Ammonia Chemical Ionization Mass Research Articles

Investigation of some 2,3-didehydro amino acids by fast ion bombardment, chemical ionization and mass-selected collision-induced dissociation mass spectrometry

Four 2,3-didehydro amino acids were investigated by fast ion bombardment (FIB) and ammonia chemical ionization (NH3-CI) mass Spectrometry. The protonated molecules formed by the two techniques were mass selected and their respective collision-induced dissociations (CIDs) in the translational energy range 5–200 eV (in the laboratory frame of reference) were investigated. No obvious quantitative differences between the FIB and NH3-CI mass spectra of the (E)- and (Z)-isomers were observed. Different internal excitation of the protonated molecules formed by the two techniques and the role of CID data in clarifying this particular observation are discussed.

Capillary column gas chromatography-ammonia and deuterated ammonia chemical ionization mass spectrometry of sulfur vesicants

Capillary column gas chromatography-ammonia and deuterated ammonia chemical ionization mass spectrometry was found to be a highly specific technique for the detection and identification of three long-chain sulfur vesicants, 2-chloroethyl (2-chloroethoxy)ethyl sulfide, sesquimustard and bis[(2-chloroethylthio)ethyl]ether. All three vesicants exhibited significant (M + NX 4) + (where X = H or 2H) pseudo-molecular ions and structurally significant chemical ionization fragmentation ions during capillary column gas chromatographic-ammonia chemical ionization mass spectrometric analysis. This method was utilized during analysis of contaminated painted panels circulated during the 3rd round robin verification exercise (1991). Chemical ionization data obtained during this exercise complemented the electron impact data obtained for sesquimustard and bis[(2-chloroethylthio)ethyl]ether and the specificity of the technique enabled the confirmation of 2-chloroethyl (2-chloroethyoxy)ethyl sulfide, a compound masked by hydrocarbons in the painted panel extracts.

Positional identification of fluorine in methyl per- O-acetyl-x-deoxy-x-fluoro-α- d-hexopyranosides by electron impact and chemical ionisation mass spectrometry

Fully acetylated methyl x-deoxy-x-fluoro-α- d-glucopyranosides have been studied using electron impact and ammonia chemical ionisation mass spectrometry. Mass analysed metastable ion kinetic energy spectroscopy (MIKE), collisional activation (CID), and accelerated voltage scanning have been used to evaluate complete fragmentation schemes. Characteristic differences in the fragmentation of positional isomers were noted on analysis of the spectra, and these make it possible to determine the location of fluorine in the molecules studied. Collisionally activated fragmentation of [M − OCH 3] + ions, produced by electron impact, provides an alternative method for localisation of the fluorine atoms. To the contrary, MIKE and CID spectra of [M + NH 4] + cluster ions produced by chemical ionisation did not afford such structural information.

Control of the regiospecific synthesis of dialkylpyrrolizidinones and their stereochemical behaviour using gas chromatography/mass spectrometry with chemical ionization

Pyrrolizidine alkaloids were synthesized via the cyclization of an epoxide prepared from a lactam. The regiospecific control of this reaction is demonstrated using gas chromatography/mass spectrometry. Ammonia chemical ionization mass spectrometry permits the determination of the cis–trans stereochemistry of the final products.

An analytical pyrolysis mass spectrometric study of Eucryphia cordifolia wood decayed by white-rot and brown-rot fungi

The decay of Eucryphia cordifolia wood by white-rot and brown-rot fungi was studied with pyrolysis electron impact mass spectrometry (Py(EI)MS) and pyrolysis ammonia chemical ionization mass spectrometry (Py(CI)MS). Py(EI)MS spectra of the wood after decay by the white-rot fungus Ganoderma australe no longer show mass peaks indicative for lignin. The relative abundance of syringyl (dimethoxy) compounds decreases faster than the coniferyl (monomethoxy) compounds. In the same spectra the relative abundance of hexosans increases whereas the relative amount of pentosans remains constant. The presence of oligomeric sugars in the Py(CI)MS spectrum points to a preservation of some polysaccharides. Brown-rot fungal degradation of similar wood samples analysed with Py(EI)MS reveals no mass peaks for polysaccharides, resulting in a spectrum with mass peaks specific for lignin. The Py(EI)MS, revealing lignin dimers, and the Py(CI)MS spectra suggest that the lignin was not modified by the brown-rot fungus. However, the pyrolysis gas chromatography mass spectrometry (PyGCMS) data show an increase in oxygenated lignin pyrolysis products suggesting a molecular change in the lignin due to brown-rotting. In the brown-rotted wood one sugar pyrolysis product (levoglucosan) was observed by Py(CI)MS and PyGCMS suggesting that part of the cellulose polymer system is inaccessible to fungal degradation. Comparing data obtained from 13C cross polarization/magic angle spinning nuclear magnetic resonance (CP/MAS NMR) with data obtained from PyMS reveals that the latter method provides much more structural information.

Detection of sarin and soman in a complex airborne matrix by capillary column ammonia chemical ionization gas chromatography-mass spectrometry and gas chromatography-tandem mass spectrometry

The chemical warefare agents, sarin and soman, were detected and confirmed during full scanning capillary column ammonia chemical ionization mass spectrometry at nanogram levels in spiked extracts of a diesel exhaust environment sampled onto the charcoal of a Canadian C2 respirator canister. The selectivity of ammonia chemical ionization enabled the use of selected ion monitoring and resulted in detection limits of 40 pg and just above 500 pg for sarin and soman respectively in this extract. This diesel exhaust environment, typical of what might be encountered under battlefield conditions, was used to evaluate capillary column ammonia chemical ionization tandem mass spectrometry as a possible verification technology. Chemical interferences were reduced and significantly better detection limits, 15 pg and 80 pg for sarin and soman respectively, were obtained during gas chromatographic-tandem mass spectrometric analysis of these agents in the presence of numerous interfering diesel exhaust and charcoal bed components.

Mechanistic considerations of the protonation and fragmentation of highly functionalized molecules in fast atom bombardment: high resolution mass spectrometry and tandem mass spectrometry analyis of the ions formed by fast atom bombardment of digoxin and related cardiac glycosides

High resolution mass spectrometry and tandem mass spectrometry analyses of the major ions of digoxin formed by fast atom bombardment are presented and discussed to investigate the mechanisms through which fragment ions are formed. Similar cardiac glycosides are also analyzed to provide support for the proposed fragment assignments. Remote site fragmentation with the charge localized on the aglycone portion of the molecule may provide an explanation for the fragment ions observed in these studies because the majority of these ions contain the aglycone portion of the molecule. The results obtained parallel previously reported results from an ammonia chemical ionization mass spectral study of cardiac glycosides.

High-pressure ammonia chemical ionization mass spectrometry and mass spectrometry/mass spectrometry for porphyrin structure determination

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHigh-pressure ammonia chemical ionization mass spectrometry and mass spectrometry/mass spectrometry for porphyrin structure determinationGary J. Van Berkel, Gary L. Glish, Scott A. McLuckey, and Albert A. TuinmanCite this: Energy Fuels 1990, 4, 6, 720–729Publication Date (Print):November 1, 1990Publication History Published online1 May 2002Published inissue 1 November 1990https://doi.org/10.1021/ef00024a018RIGHTS & PERMISSIONSArticle Views121Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Comparative EI, CI and FAB Mass Spectrometry of Dialkyl and Monoalkyl 2-Chloroethylphosphonates

Abstract Comparison is made between electron ionization (EI), methane, isobutane and ammonia chemical ionization (CI) and fast atom bombardment (FAB) mass spectrometry of phosphonates related to 2-chloroethylphosphonic acid

Thermal fragmentation analysis of neutral polysaccharides and the presence of 1,6-anhydrooligosaccharides

Small quantities of pyrolysates were obtained from micro-scale off-line pyrolysis of the neutral polysaccharides: cellulose, amylose, laminaran, nigeran, and a mannan from ivory nut. The pyrolytic fragments were analyzed by desorption chemical ionization – mass spectrometry, trimethylsilyl derivatization – capillary gas chromatography (– ammonia chemical ionization mass spectrometry) and benzoyl derivatization – high pressure liquid chromatography. Intact 1,6-anhydrohexosemonosaccharide, and -disaccharide fragments were identified as major products. By using off-line analytical pyrolysis information on saccharide composition can be obtained from the formation of anhydromonosaccharide products while linkage information is obtainable from distinctive anhydrodisaccharide products. Keywords: pyrolysis, polysaccharides, 1,6-anhydrooligosaccharides, desorption chemical ionization, mass spectrometry, gas chromatography, high pressure liquid chromatography.

Porphyrin pyrrole sequencing: low-energy collision-induced dissociation of (M + 7H)+ generated in-situ during ammonia chemical ionization

A method for pyrrole sequencing of porphyrins, based on high-pressure ammonia chemical ionization mass spectrometry/mass spectrometry (CI-MS/MS), is presented. High-pressure ammonia CI of porphyrins promotes formation of reduced molecular species and tri-, di-, and monopyrrolic fragment ions. The masses and pattern of the pyrrolic fragment ions can be used to determine the pyrrole sequence of the porphyrin. However, because of the complex ion source chemistry involved, these CI mass spectra are difficult to reproduce and are complicated by a plethora of structurally uninformative peaks. As such, pyrrole sequence elucidation based on the CI mass spectrum alone can be arduous, especially in the case of asymmetrically substituted porphyrins. In this paper, the MS/MS daughter ion spectrum of in situ formed (M + 7H){sup +} (i.e., the protonated porphyrinogen) is used to determine the porphyrin pyrrole sequence. Low-energy (30-100 eV) collision-induced dissociation (CID) of (M + 7H){sup +}, using a hybrid mass spectrometer of BEqQ geometry, yields, specific patterns of tri-, di-, and monopyrrolic daughter ions from which the pyrrole sequence of the porphyrin and combined mass of the substituents on the individual pyrroles can be determined. Several porphyrins of different pyrrole sequence are used to demonstrate the CI-MS/MS sequencing method. Themore » capability of the CI-MS/MS method to sequence the pyrroles of porphyrins within a simple mixture of nonisobaric porphyrins is also demonstrated.« less

Comparative Ei, Ci and Fab Mass Spectrometry of Dialkyl and Monoalkyl 2-Chloroethylphosphonates

Abstract Comparison is made between electron ionization (EI), methane, isobutane and ammonia chemical ionization (CI) and fast atom bombardment (FAB) mass spectrometry of phosphonates related to 2-chloroethylphosphonic acid

Trichloromethyl peroxyl radical (Cl 3COO•) mediated oxidation of cholesterol

Oxidation of cholesterol was studied in situ in a Cl 3COO• generating system via a heterogenous reaction of carbon tetrachloride (CCl 4), KO 2 and 18-crown-6 in aprotic solvent (acetonitrile) at 10°C. The reaction mixture without CCl 4 served as a control. Reaction performed with CCl 4 showed the formation of products more polar than cholesterol which were separated by preparative thin layer chromatography (TLC) and purified by normal phase high performance liquid chromatography (HPLC). The data obtained collectively from TLC, HPLC and ammonia chemical ionization mass spectrometry confirmed the formation of 3ß-hydroxy-5-cholesten-7-one, 5-cholesten-3ß, 7ß- and 3ß, 7α-diols and possibly 3ß-hydroxy-5, 6ξ-epoxy-5ξ-cholestan-7-one as Cl 3COO• mediated oxidation products of cholesterol.

Quantification of N-acetylaspartylglutamate, an N-terminal blocked dipeptide neurotransmitter candidate, in brain slice superfusates by gas chromatography—mass spectrometry

N-Acetylaspartylglutamate is a highly promising neurotransmitter candidate. A method for its quantification has been developed that allows to investigate its stimulation-induced release from brain slices. The method is based on ion-exchange prepurification, derivatization with HCl in methanol, separation by capillary gas chromatography and quantification by ammonia chemical ionization mass spectrometry with selected-ion monitoring. Deuterium-labelled N-acetylaspartylglutamate is used as internal standard. The method has been validated, also with respect to possible interfering compounds. A limit of quantification in the low pmol to high fmol range has been achieved, which is clearly sufficient for the intended purpose. A detailed analytical procedure is given, and alternatives for some of the different steps are discussed. Derivatization with diazomethane instead of methanolic HCl turned out to be impracticable. The method may well be applicable to certain other N-terminal blocked di- and tripeptides and to acylated amino acids.

Separation of the reagent ions from the reagent gas in ammonia chemical ionization mass spectrometry

Competitive reactions can occur between neutral ammonia and the [M+H] + and [M+NH 4 ] + species produced in ammonia chemical ionization mass spectrometry. For some compounds, these competitive reactions can result in the loss the [M+H] + and [M+NH 4 ] + species; these undesirable reactions can be avoided by using a Fourier transform mass spectrometer with a dual trapped-ion cell

Quantitative determination of arecoline in plasma by gas chromatography chemical ionization mass spectrometry

A capillary gas chromatography/mass spectrometry (GC/MS) method for the quantitative analysis of arecoline in plasma has been developed for concentrations in the range 1-50 ng ml-1. Hexadeuterated arecoline was utilized as the internal standard. The removal of drug from plasma was accomplished by a two-step liquid/liquid extraction procedure involving a wash step followed by extraction with 5% triethyl amine in ethyl acetate. The GC/MS determinations were carried out with temperature-programmed capillary GC and ammonia chemical ionization mass spectrometry. The [M + H]+ ions of both analyte and internal standard were monitored at m/z 156 and 162, respectively. The method is linear and has sufficient sensitivity, precision, accuracy and selectivity for analysis of drug levels in human plasma.

Covalent interaction of chloroacetic and acetic acids with cholesterol.

The covalent interaction of chloroacetic acid with rat liver lipids was studied in vivo. Rats were given a single oral dose (8.75 mg/kg, 50 microCi) of 1-[14C]chloroacetic acid and sacrificed after 24 hours. Lipids extracted from the livers were separated into neutral lipids and phospholipids by solid-phase extraction using sep-pak silica cartridges. The neutral lipid fraction was further fractionated by preparative thin-layer chromatography followed by reverse-phase high-performance liquid chromatography. The fraction corresponding to the retention time of standard cholesteryl chloroacetate gave a pseudomolecular ion peak at m/z 480/482 ratio: (3:1) on ammonia chemical ionization mass spectrometry, and the fragmentation pattern was found to be similar to that of the standard sample. Under similar conditions, acetic acid resulted in the formation of cholesteryl acetate. The effect of such conjugation reactions on the cell membrane and their contribution to toxicity is presently unknown.

Hepatic fatty acid conjugation of 2-chloroethanol and 2-bromoethanol in rats.

To study the formation of fatty acid conjugates of 2-chloroethanol (2-CE) and 2-bromoethanol (2-BE), rats were administered (by gavage) 50 mg/kg of 2-CE and 2-BE in mineral oil and sacrificed on fifth day of the treatment. Hepatic microsomal lipids were extracted, and the fatty acid esters were separated by preparative thin-layer chromotography. The ester fraction was further purified by reverse-phase, high-performance liquid chromatography and analyzed by ammonia chemical ionization mass spectrometry. Pseudomolecular ions (M + NH4+, base peak) at m/z 336/338, 362/364, and 364/366 in a ratio of 3:1 and 380/382 and 408/410 in a ratio of 1:1 confirmed the in vivo formation of 2-chloroethyl palmitate, 2-chloroethyl oleate, 2-chloroethyl stearate, 2-bromoethyl palmitate, and 2-bromoethyl stearate, respectively. These results demonstrate the formation of fatty acid conjugates of 2-CE and 2-BE in vivo. These fatty acid conjugates may be retained in the body for a longer time and cause toxic manifestations.

Electron impact and isobutane and ammonia chemical ionization mass spectrometry of some tetrahydropyranyl acetals

The electron impact induced fragmentations of 24 tetrahydropyrane ethers of different types of alcohols were studied by exact mass measurement and metastable ion analysis. The most characteristic features of the spectra were associated with the tetrahydropyrane ring, As the size of the molecule increased, the fragmentations with respect to exocyclic oxygen became more important allowing differentiation among the isomeric aliphatic alcohols. Under isobutane chemical ionization, loss of neutral alcohol from [M + H]+ leading to the formation of a tetrahydropyranium ion was dominant for aliphatic alcohol derivatives, whereas loss of 2-hydroxy tetrahydropyrane giving rise to an alkyl ion was dominant for bicyclic alcohol derivatives. Under ammonia chemical ionization, nucleophilic substitution reactions were always most important.

Mass spectra of some acetals

The electron impact (El), methane chemical ionisation (CH4 Cl) and ammonia chemical ionisation (NH3 Cl) mass spectra of five acetals have been obtained. The [graphic omitted] ions dominate the total ion current under El (70 and 14 eV). In the CH4 Cl mode, the [(M+ 1)–CH3OH]+ ions form the base peaks, except for methyl 2-(dimethoxymethyl)-5-(2-hydroxyethyl)-cyclopent-3-en-1-ylacetate, compound (V), which yields [(M+ 1)–2CH3OH]+ as the base peak. The [M+ 1]+ ion is absent from the NH3 Cl mode, but the fragmentation patterns are still complicated. The main fragmentation pathways include fragmentation from the cluster adduct ions, from the charge-transfer products and from the aldehyde, a product from the reversed reaction of the acetal. The difference in energy gained by the molecular ions during the ionisation process leads to this feature.