Article pubs.acs.org/ac
Tetramethylammonium Hydroxide as a Reagent for Complex Mixture Analysis by Negative Ion Electrospray Ionization Mass Spectrometry Vladislav V. Lobodin,† Priyanka Juyal,† Amy M. McKenna,† Ryan P. Rodgers,*,†,‡ and Alan G. Marshall*,†,‡ †
Ion Cyclotron Resonance Program, National High Magnetic Field Laboratory, 1800 East Paul Dirac Drive, Tallahassee, Florida 32310-4005, United States ‡ Department of Chemistry and Biochemistry, Florida State University, 95 Chieftain Way, Tallahassee, Florida 32306, United States S Supporting Information *
ABSTRACT: Ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) enables the direct characterization of complex mixtures without prior fractionation. High mass resolution can distinguish peaks separated by as little as 1.1 mDa), and high mass accuracy enables assignment of elemental compositions in mixtures that contain tens of thousands of individual components (crude oil). Negative electrospray ionization (ESI) is particularly useful for the speciation of the most acidic petroleum components that are implicated in oil production and processing problems. Here, we replace conventional ammonium hydroxide by tetramethylammonium hydroxide (TMAH, a much stronger base, with higher solubility in toluene) to more uniformly deprotonate acidic components of complex mixtures by negative ESI FTICR MS. The detailed compositional analysis of four crude oils (light to heavy, from different geographical locations) reveals that TMAH reagent accesses 1.5−6 times as many elemental compositions, spanning a much wider range of chemical classes than does NH4OH. For example, TMAH reagent produces abundant negative electrosprayed ions from less acidic and neutral species that are in low abundance or absent with NH4OH reagent. More importantly, the increased compositional coverage of TMAH-modified solvent systems maintains, or even surpasses, the compositional information for the most acidic species. The method is not limited to petroleum-derived materials and could be applied to the analysis of dissolved organic matter, coal, lipids, and other naturally occurring compositionally complex organic mixtures.
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double bonds involving carbon), and carbon number for data visualization and comparison of extremely complex mixtures. However, because of ionization efficiency differences between polar functional groups, ESI inherently limits the types of compounds that can be ionized. Furthermore, highly acidic species (carboxylic acids) can hinder or prevent the detection of more concentrated weakly acidic species (e.g., pyrrolic nitrogen species). Compound classes that are insufficiently acidic or basic (such as thiophenes and hydrocarbons) are either not ionized or ionized with poor efficiency. Thus, there is a need for reagents that can promote the formation of charged analyte molecules spanning a wide pKa range to enhance ionization and improve detection with ESI FTICR MS. Ammonium hydroxide (a weak base with pKb ≈ 4.75 in water18) is widely used in conventional negative ion ESI
lectrospray ionization (ESI) is an efficient technique for the selective speciation of polar compounds in complex mixtures.1 ESI coupled to high-field Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) has emerged as a powerful tool for detailed speciation of polar heteroatomic molecules in crude oils, crude oil distillates, petroleum deposits, dissolved organic material, and lipids, thereby reducing the need for tedious fractionation procedures.2−8 ESI typically generates [M + H]+ or [M − H]− ions at atmospheric pressure via protonation or deprotonation and allows for the direct characterization of most acidic and basic components in petroleum and other complex mixtures.9−15 For petroleum samples, the most basic species (pyridinic nitrogen and sulfoxides) are detected by positive ESI,13 whereas negative electrospray ionizes the most acidic constituents (carboxylic acids and neutral nitrogen (pyrrolic) components).16,17 Determination of elemental composition (CcHhNnOoSs) enables subsequent sorting by heteroatom class (NnOoSs), type (double bond equivalents, DBE = number of rings plus © 2013 American Chemical Society
Received: April 24, 2013 Accepted: July 15, 2013 Published: August 6, 2013 7803
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extends the range of functionality of species accessible by ESI for much more complete compositional coverage.
to deprotonate acidic species but is not efficient for detection of less acidic and neutral components. Quaternary ammonium hydroxides are ion-pairs, [NR4+ + OH−], and are strong electrolytes with basicity comparable to alkali hydroxides (i.e., more than 4 orders higher than that of ammonium hydroxide). Moreover, quaternary ammonium hydroxides have good solubility in both aqueous and organic media. They can deprotonate organic substrates with high pKa values and are especially attractive as an electrospray reagent to remove a proton from a weakly acidic carbon, nitrogen, oxygen, or sulfur atom. Literature examples include deprotonation of carboxylic acids (pKa = 4−5); phenols (pKa ∼ 9); mercaptans (pKa ∼ 11); nitrogen-containing heterocycles, such as carbazole (pKa ∼17); and hydrocarbons, such as cyclopentadiene, indene, fluorene, etc. (pKa 15−33), whose pKa values were measured in DMSO solvent.19 Petroleum crude oil is a highly heterogeneous mixture containing tens of thousands of chemically distinct species, including not only hydrocarbons (saturates and aromatics), but also diverse heteroatomic (nitrogen, sulfur, oxygen) compounds as well as metal (Fe, Ni, V)-containing species.20 Heteroatomic compounds, although much less abundant than hydrocarbons, significantly affect the properties and behavior of crude oil during production and refining.21 For example, petroleum asphaltenes, containing some of the most aromatic and heteroatom-rich compounds, create problems related to deposition in well-bore, production/refining equipment, and within actively produced reservoirs,22 resulting in costly operational delays, shut-downs, and potential reservoir damage. Furthermore, increasingly stringent emission and fuel quality regulations limit the concentrations of sulfur, nitrogen, and aromatics in fuels because nitrogen and sulfur oxides formed during the combustion of N- and S-containing precursors can lead to acid rain. Acidic constituents are associated with the formation of stable emulsions during production and hamper efficient oil recovery and subsequent processing. They also are primarily responsible for corrosion in refineries, oil field equipment, and pipelines.23,24 Moreover, because of their surface activity and marginal water solubility, acidic compounds can leach to wastewater, with adverse environmental consequences.25 Petroleomics is based on the premise that exhaustive chemical speciation of fossil fuels at the molecular level enables correlation with (and ultimately prediction of) properties and behavior. Molecular-level understanding of production and refining processes should lead to improved quality of finished fuels6,7 as well as effects on the environment26 and more judicious use of petroleum resources. Because of its unsurpassed resolution and mass accuracy, Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (MS) allows for unambiguous assignment of molecular formulas for tens of thousands of compositionally different ions in a single mass spectrum.27 FTICR MS is, thus, uniquely valuable for analysis of compositionally complex mixtures, such as crude oil, dissolved organic matter, environmental samples, coal liquids, lipids, and foodstuffs.6,26,28−30 Tetramethylammonium hydroxide (TMAH), a quaternary ammonium base, is a commercially available reagent with much higher basicity than ammonium hydroxide. Here, we present FTICR mass spectra for negative ions generated by electrospray with NH4OH and TMAH solvent modifiers for three crude oils of different geographic origin. We find that TMAH greatly
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EXPERIMENTAL METHODS
Samples. Three crude oils produced or imported into the USA (examples of light, heavy, high sulfur, and high nitrogen content crudes), light-sour West Texas (WTS), North American (NA), and heavy South American (SA) were chosen to investigate the effect of substitution of ammonium hydroxide with tetramethylammonium hydroxide in the electrospray solvent for detection of acidic crude oil species. Bulk properties were: light-sour Texas crude oil, carbon 84.6%, hydrogen 11.8%, nitrogen 0.2%, sulfur 1.58%, total acid number (TAN) = 0.11 mg KOH/(gram of oil); North American crude oil, carbon 84.9%, hydrogen 11.1%, nitrogen 0.7%, sulfur 1.2%, TAN = 0.6 mg KOH/(gram of oil); South American crude oil, carbon 80.3%, hydrogen 9.9%, nitrogen 0.6%, sulfur 3.7%, TAN = 3.7 mg KOH/(gram of oil). Sample Preparation. Methanol and toluene (HPLC grade) were purchased from Sigma Aldrich (St. Louis, MO). TMAH (25 vol% in methanol) and ammonium hydroxide (28 vol% NH3 in water) of the highest commercially available purity were obtained from Fisher-Scientific (Tel: 800-7667000). Each of the crude oil samples was dissolved in a 1:1 (v/ v) solution of toluene/methanol at a concentration of 500 μg/ mL. TMAH and ammonium hydroxide were added to a concentration of 1% by volume. The reagents and sample solutions were vortexed for a few seconds before analysis. A fused-silica micro ESI needle of 50 μm inner diameter (i.d.) delivered each sample to the ionization source via a syringe pump at a rate of 400 nL/min under typical ESI conditions (2.1 kV; tube lens, 350 V, and heated metal capillary operated at ∼10 W).31 Instrumentation, Data Acquisition and Processing. A previously described custom-built FTICR mass spectrometer equipped with a passively shielded 9.4 T superconducting magnet of 225 mm bore diameter provided negative-ion ESI mass spectra of each crude oil sample.32,33 External calibration of the instrument was performed with G2421A electrospray (Agilent, Palo Alto, CA) HP mix. Instrument control and data analysis were performed with a modular ICR data station.34,35 For each sample, 100 time-domain acquisitions were summed, Hanning-apodized, and zero-filled once before fast Fourier transformation and magnitude calculation. The quadrupolar electric trapping potential approximation was used for frequency to mass-to-charge conversion.36,37 Each mass spectrum was internally calibrated with respect to a highly abundant homologous series of ions38 containing two oxygen atoms (NH4OH spiked samples) or one nitrogen atom (TMAH spiked samples). Singly charged ions (200 < m/z < 1400) of mass spectral peak magnitude greater than 6 times the standard deviation of the baseline noise were Kendrick-sorted and imported into Microsoft Excel for identification with a formula calculator, as previously described.9 The mass tolerance was set to ±1 ppm and calculations were limited to elemental compositions containing 100 12C, 200 1H, 2 13C, 5 14N, 10 16O, and 3 32S atoms. Kendrick mass defect was used to identify homologous series and aid in peak assignment. An isoabundance-contoured plot of DBE vs carbon number was constructed for each heteroatom class by use of SigmaPlot 9.0 (Systat Software Inc., San Jose, CA). 7804
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RESULTS AND DISCUSSION
Analyte Acidity. FTICR MS coupled with an appropriate ionization method precludes tedious and time-consuming fractionation and sample preparation and yields comprehensive information about the molecular weight, heteroatom class, type, and carbon number distributions of petroleum compounds. The nonpareil mass accuracy (rms mass error < 500 ppb) and ultrahigh resolution (mass resolving power, m/Δm50% > 400 000, in which Δm50% is the mass spectral peak full width at halfmaximum peak height) of FTICR MS coupled with the selectivity of ESI allows for the rapid identification of polar components of crude oil.12,13,39,40 Negative ESI accesses the acidic fraction of oil by deprotonation to yield [M − H]− ions. It is well-known that acidic components of crude oil are not limited to carboxylic acids, but also include sulfur- and nitrogen-containing molecules. Tomczyk et al. reported that approximately one-half of the acidic species in a highly biodegraded crude oil contained nitrogen, and at least onefourth contained sulfur.41 For carboxylic acids (O2 class), pKa ≈ 4−5, and for sulfur-oxy acids, such as sulfinic acids (S1O2), pKa ≈ 2 (e.g., benzene sulfinic acid, pKa 1.99). Other acidic but noncarboxylic acid functionalities are weakly or moderately acidic with pKa values ranging from 6 to 34. The pKa values for thiophenols and phenols are ∼6.5 and ∼9, and for carbazoles, pKa ≈ 17. Thus, ammonium hydroxide is insufficiently basic to deprotonate species weaker than carboxylic acids so that negative ESI fails to access those weak acids. Even-Mass vs Odd-Mass Species. Figure 1 illustrates the increased compositional complexity afforded by a TMAHmodified electrospray solvent system. The negative ESI FTICR mass spectrum of a high total acid number (TAN = mg KOH required to neutralize 1 g of oil) South American crude oil obtained with an ammonium hydroxide solvent system (Figure 1, top) resolves and identifies slightly more than 5000 acidic species. The same crude oil sample produced from a TMAH solvent system (Figure 1, bottom) exhibits more than 30 000 assigned elemental compositions spanning a significantly wider mass range. TMAH also results in lower relative abundance of odd m/z ions (mainly [M − H]− ions of naphthenic acids, Figure 1, top) to reveal the less basic (nitrogen-containing) species at even m/z values (Figure 1, bottom). Heteroatom Classes. Figure 2 shows the heteroatom class distribution for the South American crude oil, deprotonated with either ammonium hydroxide or TMAH. The relative abundance of acidic components (O2, SO2, and SO3 classes) is considerably higher with ammonium hydroxide, whereas TMAH increases the relative abundance of N1 and N1S1 classes by a factor of at least 5, and the weaker acidic O1 class, the phenols, by a factor of 3. Other weakly acidic classes (NO, NS2, and SO) that are undetectable with ammonium hydroxide are rendered detectable with TMAH. The SO2 and O2 species, the most acidic compound classes in crude oils, are dominant with ammonium hydroxide, but even at their lower relative abundance with TMAH actually yield greater compositional detail (see below). Ionization Efficiency. Deprotonation efficiency of neutral compounds is further diminished as a result of competition for the charge with carboxylic acids. The observed ion relative abundances depend on ionization efficiency of the corresponding compounds and may not correspond to the actual concentration of neutral precursor in the original sample. For example, although O2 class are the most abundant in negative
Figure 1. Broadband FTICR mass spectra of a high total acid number South American crude oil (m/Δm50% = 800 000 at m/z 500) obtained with an ammonium hydroxide-modified solvent system (top) and a tetramethylammonium hydroxide (TMAH)-modified solvent system (bottom) by negative electrospray ionization. TMAH enables the identification of more than six times the number of elemental compositions spanning a wider molecular weight range, and suppresses highly acidic species (of odd mass) to reveal weakly acidic species (nitrogen-containing and hydrocarbons) at even m/z values.
Figure 2. Heteroatom class distributions for the 14 most abundant classes of a South American crude oil analyzed by (−) ESI FTICR MS with NH4OH (blue) and TMAH (red). The most acidic classes, O2 and SO2, are the most abundant with ammonium hydroxide, but are more than 3× lower in relative abundance with the TMAH-modified solvent system, for which N1 (pyrrolic nitrogen) species are the most abundant.
ESI mass spectra for a South American crude oil sample with ammonium hydroxide, carboxylic acids may not be the most abundant acidic components of the parent oil. A stronger basic reagent or solvent system that levels the ionization efficiency for all acidic species would quantify the crude oil profile and provide better insight into the relative composition of acidic 7805
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compound classes and also widen a range of compounds accessible by negative ion ESI. Compositional Characterization. Compositional characterization is facilitated by construction of color-coded isoabundance-contoured plots of double bond equivalents vs carbon number for members of a particular heteroatom class. Figures 3−6 show DBE vs carbon number images for ions from
Figure 4. Isoabundance-contoured DBE versus carbon number plots for ions of the N1 class for three crude oils, obtained by (−) ESI FTICR MS with NH4OH (top) and TMAH (bottom).
Figure 3. Isoabundance-contoured DBE versus carbon number plots for ions of the O2 class for light-sour West Texas (WTS), South American (SA), and North American blend (NA) crudes, obtained by (−) ESI FTICR MS with NH4OH (top) and TMAH (bottom).
each of three crude oils based on negative ion ESI with ammonium hydroxide or tetramethylammonium hydroxide. As described below, the speciation of compound classes varies significantly between the two electrospray solvent systems. Figure 3 demonstrates the difference in O2 class (carboxylic acids) composition between NH4OH and TMAH reagents. For West Texas light-sour and North American crude oils, TMAH accesses a wider range of DBE and carbon numbers. The South American crude oil (characterized by high TAN value and, hence, high carboxylic acid content) exhibits similar relative abundances but only a slightly wider DBE and carbon number range for the TMAH-containing solvent. Ion abundance differences between NH4OH and TMAH reagents are even more pronounced for less acidic heteroatom classes. Figure 4 shows DBE vs carbon number images for ions of the N1 heteroatom class from each of three crude oils, derived from the TMAH or NH4OH reagent. The TMAH reagent clearly generates more N1 class ions over a much wider range of DBE (8−21) and carbon number (20−55) than NH4OH (8−17 and 20−32). N1 class species likely include pyrrole/indole/carbazole-type weak acids, and the higher relative abundance with the TMAH reagent may be ascribed to enhanced deprotonation of these relatively weak acids (pyrrole (pKa 23), indole (pKa 21), carbazole (pKa 19.9)).42 O1 class ions (Figure 5) exhibit an onset at DBE = 4 with both reagents, but TMAH ionizes weak acids extending to higher DBE and carbon numbers. The O1 compounds likely include weakly acidic phenols. Supporting Information Figures S1 and S2 dramatically illustrate the superiority of TMAH over NH4OH as a reagent for deprotonation of N1O1 and N1S1 ion classes. TMAH accesses dozens of South American crude N1O1 class ions that
Figure 5. Isoabundance-contoured DBE versus carbon number plots for ions of the O1 class for three crude oils, obtained by (−) ESI FTICR MS with NH4OH (top) and TMAH (bottom).
are absent with NH4OH (Supporting Information Figure S1). Similarly, for all three crude oils, N1S1 class ions that are underrepresented or absent with NH4OH appear with significant abundance with TMAH (Supporting Information Figure S2). The biggest difference between TMAH and NH4OH reagents is for detection of compounds not containing heteroatoms, namely, hydrocarbon class (HC) ions, which are completely absent in negative ESI with NH4OH. Although aromatic hydrocarbons with a cyclopentadiene ring are very weakly acidic in solution (pKa values measured in DMSO for cyclopentadiene, indene, fluorene are 18, 20, 23), their gasphase acidities exceed that of water.19,43,44 Deprotonation at the sp3 carbon is favored because it results in the formation of a resonance-stabilized aromatic carbanion. Supporting Information Figure S3 summarizes the compositional distributions for CH, NOS, N1S2, N2, S1, and S2 ion classes for light-sour North American crude oil negative ESI FTICR MS with TMAH reagent. Those ion classes are either absent (HC, NOS, NS2, S2 classes) or very low in abundance 7806
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analytes of equimolar concentration from the same class can produce ESI responses differing by orders of magnitude, rendering quantitative analysis difficult.51 The surface affinity of ions is believed to contribute to response differences. The excess negative charge is distributed on the droplet surface as a result of Coulomb repulsion, and ions of lower solubility are prone to concentrate at the liquid−air interface (outer sphere, Figure 6). This effect is especially significant for aqueous media and is less critical for a pure organic mobile phase. However, the droplet solvent composition can differ from the parent bulk solution: during electrospray, solvent polarity in a droplet increases and is enriched in the less volatile component.52,53 The presence of ions with high gas-phase basicity can also influence analyte ionization efficiency because the local environment at the droplet surface partly resembles the gas phase and is different from the bulk solution. In fact, high gasphase basicity of the hydroxide anion in TMAH enables efficient deprotonation of less acidic species in petroleum samples. We tested that hypothesis by comparison with structurally similar modifiers: tetramethylammonium flouride (NMe4+F−) and tetramethylammonium chloride (NMe4+Cl−). Both compounds are strong organic electrolytes, are soluble in organic solvents, and are not basic in solution. Nevertheless, the gas-phase proton affinity (PA) of their anions is very different. For example, PA(F−) is 372 kcal/mol (i.e., ΔrH° = −372 kcal/ mol for the reaction F− + H+ = HF),54 close to the proton affinity of hydroxide anion (PA(OH−) = 390.3 kcal/mol),54 and higher than the gas-phase proton affinity for [M − H]− ions from carbazole (PA = 345.1 kcal/mol), phenol (PA = 349.7 kcal/mol), and cyclohexane carboxylic acid (PA = 345.1 kcal/mol).54 As a result, tetramethylammonium flouride produces similar compositional coverage, despite its low solution-phase basicity. In contrast, (−) ESI experiments with tetramethylammonium chloride did not increase the negative ion yield for the less acidic compounds (N1, N1O1, N1S1 classes) because the gas-phase proton affinity of chloride-ion (PA(Cl−) = 333.4 kcal/mol)54 is below the threshold for their ionization through deprotonation in the gas phase.
(N2, S1 classes) with NH4OH reagent. The hydrocarbon class (HC) ions exhibit DBE = 9−24, corresponding to condensed polycyclic structures. NOS, N1S2, N2 ion classes span a wide range in both DBE (12−30) and carbon number (20−70) and likely contain either pyrollic nitrogen (NOS, N1S2, N2 classes), a thio group (NOS, N1S2 classes), or a phenolic group (NOS class). S1 and S2 ion classes exhibit bimodal DBE distributions: low DBE = 0−3, suggesting thiols, and high DBE = 10−25 that could represent thiophenols (deprotonation of −SH group) or condensed polycyclic sulfur-containing compounds deprotonating by a mechanism similar to that for the HC class (deprotonation of sp3-hybridized carbon adjacent to an aromatic core). Finally, Supporting Information Figure S4 shows color-coded isoabundance-contoured plots of DBE versus carbon number for the S1O1 and S1O2 ion classes for North American blend crude oil derived from negative ion ESI FTICR MS with NH4OH or TMAH reagent. Again, both ion classes extend to higher DBE and higher relative abundance with TMAH than with NH4OH reagent. Ammonium hydroxide deprotonates only the most acidic members of the S1O2 class, such as sulfurcontaining naphthenic acids or sulfinic acids (pKa ∼ 2), whereas the stronger TMAH base can ionize less acidic compounds of this class through deprotonation of phenolic or thio (−SH) groups. Mechanism of Ionization for (−) ESI with TMAH. Electrospray requires production of excess charge on the droplets by electrochemical reactions that occur at the metal− liquid surface in the ESI emitter (Supporting Information Figure S5). For negative ion production, electrochemical reduction of positive ions can originate from solvent, modifier, or impurities.45−48 In any case, addition of a basic modifier for (−) ESI facilitates deprotonation of analyte molecules and increases the concentration of [M − H]− ions in solution. It is known that strong acids or bases (strong electrolytes) can suppress analyte signal during ESI as a result of competition for sites on the droplet surface49 and are not often used as modifiers. In addition to the formation of ions in solution, the efficiency of formation of gas-phase ions during ESI also determines the signal response for analytes. Desorption of ions from the droplet surface by an ion evaporation mechanism is generally accepted for small molecules (Figure 6).45,50 The presence of other analytes and salts can also cause drastic signal suppression as a result of competition for surface sites. Thus,
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CONCLUSIONS We demonstrate that a slight modification of the solvent system for negative ion ESI FTICR MS is extremely effective in expanding the compositional coverage for crude oil acids to a wider range of double bond equivalents and carbon number. The use of ammonium hydroxide as a modifier over-represents the most acidic compound classes (e.g., carboxylic acids), even when they are not the most abundant molecular class in crude oil. Tetramethylammonium hydroxide achieves deprotonation of much less acidic molecules and enables their detection at much lower concentration. (−) ESI with TMAH is not intended to substitute for APPI and APCI; rather, it is a complementary method that provides coverage over a wider range of acidity. Moreover (+) APPI is commonly used for complex mixture analysis and ionizes nonpolar classes (e.g., hydrocarbons) more efficiently than (−) ESI with TMAH. The ionization mechanism for (−) ESI with TMAH is more complex than simple deprotonation of analyte molecules by hydroxide ion. Parameters affecting the signal response include desorption of ions from the droplet surface and their surface affinity, solvent composition, gas-phase basicity, etc., and will be the subject of further studies. NH4OH can still be used if selective ionization of acidic compounds (e.g., naphthenic acids) is desired. (−) ESI with TMAH is a complementary
Figure 6. Schematic representation of a charged droplet and ion evaporation model. The distribution of ions in the inner and outer spheres depends on solvent composition and analyte polarity. For negative ion electrospray, analyte ions are shown in blue, positive counterions in red, and anions from the electrolyte (base, salt, impurities) in green. The electrolyte anions (green) have higher affinity for the surface and preferentially concentrate in the outer sphere, leading to suppression of the signal for analyte ions (blue). 7807
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(20) Speight, J. G. The Chemistry and Technology of Petroleum; 3rd ed.; Marcel Dekker, Inc.: New York, 1999; Vol. 76. (21) Composition and Analysis of Heavy Petroleum Fractions. Chemical Industry; Algelt, K. H., Boduszynski, M. M., Eds.; Dekker: New York, 1994; Vol. 54, p 495. (22) Joshi, N. B.; Mullins, O. C.; Jamaluddin, A.; Creek, J.; McFadden, J. Energy Fuels 2001, 15, 979−986. (23) Jayaraman, A.; Saxena, R. C. Corros. Prev. Control 1995, 42, 123−31. (24) Turnbull, A.; Slavcheva, E.; Shone, B. Corrosion (Houston) 1998, 54, 922−930. (25) Lai, J. W. S.; Pinto, L. J.; Kiehlmann, E.; Bendell-Young, L. I.; Moore, M. M. Environ. Toxicol. Chem. 1996, 15, 1482−1491. (26) Lobodin, V. V.; Rodgers, R. P.; Marshall, A. G. In Comprehensive Environmental Mass Spectrometry; Lebedev, A., Ed.; ILM Publications: St Albans, 2012, pp 415−442. (27) Marshall, A. G.; Hendrickson, C. L.; Jackson, G. S. Mass Spectrom. Rev. 1998, 17, 1−35. (28) Cory, R. M.; McNeill, K.; Cotner, J. P.; Amado, A.; Purcell, J. M.; Marshall, A. G. Environ. Sci. Technol. 2010, 44, 3683−3689. (29) Cooper, H. J.; Marshall, A. G. J. Agric. Food Chem. 2001, 49, 5710−5718. (30) Wu, Z. G.; Rodgers, R. P.; Marshall, A. G. J. Agric. Food Chem. 2004, 52, 5322−5328. (31) Emmett, M. R.; White, F. M.; Hendrickson, C. L.; Shi, S. D. H.; Marshall, A. G. J. Am. Soc. Mass Spectrom. 1998, 9, 333−340. (32) Kaiser, N. K.; Quinn, J. P.; Blakney, G. T.; Hendrickson, C. L.; Marshall, A. G. J. Am. Soc. Mass Spectrom. 2011, 22, 1343−1351. (33) Senko, M. W.; Hendrickson, C. L.; Emmett, M. R.; Shi, S. D. H.; Marshall, A. G. J. Am. Soc. Mass Spectrom. 1997, 8, 970−976. (34) Blakney, G. T.; Hendrickson, C. L.; Marshall, A. G. Int. J. Mass Spectrom. 2011, 306, 246−252. (35) Senko, M. W.; Canterbury, J. D.; Guan, S.; Marshall, A. G. Rapid Commun. Mass Spectrom. 1996, 10, 1839−1844. (36) Ledford, E. B., Jr.; Rempel, D. L.; Gross, M. L. Anal. Chem. 1984, 56, 2744−2748. (37) Shi, S. D. H.; Drader, J. J.; Freitas, M. A.; Hendrickson, C. L.; Marshall, A. G. Int. J. Mass Spectrom. 2000, 195/196, 591−598. (38) Kendrick, E. Anal. Chem. 1963, 35, 2146−54. (39) Rodgers, R. P.; Kim, S.; Klein, G. C.; Wu, Z.; Schaub, T. M.; Marshall, A. G. Prepr. Am. Chem. Soc., Div. Pet. Chem. 2004, 49, 16−17. (40) Rodgers, R. P.; Klein, G. C.; Stanford, L. A.; Kim, S.; Marshall, A. G. FUEL-008. Abstracts of Papers, 228th ACS National Meeting, Philadelphia, PA, United States, August 22−26, 2004,. (41) Tomczyk, N. A.; Winans, R. E.; Shinn, J. H.; Robinson, R. C. Energy Fuels 2001, 15, 1498−1504. (42) Bordwell, F. G.; Drucker, G. E.; Fried, H. E. J. Org. Chem. 1981, 46, 632−635. (43) Dessy, R. E.; Okuzumi, Y.; Chen, A. J. Am. Chem. Soc. 1962, 84, 2899−904. (44) Streitwieser, A., Jr.; Hammons, J. H.; Ciuffarin, E.; Brauman, J. I. J. Am. Chem. Soc. 1967, 89, 59−62. (45) Crotti, S.; Seraglia, R.; Traldi, P. Eur. J. Mass Spectrom. 2011, 17, 85−99. (46) Diehl, G.; Karst, U. Anal. Bioanal. Chem. 2002, 373, 390−398. (47) Meier, L.; Schmid, S.; Berchtold, C.; Zenobi, R. Eur. J. Mass Spectrom. 2011, 17, 345−351. (48) Van Berkel, G. J.; Kertesz, V. Anal. Chem. 2007, 79, 5510−5520. (49) Kuhlmann, F. E.; Apffel, A.; Fischer, S. M.; Goldberg, G.; Goodley, P. C. J. Am. Soc. Mass Spectrom. 1995, 6, 1221−1225. (50) Kebarle, P.; Verkerk, U. H. Mass Spectrom. Rev. 2009, 28, 898− 917. (51) Wu, Z. R.; Gao, W. Q.; Phelps, M. A.; Wu, D.; Miller, D. D.; Dalton, J. T. Anal. Chem. 2004, 76, 839−847. (52) Wang, R.; Zenobi, R. J. Am. Soc. Mass Spectrom. 2010, 21, 378− 385. (53) Zhou, S. L.; Cook, K. D. Anal. Chem. 2000, 72, 963−969. (54) http://webbook.nist.gov/chemistry/.
method and provides more coverage for less acidic classes (e.g., N1, N1S1, etc.).
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ASSOCIATED CONTENT
S Supporting Information *
Additional information as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*Phone: +1 850 644 0529 (A.G.M.), +1 850 644 2398 (R.P.R.). Fax: +1 850 644 1366. E-mail:
[email protected] (A.G.M.),
[email protected] (R.P.R.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by NSF Division of Materials Research through DMR 11-57490, BP/The Gulf of Mexico Research Initiative, the Florida State University Future Fuels Institute, Nalco (An Ecolab Company), and the State of Florida.
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REFERENCES
(1) Zhan, D.; Fenn, J. B. Int. J. Mass Spectrom. 2000, 194, 197−208. (2) Marshall, A. G.; Kim, D.-G.; Klein, G. C.; Stanford, L. A.; Purcell, J. M.; Schaub, T. M.; Smith, D. F.; Hendrickson, C. L.; Rodgers, R. P. In Abstracts of Papers, PETR-167, 232nd ACS National Meeting, San Francisco, CA, United States, Sept. 10−14, 2006. (3) Marshall, A. G.; Rodgers, R. P. Acc. Chem. Res. 2004, 37, 53−59. (4) Fu, J.-M.; Kim, S.; Hendrickson, C. L.; Rodgers, R. P.; Marshall, A. G.; Qian, K. Energy Fuels 2006, 20, 661−667. (5) Klein, G. C.; Angström, A.; Rodgers, R. P.; Marshall, A. G. Energy Fuels 2006, 20, 668−672. (6) Rodgers, R. P.; Marshall, A. G. In Asphaltenes, Heavy oils, and Petroleomics; Mullins, O. C., Sheu, E. Y., Hammani, A., Marshall, A. G., Eds.; Springer: New York, 2007, pp 63−89. (7) Rodgers, R. P.; Schaub, T. M.; Marshall, A. G. Anal. Chem. 2005, 77, 20A−27A. (8) Klein, G. C. Electronic Theses, Treatises and Dissertations, Paper 2822, Florida State University, 2005. (9) Hughey, C. A.; Hendrickson, C. L.; Rodgers, R. P.; Marshall, A. G.; Qian, K. Anal. Chem. 2001, 73, 4676−81. (10) Hughey, C. A.; Rodgers, R. P.; Marshall, A. G. Anal. Chem. 2002, 74, 4145−4149. (11) Hughey, C. A.; Rodgers, R. P.; Marshall, A. G.; Qian, K.; Robbins, W. K. Org. Geochem. 2002, 33, 743−759. (12) Qian, K.; Robbins, W. K.; Hughey, C. A.; Cooper, H. J.; Rodgers, R. P.; Marshall, A. G. Energy Fuels 2001, 15, 1505−1511. (13) Qian, K.; Rodgers, R. P.; Hendrickson, C. L.; Emmett, M. R.; Marshall, A. G. Energy Fuels 2001, 15, 492−498. (14) Smith, D. F.; Schaub, T. M.; Rahimi, P.; Teclemariam, A.; Rodgers, R. P.; Marshall, A. G. Energy Fuels 2007, 21, 1309−1316. (15) Stanford, L. A.; Kim, S.; Rodgers, R. P.; Marshall, A. G. Energy Fuels 2006, 20, 1664−1673. (16) Hughey, C. A.; Rodgers, R. P.; Marshall, A. G.; Walters, C. C.; Qian, K.; Mankiewicz, P. Org. Geochem. 2004, 35, 863−880. (17) Kim, S.; Stanford, L. A.; Rodgers, R. P.; Marshall, A. G.; Walters, C. C.; Qian, K.; Wenger, L. M.; Mankiewicz, P. Org. Geochem. 2005, 36, 1117−1134. (18) Weast, R. C.; Astle, M. J.; Beyer, W. H. CRC Handbook of Chemistry and Physics, 69th ed.; CRC Press Inc.: Boca Raton, 1988. (19) Starks, C. M.; Liotta, C. L.; Halpern, M. Phase Transfer Catalysis: Fundamentals, Applications, and Industrial Perspectives; Chapman & Hall: New York, 1994. 7808
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