Compositional elucidation of heavy petroleum base oil by GC × GC‐EI/PI/CI/FI‐TOFMS

Comprehensive two‐dimensional gas chromatography (GC × GC) coupled to time‐of‐flight mass spectrometry is a powerful separation tool for complex petroleum product analysis. However, the most commonly used electron ionization (EI) technique often makes the identification of the majority of hydrocarbons impossible due to the exhaustive fragmentation and lack of molecular ion preservation, prompting the need of soft‐ionization energies. In this study, three different soft‐ionization techniques including photo ionization (PI), chemical ionization (CI), and field ionization (FI) were compared against EI to elucidate their relative capabilities to reveal different base oil hydrocarbon classes. Compared with EI (70 eV), PI (10.8 eV) retained significant molecular ion (M^+·) information for a large number of isomeric species including branched‐alkanes and saturated monocyclic hydrocarbons along with unique fragmentation patterns. However, for bicyclic/polycyclic naphthenic and aromatic compounds, EI played upper hand by retaining molecular as well as fragment ions to identify the species, whereas PI exhibited mainly molecular ion signals. On the other hand, CI revealed selectivity towards different base oil groups, particularly for steranes, sulfur‐containing thiophenes, and esters, yielding protonated molecular ions (M + H)⁺ for unsaturated and hydride abstracted ions (M‐H⁺) for saturated hydrocarbons. FI, as expected, generated intact molecular ions (M^+·) irrespective to the base oil chemical classes. It allowed elemental composition by TOFMS with a mass resolving power up to 8000 (FWHM) and a mass accuracy of 1 mDa, leading to the calculation of heteroatomic content, double bond equivalency, and carbon number of the compounds. The qualitative and quantitative results presented herein offer a unique perspective into the detailed comparison of different ionization techniques corresponding to several hydrocarbon classes.     

Electrospray ionization mass spectral 3nvestigations on multi-nuclear complexes of an azacryptand

The electrospray ionization (ES) mass spectrum of a trisodium azacryptate derived from a template reaction of sodium 2,6-diformyl-4-methylphenolate (sdmp) with 2,2′,2″-triaminoethylamine (tren) was investigated and compared with those by fast atom bombardment (FAB), atmospheric pressure chemical ionization (APCI) and electronic ionization (EI) methods. Dinuclear transition metal complexes of this hexaimine macrobicyclic ligand obtained by transmetallation were also studied by ES mass spectra. An [M₂L]⁺ species has been observed for divalent metal complexes, and an [MLH]⁺ species for a trivalent metal complex. The possible mechanism of the fragmentation process is discussed.     

Electron impact,electron capture negative ionization and positive chemical ionization mass spectra of organophosphorus flame retardants and plasticizers

Phosphate esters are important commercial products that have been used both as flame retardants and as plasticizers. To analyze these compounds by gas chromatographic mass spectrometry, it is important to understand the mass spectra of these compounds using various ionization modes. This paper is a systematic overview of the electron impact (EI), electron capture negative ionization (ECNI) and positive chemical ionization (PCI) mass spectra of 13 organophosphate esters. These data are useful for developing and optimizing analytical measurements. The EI spectra of these 13 compounds are dominated by ions such as H₄PO₄⁺, (M ? Cl)⁺, (M ? CH₂Cl)⁺ or (M)⁺ depending on specific chemical structures. The ECNI spectra are generally dominated by (M ? R)^?. The PCI spectra are mainly dominated by the protonated molecular ion (M + H)⁺. The branching of the alkyl substituents, the halogenation of the substituents and, for aromatic phosphate esters, ortho alkylation of the ring are all significant factors controlling the details of the fragmentation processes. EI provides the best sensitivity for the quantitative measurement of these compounds, but PCI and ECNI both have considerable qualitative selectivity. Copyright © 2013 John Wiley & Sons, Ltd.     

Electron ionization and chemical ionization mass spectra of pyridinium and isoquinolinium ylides

Electron ionization (EI) spectra and both positive and negative chemical ionization (CI) spectra have been obtained for four isoquinolinium ylides and two pyridinium ylides. Electron transfer reactions dominate the CI mass specra. The base peak in negative chemical ionization is the [M]^?· ion, formed by electron capture. In the positive methane CI spectra the molecular ion, [M]^+·, is relatively more intense than [MH]⁺ showing electron transfer to be the main positive ionization process. In the positive ammonia CI spectra, proton transfer to give [MH]⁺ is the main ionization process, but electron transfer is also observed. The EI spectra show fragmentations in which the aromatic nitrogen moiety retains the charge and fragmentation is by loss of radicals or small neutral molecules from the side-chains. Radical driven reactions are proposed to explain these spectra.     

APCI as an innovative ionization mode compared with EI and CI for the analysis of a large range of organophosphate esters using GC‐MS/MS

Organophosphate esters (OPEs) are chemical compounds incorporated into materials as flame‐proof and/or plasticizing agents. In this work, 13 non‐halogenated and 5 halogenated OPEs were studied. Their mass spectra were interpreted and compared in terms of fragmentation patterns and dominant ions via various ionization techniques [electron ionization (EI) and chemical ionization (CI) under vacuum and corona discharge atmospheric pressure chemical ionization (APCI)] on gas chromatography coupled to mass spectrometry (GC‐MS). The novelty of this paper relies on the investigation of APCI technique for the analysis of OPEs via favored protonation mechanism, where the mass spectra were mostly dominated by the quasi‐molecular ion [M + H]⁺. The EI mass spectra were dominated by ions such as [H₄PO₄]⁺, [M–R]⁺, [M–Cl]⁺, and [M–Br]⁺, and for some non‐halogenated aryl OPEs, [M]^+● was also observed. The CI mass spectra in positive mode were dominated by [M + H]⁺ and sometimes by [M–R]⁺, while in negative mode, [M–R]⁻ and more particularly [X]^‐ and [X₂]^‐● were mainly observed for the halogenated OPEs. Both EI and APCI techniques showed promising results for further development of instrumental method operating in selective reaction monitoring mode. Instrumental detection limits by using APCI mode were 2.5 to 25 times lower than using EI mode for the non‐brominated OPEs, while they were determined at 50‐100 times lower by the APCI mode than by the EI mode, for the two brominated OPEs. The method was applied to fish samples, and monitored transitions by using APCI mode showed higher specificity but lower stability compared with EI mode. The sensitivity in terms of signal‐to‐noise ratio varying from one compound to another. Copyright © 2016 John Wiley & Sons, Ltd.     

Microsynthesis and mass spectral study of Chemical Weapons Convention related 2‐alkyl‐1,3,6,2‐dioxathiaphosphocane‐2‐oxides

Chemical Weapons Convention (CWC)‐related compounds where the phosphorus atom is part of a ring have very limited representation in mass spectral libraries and the open literature. Here we report electron ionization (EI), chemical ionization (CI) and electrospray ionization tandem mass spectrometry (ESI‐MSⁿ) spectra and retention indices for 2‐alkyl‐1,3,6,2‐dioxathiaphosphocane‐2‐oxides (alkyl C₁ to C₃) which are new cyclic chemicals covered under the CWC. The EI mass spectra show a pattern of ion fragmentation that is similar to that of other cyclic phosphonates in that loss of the alkylphosphonic acid as a neutral loss is more important than the presence of the protonated alkylphosphonic acid. In contrast to other cyclic phosphonates, the 2‐alkyl‐1,3,6,2‐dioxathiaphosphocane‐2‐oxides show almost no protonated alkylphosphonic acid and as a result the spectra do not carry the same distinctive signature of the phosphorus–carbon bond that is required for the chemical to be covered under the CWC. Copyright © 2008 John Wiley & Sons, Ltd.     

Study of the fragmentation pattern of ketamine‐heptafluorobutyramide by gas chromatography/electron ionization mass spectrometry

Ketamine is an anaesthetic compound used in human and veterinary medicine with hallucinogen properties that have resulted in its increased illicit use by teenagers at rave parties. Although several gas chromatography/mass spectrometry (GC/MS) methods have been reported for the quantification of the drug both in urine and in hair, its electron ionization (EI) fragmentation after derivatization with different reagents has been not yet fully investigated. The present work reports the study of the fragmentation of ketamine, derivatized with heptafluorobutyric anhydride (HFBA‐Ket), using gas chromatography/electron ionization mass spectrometry (GC/EI‐MS). The complete characterization of the fragmentation pattern represented an intriguing exercise and required tandem mass spectrometry (MSⁿ) experiments, high‐resolution accurate mass measurements and the use of deuterated d⁴‐ketamine to corroborate the proposed structures and to characterize the fragment ions carrying the unchanged aromatic moiety. Extensive fragmentation was observed, mainly located at the cyclohexanone ring followed by rearrangement of the fragment ions, as confirmed by the mass spectra obtained from the deuterated molecule. The GC/EI‐MS analysis of HFBA‐Ket will represent a useful tool in forensic science since high‐throughput analyses are enabled, preserving both the GC stationary phase and the cleanliness of the mass spectrometer ion optics. Copyright © 2009 John Wiley & Sons, Ltd.     

Electron ionization mass spectrometric study of substituted alloxazine‐5‐oxides and iso‐alloxazine‐5‐oxide

The fragmentation pathways in electron ionization (EI) mass spectra of a series of new N(5)‐oxides of alloxazines and iso‐alloxazine are presented, and compared with those of substituted alloxazines and iso‐alloxazine. The EI mass spectra of these compounds showed characteristic fragmentation pathways A, B and C, started by the ejection of atomic oxygen, a HNCO molecule and an OH ^. radical, respectively. On the basis of B/E and B²/E spectra, the mechanism of elimination of the OH ^. radical is discussed. The influence of the methyl substituent in the benzene ring of alloxazine on the mass fragmentation pathways is described. Copyright © 2009 John Wiley & Sons, Ltd.     

Electron and chemical ionization mass spectrometry in stereochemical differentiation of some 1,3-amino alcohols

Mass spectral fragmentations of two cyclopentane, eight cyclohexane and four norbornane/one 1,3-amino alcohols were studied under electron ionization (EI) by low-resolution, high-resolution, metastable ion analysis and collision-induced dissociation (CID) techniques. All stereoisomeric compounds gave rise to identical 70 eV EI mass spectra. However, the spectra of positional isomers clearly differed. The main fragmentation pathway for the saturated compounds began as an α-cleavage reaction with respect to the nitrogen atom. For the norbornene compounds a retro-Diels—Alder reaction was favoured. Relative to the aminomethyl-substituted compounds the fragmentation patterns for the compounds having the amino group connected directly to the ring were more complicated. The chemical ionization (CI) mass spectra were recorded using ammonia, isobutane, methane, dichloromethane and acetone as reagent gas. From the norbornane/One compounds the di-exo isomers decomposed more easily than the di-endo isomers with most of the reagent gases used. Differences between stereoisomers were observed directly only under methane CI. The decomposition products of the [M + H]⁺ ions generated under ammonia and isobutane CI were studies by recording their CID mass spectra. These spectra allowed the differentiation of the stereoisomers, at least to some extent.     

Differentiation of diastereomeric chlorin derivatives by fast atom bombardment mass spectrometry

The stereochemistry of six pairs of diastereomeric chlorin derivatives was investigated by electron impact (EI), fast atom bombardment (FAB) and direct chemical ionization DCI mass spectrometry. It was demonstrated that FAB and EI mass spectrometry are convenient and rapid methods for distinguishing between diastereomeric chlorin derivatives due to their different fragmentation patterns.     

Fragmentation and rearrangement reactions in certain 1,2,3-triaryl-2-propen-1-ones following electron impact and chemical ionization

The electron impact (EI) and chemical ionization (CI) mass spectra of certain 1,2,3-triaryl-2-propen-1-ones (TAPs) have been studied in detail with the help of exact mass measurements, deuterium labelling and metastable data. The E- and Z-isomeric pairs do not show any difference in their behaviour under EI or CH₄ CI conditions. EI-induced rearangement reactions in the TAPs include aryl migration to carbonium ion centres. A study of the metastable transitions reveals aryl group interchange in the molecular ions prior to fragmentation. Under EI conditions loss of arene involves either C(2) or C(3) aryl groups while under CI conditions the C(1) aryl is lost as a neutral arene molecule. Mechanisms for the different fragmentation modes are given.     

Characteristic features of mass-spectra of some nitroxide radicals

Some compounds containing mono- and polynitroxide radicals have been investigated and characterized by electron ionization (EI), chemical ionization (CI), and matrix-assisted laser desorption-ionization (MALDI) mass spectrometry. Some characteristics of the mass spectra of these radicals are demonstrated. It was found that, under CI and MALDI conditions, ions [M+nH]⁺ are formed along with monoprotonated molecules [M+H]⁺, depending on the type of the radical n = 2–5.     

Formation of M+. ions under matrix fast atom bombardment conditions: Does charge exchange reaction occur?

The formation of molecular ions, M^+., under fast atom bombardment (FAB) conditions using a liquid matrix was examined by using a new type of synthesized compounds in which preferential M^+. peaks appear in their FAB spectra. The FAB spectra were compared with the corresponding mass spectra obtained by the electron impact (EI) ionization, chemical ionization (CI) and charge-exchange ionization (CEI) methods. All of the spectra showed preferential peaks of M^+. ion and a characteristic intense fragment ion peak originating from a β-fission. The FAB spectra were similar in the fragment ions appearing in the EI spectra and were very similar in the fragmentation pattern to the CEI spectra using Ar^+. and Xe^+. as the reagent ions. Further, the FAB spectra did not show any doubly charged ion peaks, while the 70 eV EI spectra showed the peaks of doubly charged molecular and/or fragment ions. The isobutane CI spectra of the synthesized compounds suggested that the formation of M^+. ions occurred through the CE reaction with isobutane ion, C₄H₁₀^+., and the CI spectra showed a marked intense fragment ion peak originating from the β-fission which seemed to occur characteristically in CEI processes. The results obtained suggested that the formation of M^+. ions under matrix FAB conditions occurred mainly by CE reactions between the analytes M and matrix molecular ions B^+. and/or fragment ions b^+..     

Electron impact and chemical ionization mass spectra of 2,2-diphenyl-3-arylcyclobutanone oximes. Formation of ion m/z 167

The electron impact (EI) and chemical ionization (CI) spectra of 2,2-diphenyl-3-aryl cyclobutanone oximes (1–5) are reported. Formation of diphenylmethyl cation at m/z 167 is a major fragmentation process in both EI and CI spectra. Labelling studies established that the hydrogen involved in this rearrangement transfers from the NOH group and not from cyclobutane ring positions. The [M + 3]⁺ ions are formed under CI conditions as a result of C?N double bond reduction. An interesting secondary kinetic isotope effect is observed in the formation of ion e at m/z 183 in both EI and CI spectra. Other characteristic fragmentation pathways occurring in the EI and CI spectra of these compounds are outlined.     

Electron impact and chemical ionization mass spectra of nitro-substituted polyfunctional isomers

The electron impact and methane and ammonia chemical ionization mass spectra of some selected nitro-substituted isomeric benzalacetophenones, benzyl ketones and aromatic epoxides have been examined. The isomeric pairs show significant differences in the electron impact and chemical ionization spectra. The EI spectra show cleavage α to the carbonyl as the major fragmentation mode. Under CI conditions subtle differences in the fragmentation modes of isomeric pairs are more enhanced, and elimination reactions are more favoured in the o-nitro-substituted compounds than in the para isomers.     

Gas phase reactivity of cation radicals and protonated species from isomeric C4H8S thioethers

Four isomeric thioethers, 2,3-dimethylthiirane ( 1 ), 2-methylthietane ( 2 ), tetrahydrothiophene ( 3 ), and allyl methyl thioether ( 4 ), have been subjected to mass spectrometric analysis in the gas phase, under electron impact (El) and chemical ionization (CI) conditions. The metastable molecular ions M⁺′ generated from 1-4 under EI (70 eV) conditions give distinct patterns of unimolecular fragmentation, thus indicating that isomer interconversion reactions are slower than dissociation (a possible exception, to some extent, is the case of [M₂]⁺′ and [M₂]⁺′). The change of the relative intensities of some prominent peaks with increasing ion lifetime (decomposition within the ion source, the first, and the second field-free regions of the mass spectrometer) is pointed out. Metastable [MH]⁺ ions, generated from 1-4 in chemical ionization experiments with CH₄, all eliminate H₂ and H₂S, although in different relative proportions. In addition to these processes protonated 4 also undergoes loss of C₂H₄ and C₃H₆, likely from a C-protonated structure.     

Use of a hand-portable gas chromatograph-toroidal ion trap mass spectrometer for self-chemical ionization identification of degradation products related to O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX)

The chemical warfare agent O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate (VX) and many related degradation products produce poorly diagnostic electron ionization (EI) mass spectra by transmission quadrupole mass spectrometry. Thus, chemical ionization (CI) is often used for these analytes. In this work, pseudomolecular ([M+H]⁺) ion formation from self-chemical ionization (self-CI) was examined for four VX degradation products containing the diisopropylamine functional group. A person-portable toroidal ion trap mass spectrometer with a gas chromatographic inlet was used with EI, and both fixed-duration and feedback-controlled ionization time. With feedback-controlled ionization, ion cooling (reaction) times and ion formation target values were varied. Evidence for protonation of analytes was observed under all conditions, except for the largest analyte, bis(diisopropylaminoethyl)disulfide which yielded [M+H]⁺ ions only with increased fixed ionization or ion cooling times. Analysis of triethylamine-d₁₅ provided evidence that [M+H]⁺ production was likely due to self-CI. Analysis of a degraded VX sample where lengthened ion storage and feedback-controlled ionization time were used resulted in detection of [M+H]⁺ ions for VX and several relevant degradation products. Dimer ions were also observed for two phosphonate compounds detected in this sample.     

Influence of fluorine atoms on the electron impact and chemical ionization mass spectrometric fragmentation of methyl x-deoxy-x-fluoro-per-O-methyl-β-D-galactopyranosides

Fully methylated methyl x-deoxy-x-fluoro-β-D -galactopyranosides were studied using electron impact (EI) and chemical ionization (CI) mass spectrometry and by gas chromatography (GC)/mass spectrometry. Metastable daughter- and parent-ion measurements and high-resolution measurements were used to evaluate the fragmentation schemes. Both the presence and the position of the electronegative fluorine atom influences the fragmentation pathways of the permethylated compounds. The individual methyl x-deoxy-x-fluoro-per-O-methyl-β-D - galactopy-ranosides have different GC retention times. This, together with the characteristic differences present in the EI or CI (methane or isobutane) mass spectra, allows the location of fluorine in these substances to be unambiguously determined.     

Atmospheric pressure ionization–tandem mass spectrometry of the phenicol drug family

In this work, the mass spectrometry behaviour of the veterinary drug family of phenicols, including chloramphenicol (CAP) and its related compounds thiamphenicol (TAP), florfenicol (FF) and FF amine (FFA), was studied. Several atmospheric pressure ionization sources, electrospray (ESI), atmospheric pressure chemical ionization and atmospheric pressure photoionization were compared. In all atmospheric pressure ionization sources, CAP, TAP and FF were ionized in both positive and negative modes; while for the metabolite FFA, only positive ionization was possible. In general, in positive mode, [M + H]⁺ dominated the mass spectrum for FFA, while the other compounds, CAP, TAP and FF, with lower proton affinity showed intense adducts with species present in the mobile phase. In negative mode, ESI and atmospheric pressure photoionization showed the deprotonated molecule [M–H]^?, while atmospheric pressure chemical ionization provided the radical molecular ion by electron capture. All these ions were characterized by tandem mass spectrometry using the combined information obtained by multistage mass spectrometry and high‐resolution mass spectrometry in a quadrupole‐Orbitrap instrument. In general, the fragmentation occurred via cyclization and losses or fragmentation of the N‐(alkyl)acetamide group, and common fragmentation pathways were established for this family of compounds. A new chemical structure for the product ion at m/z 257 for CAP, on the basis of the MS³ and MS⁴ spectra is proposed. Thermally assisted ESI and selected reaction monitoring are proposed for the determination of these compounds by ultra high‐performance liquid chromatography coupled to tandem mass spectrometry, achieving instrumental detection limits down to 0.1 pg. Copyright © 2013 John Wiley & Sons, Ltd.     

Mass Spectra of Furfuryl Aldoximes and Ketoximes

The mass spectra of 8 furfuryl aldoximes and ketoximes were studied under EI and CI conditions. Complicated fragmentation patterns were obtained in EI conditions, including formation of a furfuryl cation radical, furfuryl cation, and [M-17]⁺. The relatively simple patterns of cleavage resulted in few major ion peaks contributed from the adducts, protonation products, and dehydration products under CH₄-CI and NH₃-CI conditions. Comparison with the spectra of their isomeric amides indicated no evidence that the isomerization took place from oximes before fragmentation in both ionization methods.