Ammonia Chemical Ionization Mass Research Articles

ChemInform Abstract: Optimization of Pyrolysis-Desorption Chemical Ionization Mass Spectrometry and Tandem Mass Spectrometry of Polysaccharides.

The operating conditions for pyrolysis–desorption ammonia chemical ionization mass spectrometry and tandem mass spectrometry have been optimized and the technique evaluated for the production and analysis of structurally-informative pyrolytic fragmentation ions corresponding to intact anhydrohexose oligosaccharides, using amylose as the model polysaccharide. Among the various parameters examined it was found that the nature of the solvent used to adhere the sample to the emitter coil and the configuration of the emitter and the rate at which it is heated all play important roles in determining the efficiency of the pyrolytic process and the production of high mass fragment ions. Adjustment of reagent gas pressure together with source temperature also influence the chemical integrity of high mass oligomeric pyrolysis products. Under optimal operating conditions using ammonia reagent gas, the analyses of cellulose, laminarin, agars, and chitin gave relatively abundant ions corresponding to ammonium (or prot...

Characterization of Heteroatoms in Residue Fluid Catalytic Cracking (RFCC) Diesel by Gas Chromatography and Mass Spectrometry

Nitrogen-, sulfur-, and oxygen-containing hydrocarbons in a residue fluid catalytic cracking (RFCC)-derived diesel were characterized by a gas chromatograph equipped with a pulsed flame photometric detector and an electron impact, ammonia chemical ionization mass spectrometer. Caustic and acid extractions on RFCC diesel were performed to isolate the phenolic and basic nitrogen compounds, respectively. The fraction of RFCC diesel that contained the basic nitrogen compounds was reacted with acetic anhydride to allow for chromatographic separation of amino-aromatic compounds from the rest of the non-reactive basic nitrogen compounds. The majority of basic nitrogen compounds were anilines, as expected. Non-basic nitrogen compounds in RFCC diesel were alkyl indoles and alkyl carbazoles. Double-ring and poly-aromatic amines were identified in RFCC diesel by the acetylation reaction. The majority of sulfur compounds in RFCC diesel were alkyl benzothiophenes and dibenzothiophenes, after being isolated by Pd2+ ligand-exchange chromatography. Dihydrobenzohiophenes and dihydronaphthanthiophenes, despite a low concentration, were also identified in the subfractions. The majority of oxygen compounds in RFCC diesel were phenolic compounds. In addition to alkylphenols, bicyclic and polycyclic phenols were identified and characterized in the acidic fraction.

Development and validation of a sensitive gas chromatography–ammonia chemical ionization mass spectrometry method for the determination of tabun enantiomers in hemolysed blood and plasma of different species

The aim of this study was to develop and validate a fast, sensitive and easily applicable GC–MS assay for the chiral quantification of the highly toxic organophosphorus compound tabun (O-ethyl-N,N-dimethylphosphoramidocyanidate, GA) in hemolysed swine blood for further use in toxicokinetic and toxicodynamic studies. These requirements were fulfilled best by a GC–MS assay with positive chemical ionization with ammonia (GC–PCI-MS). Separation was carried out on a β-cyclodextrin capillary column (Supelco BetaDex ® 225) after reversed phase (C18) solid-phase extraction. The limit of detection was 1 pg/ml for each enantiomer (approximately 500 fg on column) and the limit of quantification 5 pg/ml. The GC–PCI-MS method was applied for the quantification of tabun enantiomers in spiked swine blood after hemolysis and in spiked plasma of different species including humans.

Validation and Application of a GC-MS Method for Determining Soman Concentration in Rat Plasma Following Low-Level Vapor Exposure

A method for determining the chemical warfare agent soman (GD) in rat plasma has been validated and applied to low-level inhalation exposure studies currently being conducted. This method utilizes a fluoride ion-based regeneration assay with isotope dilution followed by large volume injection gas chromatography with ammonia chemical ionization mass spectrometric detection. Following sample preparation by solid phase extraction, chromatographic separation was achieved using a 14% cyanopropylphenyl/86% dimethyl polysiloxane capillary column with a total run time of 18.16 min. Soman and the deuterated isotope ((2)H(4)-soman) internal standard were detected using the selected ion monitoring mode and quantitated using the ammonia adduction ratio of m/z ions 200/204. A reproducible linear relationship was obtained for the quantitative concentration range of 10 pg on-column to 1000 pg on-column (r(2) = 0.9995) for standards in ethyl acetate with a detection limit of 5.65 pg on-column, and an average recovery of 93% in plasma. This sensitive method was successfully applied to the analysis of soman in rat plasma immediately post-exposure, resulting in the construction of dose-response plots.

In vivo biotransformation of metoprolol in the horse and on-column esterification of the aminocarboxylic acid metabolite by alcohols during solid phase extraction using mixed mode columns

The in vivo biotransformation of metoprolol tartrate in the thoroughbred racehorse was studied after administration of a single oral dose. Metoprolol and its basic and bifunctional phase I metabolites were isolated from urine and plasma using mixed mode solid phase extraction (SPE) cartridges. The isolates were derivatised as trimethylsilyl ethers and analysed by capillary column gas chromatography—positive ion electron ionisation and ammonia chemical ionisation mass spectrometry. Metabolism was primarily confined to the oxidative transformations of the p-(2-methoxy)ethyl substituent. Metoprolol and five phase I metabolites were detected in horse urine. In common with man, rat and dog, the zwitterionic compound (±)-4-(2-hydroxy-3-isopropylaminopropoxy)-phenylacetic acid (H117/04), was the principle metabolite in the horse. This compound was readily isolated from both plasma and urine samples by SPE and, in addition, an unusual on-column esterification of the carboxylic acid moiety by alcohols was observed. Metoprolol and the major aliphatic acid metabolite were detected for about 10 and 40 h, respectively in unhydrolysed urine. After enzymatic hydrolysis, the detection period increased to 15 and 60 h, respectively indicating some phase II metabolism of metoprolol and its metabolites in the horse.

Analytical mass spectrometry of artists’ acrylic emulsion paints by direct temperature resolved mass spectrometry and laser desorption ionisation mass spectrometry

Direct temperature resolved mass spectrometry (MS) is a microanalytical technique to analyse modern paints by thermal separation and ionisation of organic pigments and polymeric fractions from a platinum/rhodium filament inside the ionisation chamber of the mass spectrometer. Most organic pigments in modern paints are desorbed at lower temperatures. Ethyl acrylate/methylmethacrylate or butyl acrylate/methylmethacrylate copolymers used in acrylic emulsion paints produce mono and oligomeric subunits released from the copolymers at high temperature by pyrolysis. Characteristic low voltage electron ionisation and ammonia chemical ionisation (CI) mass spectra of these copolymers facilitate their identification. DTMS of three different commercial acrylic emulsion paints showed low and high temperature events that could be related to the presence of organic pigments and the acrylic copolymers. Polyethylene glycols with molecular weight up to 2000 Da were identified as additives under ammonia CI conditions. The azo pigments PY3, PY73 and PY74, and the phthalocyanine pigment PG7 reported show molecular ions and a few characteristic fragment ions under direct temperature resolved mass spectrometry (DTMS) analytical conditions. Yellow azo pigments were identified under DTMSMS conditions by their high energy collisionally induced fragment patterns of their parent ions. Laser desorption ionisation mass spectrometry (LDIMS) using a nitrogen laser (337 nm) of an acrylic emulsion paint with four different organic pigments produced radical cations, protonated or sodiated ions of the pigments. The amide bond in the azo pigment PY3 was photolytically cleaved and produced a specific fragment ion. The trace additive polyethylene glycol was observed preferentially while the acrylic copolymers were transparent.

A retrospective view of mass spectrometry and natural products—sixty years of progress, with a focus on contributions by R. Graham Cooks

Modern mass spectrometry as used by chemists has prospered for the past sixty years. During the first decade of this period, the primary compounds studied were from petroleum, although other organic compounds soon attracted interest. By the mid nineteen fifties, mass spectra were being recorded on thousands of compounds each year. Most of this activity was in industrial laboratories, although by 1960 the academic world had realized the potential of the technique. This retrospective, reviewing the past sixty years, is divided into four quarters. The first two quarters cover the thirty-year period to 1970, by the end of which R. Graham Cooks had begun to plant firm roots into mass spectrometry. The major feature of the third quarter is the development by Cooks and his students of tandem mass spectrometry using isobutane or ammonia chemical ionization mass spectrometry coupled to the mass-analyzed ion kinetic energy spectroscopy (MIKES) technique for the direct, rapid, and efficient analysis of complex biological matrices. A milestone in the work was the direct introduction of plant material into the mass spectrometry (MS) source. The fourth quarter of the review covers an explosive growth in the breadth of mass spectrometry. Work in the Cooks laboratory was focused on the application of a series of ion generation and sample introduction techniques, such as desorption chemical ionization, surface-induced dissociation, secondary ion mass spectrometry, and membrane introduction mass spectrometry, to analyze increasingly complex biological matrices. In contrast to the earlier MIKES technique on a sector spectrometer, tandem MS became more common using a triple quadrupole spectrometer, with the natural products being studied ranging in complexity from ethanol to proteins and DNA.

Stereochemical effects enhanced by using selective “self-ionization” under electron ionization conditions in a quadrupole ion trap mass spectrometer

From a previous study on the reactivity of the cis and trans (4-hydroxy-4-methyl-cyclohexyl)-benzoates (Mw = 234) under ammonia chemical ionization conditions in high pressure source, it was demonstrated that competitive decompositions, have specific orientations. In particular, highly stereospecific benzoic acid loss from the trans isomer takes place, suggesting that protonation by NH 4 + regioselectively occurred at the benzoate site rather than at the hydroxyl group. From the cis epimer elimination of water was only observed. This behavior could be explained by (1) possible proton transfer to both the functional groups and (2) decomposition occurring via water loss due to a higher rate constant compared with that of the benzoic acid loss (PA C 6H 5 COOH > PA H 2O ), which is not observed. These epimers are now studied under low pressure chemical ionization (CI) and electron impact (EI) conditions by using an ion trap mass spectrometer. Epimer differentiation from the stereospecific benzoic acid loss can be achieved independently of the gas-phase reagent used for chemical ionization, even if quasimolecular ions are entirely decomposed (i.e. in low pressure isobutane CI and methane CI). More spectacular differentiation is displayed in the ammonia CI mass spectra of epimers. Among the various quasimolecular species, the product [MNH 4–H 2O] + ions, termed substituted ions, usually containing a covalent C–NH 3 + bond are herein in fact a noncovalent form similar to the ammonia solvating protonated(4-hydroxy-4-methyl-cyclohexyl)-benzoate structure, as shown by deuterium labeling. Other product ions such as C 7H 11NH 3 + and {NH 3, C 6H 5COOH 2 +} are detected in contrast to those observed under high pressure source conditions. Collision induced dissociation spectra of the adduct MNH 4 + ions in addition to those of protonated molecules are investigated to obtain information about the location of ammonium (or proton) attachment. It appears for the trans isomer, a regioselective approach to the benzoate group, yielding [MH–C 6H 5COOH] +, takes place rather than attack at the OH site resulting into [MH–H 2O] +. This difference is at the origin of the observed stereospecific decomposition, which occurs via anchimeric assistance. Alternatively, these epimers give similar EI mass spectra, masking all the stereochemical effects, which reappear when using a residence time of 80 ms prior to apply the analytical scan. Under such conditions, ion–molecule reactions are enhanced, yielding formation of the epimeric MH + ions. These “ self-ionization” processes are induced through exothermical proton transfers from many EI fragment ions. Competitive decompositions of the product even-electron MH + species provide a direct cis/ trans differentiation. The diagnostic cleavages involved are comparable to those observed under low pressure CI conditions except that the loss of water occurs from both the precursors. The latter loss indicates that protonation is in competition and takes place at either of the basic sites, in contrast with that observed in chemical ionization. Furthermore, the exothermicity of proton transfer is preserved as internal energy of MH + which allows consecutive decompositions. At higher m/z ratio ranges, several adduct species are stereoselectively observed in the self-ionization mass spectrum of the trans epimer. These specific processes provide enhancement of the stereochemical cis/ trans differentiation.

Molecular characterization of microgram amounts of oceanic colloidal organic matter by direct temperature-resolved ammonia chemical ionization mass spectrometry

Marine colloidal organic matter in coastal waters off the coast of the eastern United States (from Georges Bank and the Mid-Atlantic Bight) is characterized by means of direct temperature-resolved mass spectrometry (DT-MS). Chemical ionization (NH 3) appears to be a very appropriate ionization method for this material. The analytical data confirm the presence of a significant polysaccharide fraction consisting of neutral sugars (normal-, deoxy- and methylated aldoses), N-acetyl aminosugars and, possibly, acidic sugars. The methylated and N-acetyl aminosugars are considered as markers for a bacterial contribution. No evidence is found for polysaccharides with large homopolymeric domains, suggesting an origin distinct from the common structural polysaccharides that comprise major polymers in algae and higher plants. The TIC profiles, which express the number of ions produced as a function of the temperature, often show a bimodal distribution. This indicates that the colloidal matter consists of two fractions with different thermal stabilities and probably also different chemical stabilities. Multivariate “mapping” of the DT-MS spectra reveals that the chemical differences between these two fractions show remarkable conformity amongst samples collected at widespread locations. The relative abundance of the two fractions appears to depend on both depth and location. The more thermally stable fraction is relatively abundant in deep water samples and some surface waters of the Mid-Atlantic Bight.

ChemInform Abstract: Determination of the Sugar Linkage Position in Glycosides Using Ammonia Chemical Ionization Mass Spectrometry at Low Gas Pressure.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Determination of the sugar linkage position in glycosides using ammonia chemical ionization mass spectrometry at low gas pressure

Determination of the sugar linkage position in glycosides using ammonia chemical ionization mass spectrometry at low gas pressure

Pyrolysis chemical ionization mass spectrometry of cellulose ethers

AbstractPyrolysis ammonia chemical ionization (PyCI) mass spectrometry was performed on hy‐droxyethyl‐, hydroxypropyl‐,methyl‐, hydroxypropylmethyl‐, and ethylhydroxyethyl cel‐luloses. The mass peaks in the PyCI mass spectra of these cellulose ethers could be assigned to the ions of pyrolytic dissociation products which form via the [2 + 2 + 2] cycloreversion and the Ei elimination pyrolysis pathway. Structural information about the residual amount of nonderivatized cellulose, the relative chain length distributions of the substituents in hydroxyalkyl celluloses, and the end‐capping of hydroxyalkyl substituents by alkyl groups in the mixed cellulose ethers is obtained. Interference of secondary pyrolysis products in the PyCI mass spectra is found to be of minor importance, especially in the lower mass regions. © 1995 John Wiley & Sons, Inc.

Ammonia chemical ionization mass spectrometry of substituted phenylpropanoids and phenylalkyl phenyl ethers

AbstractThe ammonia chemical ionization (NH3/CI) spectra of phenylpropanoids and substituted phenylalkyl phenyl ethers containing α‐hydroxy or α‐carbonyl functional groups are discussed. Fragmentation reactions which occur in the temperature range 180–450°C are examined to model pyrolysis mass spectrometric experiments of lignin. Hydroxycinnamyl alcohols and α‐hydroxy phenylalkyl phenyl ethers show abundant [M + H − H2O]+ elimination ions and to a lesser extent [M + NH4 − H2O]+ substitution ions while hydroxycinnamic acids and α‐carbonyl phenylalkyl phenyl ethers show predominantly [M + H]+ and [M + NH4]+ ions. The interpretation of functional group information is facilitated by using trideuterioammonia (ND3) and [15N] ammonia (15NH3) as reagent gases. Labile hydrogens undergo essentially complete exchange upon ND3/CI and the number of hydroxyl functional groups is readily determined by comparison of the [M + NH4]+ and [M − nH + nD + ND4]+ adduct ions. Incomplete HD exchange is observed for enolizable and aromatic protons.

Assay of zatebradine in plasma by fully automated sample clean-up, capillary gas chromatography and ammonia chemical ionisation mass spectrometry.

A method has been developed for the measurement of zatebradine (UL-FS 49), a heart-rate lowering drug, suitable for the treatment of stable angina pectoris. The method comprises a fully automated liquid-solid extraction using a Zymark Benchmate, a capillary gas chromatography and ammonia chemical ionisation (CI) mass spectrometry using hexadeuterated zatebradine for the internal standard. The assay has a mean between-batch imprecision of 4.9% and a mean inaccuracy of 1.5%. The calibration curve covers the range of 1-30 ng/ml. About 60 samples can be handled per day. The assay has been successfully applied to human pharmacokinetic studies.

Conformation dependence in the chemical ionization mass spectra of 3‐pinanones

AbstractThe conformation of the rigid isomer pair of cis‐ and trans‐3‐pinanones was investigated using methane, isobutane, and ammonia chemical ionization (CI) mass spectrometry as a tool to study the dependence of the mass spectrometric fragmentation patterns. The methane and the isobutane CI mass spectra of the cis and trans isomers were found to be different enough to permit the differentiation of the isomers. Each isomer exhibited distinctive fragmentation paths. The isobutane mass spectra of the cis isomer was dominated by the loss of H2O from the pseudo‐molecular ion, whereas the loss of C2H4O was the predominant fragment for the trans isomer. Molecular modeling and quantum‐chemical computations were used to calculate the conformers of lowest energy for the two isomers. The theoretical calculations were then used to explain the differences observed in the chemical ionization mass spectra.In addition, high resolution mass spectrometry measurements, deuterium labeling experiments and energy calculations of the hypothetical transition states and ionized species were helpful and were used to propose mechanisms for the CI mass spectral fragmentation.

Optimization of pyrolysis–desorption chemical ionization mass spectrometry and tandem mass spectrometry of polysaccharides

The operating conditions for pyrolysis–desorption ammonia chemical ionization mass spectrometry and tandem mass spectrometry have been optimized and the technique evaluated for the production and analysis of structurally-informative pyrolytic fragmentation ions corresponding to intact anhydrohexose oligosaccharides, using amylose as the model polysaccharide. Among the various parameters examined it was found that the nature of the solvent used to adhere the sample to the emitter coil and the configuration of the emitter and the rate at which it is heated all play important roles in determining the efficiency of the pyrolytic process and the production of high mass fragment ions. Adjustment of reagent gas pressure together with source temperature also influence the chemical integrity of high mass oligomeric pyrolysis products. Under optimal operating conditions using ammonia reagent gas, the analyses of cellulose, laminarin, agars, and chitin gave relatively abundant ions corresponding to ammonium (or protonated) adducts of up to anhydrohexose tetrasaccharide. More importantly, the generation of such higher mass fragment ions provided a sustained ionic current of sufficient duration to perform tandem mass spectrometric analyses.

Analysis of cell wall mutants ofSaccharomyces cerevisiaeby pyrolysis mass spectrometry

SUMMARY The main constituents of the cell wall of Saccharomyces cerevisiae, i.e. β-1,3-glucan, β-1,6-glucan and mannan, could be distinguished by pyrolysis ammonia chemical ionization mass spectrometry or Py(CI)MS. Cell walls extracted with alkali, which removes the mannan fraction and part of the glucan from the cell wall, yielded mass spectra that differed clearly from nonextracted cell walls. Multivariate analysis of these spectra showed a shift from ‘mannan-like’ towards ‘glucan-like’ cell walls. Known cell wall mutants, such as mnn9 and kre1, were recognized by this technique. Py(CI)MS in combination with multivariate analysis of the spectra is therefore a useful tool for identifying and characterizing cell wall mutants in yeast.

Triton X‐100 as a reference compound for ammonia high‐resolution chemical ionization mass spectrometry and as a tuning and calibration compound for thermospray

AbstractThe non‐ionic surfactant Triton X‐100, 1‐(1,1,3,3,‐tetramethylbutyl)‐4‐[poly(1,2‐ethanediol)]benzene, has been evaluted as a reference material for positive‐ion high‐resolution ammonia chemical ionization (CI) mass spectrometry and as a tuning and calibration material for positive‐ion thermospray mass spectrometry (TSP). When ammonia is used as the CI reagent gas, Triton‐X‐100 produces evenly spaced ions that 44 u apart. Triton X‐100 cab be volatilized from a solids prove and is routinely used as the reference material for high‐resolution measurements. A reference table has been constructed from the theoretical values for the different masses. Triton X‐100‐Reduced and Triton X‐405‐Reduced were also evaluated as additional reference com‐pounds. As a calibration and tuning compound for TSP, Triton X‐100 affords an envelope of ions centred around m/z 600–700 with ions observed above m/z 1000. Triton X‐100‐Reduced affords a similar envelope although the ions observed are 6 u higher in mass.

Preservation of d-glucose-oligosaccharides in cellulose chars

Microcrystalline cellulose was charred anaerobically at atmospheric pressure and at different temperatures ranging from 190 to 390°C. Temperature-resolved, in-source-filament pyrolysis, ammonia chemical ionisation mass spectrometry (Py-CIMS) of these chars shows ion series of ammonium adduct ions of anhydro-oligosaccharides. These anhydro-oligosaccharides were identified by high-performance liquid chromatography (HPLC) of derivatised, off-line, Curie-point-pyrolysis condensates as β-(1 → 4)-linked glucose oligosaccharides with an 1,6-anhydrosugar terminal at the reducing end. These anhydroglucooligosaccharides were observed in chars even after 2.5 h heating at 270°C. The relative amount of preserved glucose in the chars was determined by acid hydrolysis. Coexistence of two solid phases: (i) residual crystalline cellulose and (ii) a condensed thermostable phase was observed in chars derived from cellulose by heating at 250, 270 and 290°C. It is believed that the formation of this new condensed phase is initiated in the thermally induced, amorphous domains of cellulose. No ether-bonded products of inter- and intra-chain crosslinking reactions were detected in the acid hydrolysates of the chars.

Isotope dilution ammonia chemical ionization mass fragmentographic analysis of urinary 3-O-methylated catecholamine metabolites: Rapid sample clean-up by derivatization and extraction of lyophilized samples

We developed a method for simultaneous quantification of the urinary 3-O-methylated catecholamine metabolites 3-methoxytyramine, normetanephrine and metanephrine by stable isotope-dilution ammonia chemical ionization mass fragmentography. Prepurification of lyophilized samples was done by simultaneous deconjugation and pentafluoropropionylation, followed by extraction and rederivatization. Compared with our previously described method, based on acid hydrolysis, alkaline extraction, derivatization and electron-impact mass fragmentography, the present method was found to be less laborious, more sensitive and presumably more accurate. New urinary excretion values were established for apparently healthy adults. The present prepurification method may prove applicable for profiling of a variety of naturally occurring mono-, di- and polyamines in biological samples.