Electron Ionization Mass Spectra Research Articles

Scent Chemicals of the Tail Gland of the Red Fox,Vulpes vulpes

Like all animals, the red fox uses chemical signals for social communication. The supracaudal or tail gland smells of violets, attributed to the presence of carotenoid degradation products, or apocarotenoids, which commonly occur as aromatics in flowers. We have more fully characterized the scent chemistry of the fox tail gland. Volatile chemicals were analyzed by gas chromatography-mass spectrometry (GC-MS) and identified from their electron ionization mass spectra and Kovats retention indices. The 3 previously reported apocarotenoids were confirmed, and many additional compounds found. These include the apocarotenoids β-cyclocitral, β-homocitral, β-ionone, cyclic β-ionone, β-ionone-5,6-epoxide, α-ionene, α-ionone, 2,6,6-trimethylcyclohexanone (IUPAC 2,2,6-), 2,6,6-trimethyl-2-cyclohexen-1-one, 6-methyl-5-hepten-2-one (sulcatone), and geranyl acetone. Notably, sulcatone is a semiochemical in several species. 3,3-Dimethyl-2,7-octanedione was identified as a probable apocarotenoid which is likely to be a significant fox scent chemical. The γ-lactone of 4-hydroxyhexadecanoic acid (hexadecan-4-olide) was also found, one of a group of known mammalian signaling compounds. This rich mixture of volatile apocarotenoids implies an adequate consumption of plant carotenoids, which are known to be necessary for optimal health. Dietary carotenoids color the skin and feathers of some birds, used as a visual signal to conspecifics, and the floral aroma of the fox tail gland may provide an olfactory signal to other foxes.

Evaluation of a liquid electron ionization liquid chromatography–mass spectrometry interface

Liquid Electron Ionization (LEI), is an innovative liquid chromatography-mass spectrometry (LC–MS) interface that converts liquid HPLC eluent to the gas-phase in a mass spectrometer equipped with an electron ionization (EI) source. LEI extends the electronic spectra libraries access to liquid chromatography, providing a powerful tool in the untargeted approacssh. Negligible matrix effects allow accurate quantitative information. The purpose of this research was to evaluate the main aspects concerning the interfacing process. These fundamental studies were necessary to understand the mechanism of LEI in details, and improve the interfacing process, especially regarding robustness and sensitivity. Hardware components were installed to prevent analytes precipitation, reduce thermal decomposition of sensitive compounds, and to stabilize the nano-flow delivery with different mobile-phase compositions. Particular attention was devoted to insulating the heated vaporization area from the LC part of the system. Experiments were performed to optimize the interface inner capillary dimensions, and other operative parameters, including temperature, gas and liquid flow rates. Test compounds of environmental interest were selected based on molecular weight, thermal stability, volatility, and polarity. Robustness was evaluated with a set of replicated injections and calibration experiments using a soil matrix as a test sample. MRM detection limits in the low-picogram range were obtained for five pesticides belonging to different classes in a soil sample. High-quality electron ionization mass spectra of a mixture of pesticides were also obtained.

New bioactive C15 acetogenins from the red alga Laurencia obtusa

Background and Objective: With regard to the uniqueness of the red algae of the genus Laurencia as the source of C15-acetogenins, along with the diversity of biological applications; the acetogenin content of the Red Sea Laurencia obtusa was investigated. Materials and Methods: Fractionation and purification of the CH2Cl2/MeOH extract were carried out by applying several chromatographic techniques, including column and preparative thin-layer chromatography; followed by a series of 1H nuclear magnetic resonance measurements to give rise of some interesting notes. Toxicity to Artemia salina was evaluated. The apoptosis induced by these two compounds was demonstrated by DNA fragmentation assay and microscopic observation. Results: A new rare chloroallene-based C15 acetogenin, laurentusenin (1) along with a new furan ring containing C15 acetogenin, laurenfuresenin (2), were isolated from the red alga L. obtusa. Comparing 1D and 2D NMR, MS, ultraviolet and infrared radiation spectral data for the newly isolated compounds with the reported bromoallene containing acetogenins spectral data was played the crucial role for characterization of their chemical structures. 1 and 2 exhibited bare toxicity (LD50 >12 mM) in test organism, A. salina and induced apoptotic death confirmed by DNA fragmentation and microscopic investigations. Conclusion: The isolated metabolite 1 showed unusual substituted allene side chain, while 2 inserted furan ring as a new acetogenin nucleus. Both compounds may play a role in apoptosis induction and initiation and propagation of inflammatory responses. Abbreviations used: NMR: Nuclear magnetic resonance; MS: Mass spectrometry; UV: Ultraviolet spectroscopy; IR: infrared radiation; EIMS: Electron ionization mass spectra; TLC: Thin-layer chromatography; PPP: Platelet poor plasma; PRPDS: platelet-rich plasma derived serum. DEPT: Destortionless Enhancement by Polarization Transfer; NOESY: Nuclear Overhauser Effect Spectroscopy; HSQC: Heteronuclear Single Quantum Coherence; HMBC: Heteronuclear Multiple-quantum Correlation; 1H-1H COSY: Correlation Spectroscopy.

Spectroscopic differentiation and chromatographic separation of regioisomeric indole aldehydes: Synthetic cannabinoids precursors

The compounds in this study are the six regioisomeric 2-, 3-, 4-, 5-, 6- and 7-formyl indoles and the corresponding six regioisomeric N-n-pentylindole aldehydes. These compounds can serve as precursor chemicals and synthetic intermediates for a number of synthetic cannabinoid drugs. These two sets (the six regioisomeric indole aldehydes as well as the six regioisomeric pentylindole aldehydes) each have identical elemental compositions and differ in the position of attachment of the aldehyde group on the indole ring.The electron ionization mass spectra for the indole aldehydes were essentially identical. However, the vapor phase infrared spectra showed differences in the absorption frequencies for the NH and carbonyl groups based on intramolecular interactions. The associated NH absorption band occurs as low as 3467 cm−1 while the free band is as high as 3517 cm−1. The aldehyde carbonyl band for the indole aldehydes varies from 1713 cm−1 to 1686 cm−1. Substitution of the aldehyde group on the pyrrole ring for the N-n-pentylindole aldehydes yields lower carbonyl absorption bands. The EI mass spectra for the pentylindole aldehydes are identical with little information for differentiation among these six regioisomeric compounds. The six compounds were separated on a capillary column using gas chromatography and the elution order appears to be related to the steric crowding of the indole ring substituents.

Mass Spectrometry Study of New Polyamine Derivatives of Caffeine

The mass spectrometric fragmentations of ten new 8-alkylaminocaffeine derivatives were investigated. The fragmentation pathways of new polyamine derivatives of caffeine on the basis of low and high-resolution electron ionization (EI) mass spectra were discussed. In the case of new compounds, classical fragmentation of purine skeleton related to the elimination of a neutral molecule CH3N(1)C(2)O from a molecular ion was not observed. Nevertheless, new, interesting fragmentation of described caffeine derivatives was observed. Moreover, heats of formation of odd-electron ions of 8-alkylaminocaffeine derivatives were calculated.

Characterization of Dialkyl Phosphites by Gas Chromatography–Mass Spectrometry

The homologous series of dialkyl phosphonates (CnH2n + 1O)2PH=O] (2 ≤ n ≤ 9) (dialkyl phosphites is their commonly used trivial name) was characterized by electron ionization mass spectra and retention indices (RIs) on an RTX-5 standard nonpolar stationary phase. It was established that, in the presence of even one chiral center in the alkyl fragments (for example, in sec-alkanol esters), dialkyl phosphonates were detected in the form of several chromatographic signals due to diastereomers with differences in the retention indices from 4 to 21. The four-coordinated phosphorus atom is the second chiral center. The homologous increments of the retention indices of di-n-alkyl phosphonates (iRI ± sRI = 29 ± 9) and esters having one (–4 ± 10) and two (–61 ± 14) branching points in the carbon skeletons of alkyl fragments were evaluated. These values, which were calculated based on data for a limited number of homologues, make it possible to characterize any compounds from the test series. It was found that the relationship М ≈ 0.14(RI – iRI) + y makes it possible to uniquely determine the molecular weights of analytes according to chromatographic data under the condition of rounding the results to the nearest value of M comparable with y = 12 to the modulus 14 [М ≡ 12(mod14)].

Group Identification of O-Alkyl Alkylphosphonothionofluoridates by Electron Ionization Mass Spectra Using Generalized Spectral Images of Taxonomic Groups

A method is proposed for the group identification of poorly studied highly toxic O-alkyl alkylphosphonothionofluoridates by electron ionization mass spectra. The method is based on the use of generalized spectral images of four taxonomic groups of this class, subjected to control under the Chemical Weapon Convention. The generalized spectral images were obtained by analyzing the revealed regularities of the fragmentation of these compounds. An advantage of the proposed method is that the assignment of a test substance to one of the class groups and to a class as a whole is a rapid automated standard procedure used in the NIST information retrieval system.

An Improved Procedure for the Gas Chromatography–Tandem Mass Spectrometry Detection of the Globin Adduct of Sulfur Mustard

Features of the electron and chemical ionization mass spectra of derivatives of N-[2-[(hydroxyethyl)thio]ethyl]-DL-valine (НЕТЕ-Val)—a biomarker of sulfur mustard—recorded by GC–MS and GC–MS/MS are studied. The retention indices of the studied derivatives were measured. An optimized procedure of the GC–MS/MS (MRM mode) identification of НЕТЕ-Val was tested in the analysis of donor blood samples in vitro exposed to sulfur mustard. The linear range of the detector was from 10 to 100 ng mL–¹, and the limit of detection for sulfur mustard was 10 ng mL–¹.

Electron Ionization Mass Spectra of Trimethylsilyl–Pentafluoropropionyl and Trimethylsilyl–Heptafluorobutyryl Derivatives of β-Adrenoreceptor Modulators

The paper presents proposals for the mass spectrometric determination of β-adrenoreceptor modulators by bifunctional derivatization with N-methyl-N-(trimethylsilyl)-trifluoroacetamide followed by acylation with pentafluoropropionic or heptafluorobutyric anhydrides with a description of the derivatives obtained.

Gas Chromatography-Mass Spectrometry (GC-MS) and Gas Chromatography-Infrared (GC-IR) Analyses of the Chloro-1- n-pentyl-3-(1-naphthoyl)-Indoles: Regioisomeric Cannabinoids.

The analytical differentiation of the indole ring regioisomeric chloro-1- n-pentyl-3-(1-naphthoyl)-indoles is described in this report. The regioisomeric chloroindole precursor compounds, N- n-pentyl chloroindole synthetic intermediates, and the target chloro-substituted naphthoylindoles showed the equivalent gas chromatographic elution order based on the position of chlorine substitution on the indole ring. The regioisomeric chloro-1- n-pentyl-3-(1-naphthoyl)-indoles yield electron ionization mass spectra having equivalent major fragments resulting from cleavage of the groups attached to the central indole nucleus. Fragment ions occur at m/z 127 and 155 for the naphthyl and naphthoyl cations common to all indoles having the naphthoyl group substituted at the indole-3 position. Fragments resulting from the loss of the naphthoyl and/or n-pentyl groups from the molecular radical cation yield the cations at m/z 318, 304, 248, and 178. The characteristic (M-17)+ fragment ion at m/z 358 resulting from the loss of OH radical is significant in the mass spectra of all these compounds with 1-naphthoyl groups substituted at the indole-3 position. The vapor phase infrared spectra provide a number of characteristic absorption bands to identify the individual isomers.

Mass spectral studies of N-oxides of chemical weapons convention-related aminoethanols by gas chromatography/mass spectrometry after silylation.

N-Alkylaminoethanols, N,N'-dialkylaminoethanols, and triethanolamine are the hydrolyzed products or precursors of V-agents/nitrogen mustards. These compounds are prone to undergo oxidation in environmental matrices. Detection of the oxidized products provides a clue for the presence of parent amine compounds and it is an important task in the verification process of chemical weapons convention. Gas chromatography/mass spectrometry is the technique of choice for the detection of most of the chemical warfare agents; however, it is ideal to develop gas chromatography/mass spectrometry techniques for all the possible degradation products of chemical warfare agents as well. In general, the N-oxides of amines are expected to be thermally unstable; hence, the gas chromatography/mass spectrometry analysis of the N-oxides of triethanolamine, N-alkyldiethanolamines and N,N'-dialkylaminoethanols is not explored. In this study, the N-oxides of chemical weapons convention-related aminoethanols (13 compounds) were successfully silylated and then analyzed by gas chromatography/mass spectrometry under electron ionization and chemical ionization techniques. The electron ionization mass spectra showed abundant molecular ions and structure indicative fragment ions including [M-(O+CH2CH2OH)]+. The alkyl groups attached to nitrogen resulted in structure-specific fragment ions that enable differentiation of isomeric compounds. The methane/chemical ionization spectra showed considerably abundant [M+H]+ (>10%) and the expected adduct ions. The retention indices of all the compounds were calculated using Van den Dool's formula. The gas chromatography/mass spectrometry data together with retention index values could be used for unambiguous identification of the N-oxides of aminoethanols during off-site analysis or proficiency tests.

Identification of halogenated polycyclic aromatic hydrocarbons in biological samples from Alberta Oil-Sands Region

Halogenated polycyclic aromatic hydrocarbons (HPAHs) were identified in biological samples from the Alberta Oil-Sands Region (AOSR) using gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GC-HRTOF-MS) at a resolving power of 25,000. Knowledge of the electron ionization (EI) fragmentation behavior of individual HPAH isomers, achieved by injecting authentic standards in full-scan MS mode, was paramount in identifying a suite of HPAHs in samples from the AOSR. Confirmation of compounds in biological samples was based on the measured mass accuracy (±3 ppm) of 2 characteristic ions prominent in the EI mass spectra of each compound. Numerous compounds were detected in the high resolution total ion chromatogram in liver extracts of 4 biological species from the AOSR: river otter (Lontra Canadensis), northern pike (Esox lucius), lake whitefish (Coregonus clupeaformis) and snails (Gastropod sp.) many of which remain unidentified. Careful examination of the high-resolution accurate mass data suggests that dichloro-anthracene/phenanthrene, bromo-anthracene/phenanthrene and dibromo-fluorene were present in the biological samples. Lipid corrected concentrations of dichloro-PAHs were estimated to be 16.3 ± 11.4 (n = 4) and 5.5 (n = 1) ng/g in lake whitefish and river otter, respectively. Concentrations of mono-bromo-PAHs were an order of magnitude greater in snails (170.5 ng/g) than in northern pike (12.5 ng/g) while concentrations of dibromo-PAHs were 4 times greater in snails than in northern pike. The detection of these compounds in biota implies that these compounds are bioaccumulative. The liver-based biomagnification factor of the dichloro-PAH congener in the river otter/lake whitefish feeding relationship is much smaller than 1 implying that this compound does not biomagnify.

Elucidating the mass spectrum of the retronecine alkaloid using DFT calculations.

Pyrrolizidine alkaloids are natural molecules playing important roles in different biochemical processes in nature and in humans. In this work, the electron ionization mass spectrum of retronecine, an alkaloid molecule found in plants, was investigated computationally. Its mass spectrum can be characterized by three main fragment ions having the following m/z ratios: 111, 94, and 80. In order to rationalize the mass spectrum, minima and transition state geometries were computed using density functional theory. It was showed that the dissociation process includes an aromatization of the originally five-membered ring of retronecine converted into a six-membered ring compound. A fragmentation pathway mechanism involving dissociation activation barriers that are easily overcome by the initial ionization energy was found. From the computed quantum chemical geometric, atomic charges, and energetic parameters, the abundance of each ion in the mass spectrum of retronecine was discussed.

GC-MS and GC-IR analysis of regioisomeric cannabinoids related to 1-(5-fluoropentyl)-3-(1-naphthoyl)-indole

The compounds in this study are the regioisomeric 2-, 3-, 4-, 5-, 6- and 7-(1-naphthoyl) substituted 1-(5-fluoropentyl)-indoles and the 3-(1-naphthoyl) substituted isomer in this series is also known as AM-2201. These compounds are structurally similar to JWH-018 except for the additional fluorine at the terminal end of the n-pentyl side-chain. These six regioisomeric compounds have the identical elemental composition (C24H22FNO) and differ in the position of attachment of the 1-napthoyl group on the indole ring. The electron ionization mass spectra showed similar major fragment ions with a molecular radical cation of significant abundance at m/z 359. The six compounds have similar fragment ions at m/z 127 and 155 for the naphthyl and naphthoyl cations. There is a prominent fragment ion at m/z 342 [M−17]+ in the EI-MS of 1-(5-fluoropentyl)-3-, 4-, 5- and 6-(1-naphthoyl)-indoles due to the loss of the hydroxyl group and this ion is most prominent in the 3-(1-naphthoyl) substituted isomer (AM-2201).The six compounds were separated using gas chromatography on a capillary column containing a trifluoropropylmethyl polysiloxane (Rtx-200) stationary phase. The elution order appears to be related to the steric crowding of the indole ring substituents. The 7- and 2-(1-naphthoyl) substituted isomers eluted first due to the possibility for maximum interactions between the naphthyol and alkyl side-chains.The vapor phase infrared spectra differentiate among these six compounds based on the position of the 1-naphthoyl group on the indole ring. The vapor phase spectra for these compounds are compared to the non-fluorinated analogues, JWH-018 and its regioisomeric equivalents.

GC-MS and GC-IR Analyses of the Methoxy-1-n-pentyl-3-(1-naphthoyl)-indoles: Regioisomeric Designer Cannabinoids.

The indole ring regioisomeric methoxy-1-n-pentyl-3-(1-naphthoyl)-indoles represent indole ring-substituted analogs of the synthetic cannabinoid JWH-018. The electron ionization mass spectra show equivalent regioisomeric major fragments resulting from cleavage of the groups attached to the central indole nucleus. The characteristic (M-17)+ fragment ion at m/z 354 resulting from the loss of OH group is significant in the mass spectra of all four compounds. Fragmentation of the naphthoyl and/or pentyl groups yields the cations at m/z 314, 300, 244 and 216. The vapor-phase infrared spectra provide a number of characteristic absorption bands to identify the individual isomers. Gas chromatographic separations on a capillary column containing a film of trifluoropropylmethyl polysiloxane (Rtx-200) provided excellent resolution of these compounds, their precursor indoles and intermediate pentylindoles. The elution order appears related to the degree of crowding of indole ring substituents.

Electron interactions with Bis(pentamethylcyclopentadienyl) titanium(IV) dichloride and difluoride

We present a combined experimental and theoretical study of the interaction of electrons with Bis(pentamethylcyclopentadienyl)titanium(IV) dichloride (Cp2*TiCl2) and difluoride (Cp2*TiF2). We report the experimental measurements of partial cross sections for the dissociative electron attachment (DEA) and the electron ionization (EI) mass spectra of isolated molecules. Estimates of the absolute cross sections are done on the basis of cross-calibration in the case of DEA and on the basis of binary-encounter-Bethe calculation in the case of EI. EI of both molecules is similar, concerning cross section amplitude and fragmentation pattern. DEA is different: DEA to Cp2*TiF2 primarily results in the formation of stable parent anion, while DEA to Cp2*TiCl2 results in the strong fragmentation, primarily into Cl− anion. Possible use of the molecules as the model species for studies of DEA efficiency in postirradiation chemistry is discussed.

Mass spectral differentiation of positional isomers using multivariate statistics

Mass spectral analysis is considered to be a confirmatory method of analysis for the purpose of identifying controlled substances. However, the spectra of positional isomers are generally too visually similar to allow for differentiation. This study of fluoromethcathinone (FMC) and fluorofentanyl has shown that multivariate statistical analysis offers a feasible means of differentiating between electron ionization mass spectra of positional isomers. Three positional isomers of each compound (2-FMC, 3-FMC, 4-FMC, meta-fluorofentanyl, ortho-fluorofentanyl, and para-fluorofentanyl) were analyzed twice daily using gas chromatography/electron ionization mass spectrometry (GC/EI-MS) on six separate instruments over five days. This resulted in 60 mass spectra collected for each positional isomer. Principal component analysis (PCA) followed by linear discriminant analysis (LDA) was performed and successful differentiation of positional isomers was achieved. Leave-One-Sample-Out Cross Validation showed no errors for either group of isomers. Nineteen blind study samples were analyzed for each group of positional isomers with no misclassifications. Furthermore, data from previous case samples was analyzed using this method and in all cases the samples were properly attributed to the correct positional isomer. In addition to visual inspection of the LDA plots, objective classifications were conducted using the resulting posterior probabilities generated when LDA was performed. The results indicate multivariate statistical analysis is a promising addition to the analytical scheme of the identification of positional isomers. This would allow for higher confidence in the final identification of a compound without the need for additional instrumental analysis, saving laboratories both time and money.

Discrimination of synthetic cathinones by GC–MS and GC–MS/MS using cold electron ionization

Gas chromatography–mass spectrometry is currently among the methods of choice for the analysis of synthetic cathinones. However, these analytes are extremely labile, and classical electron ionization (EI) results in excessive and relatively uninformative fragmentation, yielding little to no molecular ions. Cold EI reduces the internal energy of the analytes by expansion of supersonic molecular beams prior to their ionization, leading to improved molecular ion information. In this study, classical and cold EI were compared for the analysis of synthetic cathinones. We demonstrated that cold electron ionization produced enhanced molecular ion intensity for most of the bath salts considered, as well as more informative fragmentation. Principal component analysis showed that cold EI mass spectra are more discriminative than those obtained by classical EI. MS/MS can offer improved confidence in synthetic cathinone identification even in cases where the relative intensity of the molecular ion is very low in MS spectra.

The structure identification of a diphenhydramine-related impurity in methamphetamine.

Some methamphetamine (MA) crystals contain pharmaceutical impurities resulting from the co-ingredients of medicines used for extracting ephedrine/pseudoephedrine. These pharmaceutical impurities and their related byproducts can reflect the trends in precursor chemicals and manufacturing sources. In this research, 1 pharmaceutical-impurity-related byproduct was detected in several seized MA samples synthesized by I/P (Nagai, Moscow, or Hypo) method. Its structure was postulated through the analysis of fragment ions in electron ionization (EI) mass spectrum. The impurity was further synthesized and analyzed using electrospray ionization-collision-induced dissociation (ESI-CID) mass spectrum and nuclear magnetic resonance (NMR), and finally determined to be N1 ,N1 ,N2 -trimethyl-N2 -(1-phenylpropan-2-yl)ethane-1,2-diamine. The impurity was inferred to be generated by the reaction of MA and the breakdown of diphenhydramine, a co-ingredient of medicines used for extracting ephedrine/pseudoephedrine. Simulation MA synthetic experiments via Nagai, Moscow, and Hypo methods using ephedrine and diphenhydramine as starting materials were performed to prove our presumption. The presence of the impurity indicates that these MA samples were manufactured from pharmaceutical containing ephedrine/pseudoephedrine and diphenhydramine.

Toxicities of Eucalyptus dives Oil, 3-Carvomenthenone, and Its Analogues against Stored-Product Insects

The insecticidal toxicities of essential oils and other active components extracted from Eucalyptus dives leaves (as well as structural analogues) were studied against stored-product insects, Plodia interpunctella and Tribolium castaneum. 3-Carvomenthenone was purified from E. dives oil, and the structures were elucidated by electron ionization mass spectra, 1H-nuclear magnetic resonance (NMR), 13C-NMR, heteronuclear multiple quantum coherence, 1H-1H correlation spectroscopy, and distortionless enhancement by polarization transfer NMR. Using the fumigant method against P. interpunctella larvae and adults, cyclohexenone exhibited the strongest toxicity (50% lethal dose [LD50] against larvae and adults, 2.45 and 3.63 μg/cm3), followed by methylcyclohexenone (2.95 and 4.24 μg/cm3), seudenone (3.02 and 4.44 μg/cm3), and 3-carvomenthenone (52.4 and 68.7 μg/cm3). Using the contact method, cyclohexenone (LD50 against larvae and adults, 17.25 and 19.35 μg/cm2) exhibited the most potent toxicities against T. castaneum larvae and adults, followed by methylcyclohexenone, seudenone, and 3-carvomenthenone. No functional radical on the backbone (2-cyclohexen-1-one) was more toxic than other chemicals. Structure-activity relationships between 3-carvomenthenone analogues and toxicities indicated that the toxicity of 3-carvomenthenone, cyclohexenone, methylcyclohexenone, and seudenone might be conferred through the dermal organs of T. castaneum and P. interpunctella. This study indicates that E. dives oil, 3-carvomenthenone, cyclohexenone, methylcyclohexenone, and seudenone have potential as natural agents to control stored-product insects.