractions. Negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) and gas chromatography–mass spectrometry (GC–MS) were used to determine the acid compounds in the crude oil subfractions. Isoprenoidyl phenols with molecular formulas of C27H48O and C28H50O, which were previously deduced as sterol-type compounds, were highly enriched in a subfraction and confirmed by GC–MS. The mass peak with a molecular formula of C27H46O2 was identified as δ-tocopherol. The eluting sequence of the various compounds in crude oil was N1 carbazoles, followed by O1 class acid compounds, then O2 class acid compounds, and finally, N1O2, O3, and O4 class acid compounds. The results show that extrography is an adequate separation technique for partitioning crude oil acid compounds into various subfractions.

Influence of Nonbasic Nitrogen Compounds and Condensed Aromatics on Coker Gas Oil Catalytic Cracking and Their Characterization

Contrastive fluid catalytic cracking (FCC) performances of coker gas oil (CGO) narrow-boiling fractions before and after HCl aqueous solution and furfural further treatment were investigated. Nonbasic nitrogen compounds and condensed aromatics in test oil samples were identified by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) and gas chromatography and mass spectrometry (GC–MS), respectively. The results show that basic nitrogen compounds mainly retard the feed conversion and liquid products due to their interaction with Brønsted acid sites or Lewis acid sites during catalytic cracking reactions, while the nonbasic nitrogen compounds and condensed aromatics are hard to convert into smaller molecules, just resulting in obvious effects on yields of gasoline and diesel. Moreover, nonbasic nitrogen compounds with single N species are dominant in CGO, identified as carbazoles, cycloalkyl-carbazoles, benzocarbazoles, and cycloalkyl-benzocarbazoles. Condensed aromatics include three to four rings of large dynamic size, usually presented as chrysene, pyrene, and phenanthrene. These compounds deposit on the surface of catalysts and thus redundant coke is formed; consequently, entrances for other hydrocarbons into acid centers are jammed.

Metabolite Profiling of Triterpene Saponins in Medicago truncatula Hairy Roots by Liquid Chromatography Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Triterpenes are one of the largest classes of plant natural products, with an enormous variety in structure and bioactivities. Here, triterpene saponins from hairy roots of the model legume Medicago truncatula were profiled with reversed-phase liquid chromatography coupled to negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (LC ESI FT-ICR MS). Owing to the accuracy of the FT-ICR MS, reliable molecular formulas of the detected compounds could be predicted, which, together with the generated MS(n) spectra, allowed the tentative identification of 79 different saponins, of which 61 had not been detected previously in M. truncatula. Upon collision-induced dissociation of saponins that contain a uronic acid residue in the sugar chain, fragment ions resulting from cross-ring cleavages of the uronic acid residues were observed. The identified saponins are glycosides of 10 different sapogenins, of which three were not detected before in M. truncatula. Zanhic acid glycosides, which are prevalent in the aerial parts of M. truncatula, were absent in the hairy root extracts. This metabolite compendium will facilitate future functional genomic studies of triterpene saponin biosynthesis in M. truncatula.

Tracking Neutral Nitrogen Compounds in Subfractions of Crude Oil Obtained by Liquid Chromatography Separation Using Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Neutral nitrogen compounds have been used as molecular markers for tracking secondary oil migration in geochemistry. However, the distribution of neutral nitrogen compounds in the separation process is not well-characterized because the conventional analytical technique, such as gas chromatography−mass spectrometry (GC−MS), is non-selective for neutral nitrogen and not capable of detecting non-volatile high-molecular-weight compounds. In this paper, a crude oil was subjected to the traditional two-step open-column liquid chromatography (LC) technique to prepare subfractions, which were characterized for their molecular composition of neutral nitrogen compounds by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The results showed that the two-step LC technique produced a low yield of carbazole in the neutral nitrogen fraction. The neutral nitrogen fraction was enriched with low-molecular-weight neutral nitrogen compounds. Most N1 class speci...

Distribution of Acids and Neutral Nitrogen Compounds in a Chinese Crude Oil and Its Fractions: Characterized by Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

A Chinese crude oil was distilled into multiple narrow boiling fractions. The crude oil, 39 narrow distillate fractions (up to 560 °C), and atmospheric and vacuum residues were analyzed using negative electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The heteroatoms, N1, N2, N1O1, N1O2, O1, and O2 class species, were identified and characterized by double-bond equivalent (DBE) values and carbon numbers. The composition of crude oil was correlated with increased boiling point. Most abundant O1 and O2 class species had DBE values and carbon numbers corresponding to biological skeleton structures, such as hopanoic acid, secohopanoic acid, and sterol. The distribution of acids and neutral nitrogen compounds in the various fractions were determined. At higher carbon numbers, the amount of the compounds and DBE values increased gradually with the boiling point for most oil fractions. The abundant N1 class species were centered at DBE values of 9, 12, 15, and 18...

Characterization of naphthenic acids in crude oils and naphthenates by electrospray ionization FT-ICR mass spectrometry

We present the selective ionization of acidic components of crude oils and naphthenates by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We further characterize isolated naphthenic acids from a calcium napthenate deposit by negative-ion ESI tandem mass spectrometry (MS n): collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD). Selective ionization by electrospray affords direct characterization of neutral nitrogen species and naphthenic acids in petroleum without derivatization or preconcentration of the sample, and with minimal sample consumption. Acids isolated from a calcium naphthenate deposit are tetraprotic with a C 80 hydrocarbon skeleton; commonly known as “ARN” acids, whereas sodium naphthenate consists of low molecular weight (C 15 to C 35) linear saturated monoprotic carboxylic acids. IRMPD and CID fragmentation of ARN acids result in both dehydration and decarboxylation of the carboxylic acid groups without dealkylation. However, CID produced more extensive fragmentation leading to dealkylation of the hydrocarbon skeleton. The ultrahigh resolution and mass accuracy of FT-ICR MS and MS/MS provide for detailed identification and compositional differences of acidic species in crude oils and naphthenates, and also afford structural characterization of acids isolated from naphthenate deposits.