Methane Chemical Ionization Mass Spectrometry Research Articles

Regio-and Stereochemical Effects in the Chemical Ionization Mass Spectra of Isomeric Bicyclo|3, 2, O| Heptan-2-One Trimethylsiloxy Derivatives1

Isomers of bicyclo |3, 2, O| heptan-2-one trimethylsiloxy derivatives, produced by (π2+π2) photocycloaddition reactions between cyclopent-2-enones and trimethylsiloxy alkenes, have been investigated by methane and isobutane chemical ionization mass spectrometry. Head-to-head and head-to-tail regioisomers and the syn-and anti-epimers in each regioisomeric set can be identified by means of these ionization methods. Prominent fragmentation patterns are discussed.

Electron ionization and methane chemical ionization mass spectrometry study of some 2,2‐disubstituted 1,3‐dioxolanes, 1,3‐dithiolanes, 1,3‐oxathiolanes and 1,3‐dioxanes. Gas‐phase lactone and thiolactone formation

AbstractThe electron ionization and methane chemical ionization mass spectra of some 2,2‐disubstituted 1,3‐dioxolanes, 1,3‐dithiolanes and 1,3‐oxathiolanes were studied. Especially, the effect of the length of the side chain in ring position 2 of these compounds and the ease of formation of possible lactone/thiolactone ion as a fragmentation product were examined. In addition, two 2,2‐disubstituted 1,3‐dioxanes were studied to see the effect of the bigger ring size. The formation of lactone ions was more favorable under methane chemical ionization than under electron ionization conditions. The structures of fragment ions and the ions generated from model compounds were carefully studied using both high‐ and low‐energy collision‐induced dissociation. Also ab initio molecular orbital calculations up to the HF/6–31G** level of theory for protonated 2‐methyl‐2‐propanoic acid ethyl ester of 1,3‐dioxolane, 1,3‐oxathiolane and 1,3‐dithiolane and for two isomeric bicyclic ions were carried out. The theoretical results obtained favor the formation of the lactone ion. Copyright © 2005 John Wiley & Sons, Ltd.

Determination of trifluoroacetylated glycosides by gas chromatography coupled to methane negative chemical ionization mass spectrometry

Gas chromatography coupled to methane chemical ionization mass spectrometry was used for qualitative determination of trifluoroacetylated plant glycosides. The mass spectra obtained exhibited characteristic fragment ions of the sugar moiety and molecular or pseudo-molecular ions. The pattern of these chemical ionization spectra was influenced by source temperature. This method was applied to the structural determination of glycosides from purple passion fruit and muscat wine (Muscat of Frontignan) extracts obtained by adsorption on Amberlite XAD-2.

The identification of the allylic nitrite and nitro derivatives of methyl linoleate and methyl linolenate by negative chemical ionization mass spectroscopy

The autoxidation of polyunsaturated fatty acids is initiated both in vivo and in vitro by nitrogen dioxide. The mechanism of the initiation process is believed to involve both addition reactions and hydrogen atom abstraction reactions, with hydrogen abstraction predominating at low levels of nitrogen dioxide. Therefore low levels of nitrogen dioxide should react with polyunsaturated fatty acids to give allylic derivatives; in an anaerobic system these derivations should be allylic nitro and nitrite compounds. Using negative methane chemical ionization mass spectrometry and other analytical techniques, we have identified these allylic nitrite and nitro compounds from the reactions of low levels of nitrogen dioxide with methyl linoleate and methyl linolenate in the absence of oxygen.

Chlorination of linoleic acid

Aqueous chlorination of linoleic acid gave a mixture of tetrachlorostearic acid, trichlorohydroxystearic acid and dichlorohydroxystearic acid of linoleic acid in relative percentages of 49%, 38% and 13% respectively. Treatment of threo- cis- cis-9,10,12,13-diepoxystearic acid with HCl gave a mixture of tetrahydrofuranyl ethers and dichlorohydrins in relative percentages of 24% and 76%. A separate synthesis of trichlorohydroxystearic acid is described. Products were identified by infrared spectrometry (IR), nuclear magnetic resonance spectroscopy (NMR) and negative methane chemical ionization mass spectrometry (NCl). Chlorohydrins were confirmed by their conversion to epoxides by NaOH.

Electron impact and methane chemical ionization mass spectrometry of trisilanes and trisiloxanes

The electron impact and methane chemical ionization mass spectrometry of fifteen trisilanes and trisiloxanes containing various substituents was studied with the aid of exact mass measurements and metastable ion analyses. Migration reactions of the two kinds of compounds are discussed

A Urinary Cysteine-Halothane Metabolite

SUMMARY An attempt was made in children to identify a urinary halothane—cysteine conjugate which had been described previously in adult patients following administration of halothane. If this conjugate was found it would indicate that a reductive metabolite of halothane binds covalently with the sulphydryl-containing amino acid, cysteine, a reaction which could lead to hepatic injury. The potential halothane—cysteine conjugate, N-acetyl-S-(2-bromo-2-chloro-1, 1-difluoroethyl)-L-cysteine (acetyl BCFEC), was prepared and the identity of the compound established using hydrogen-1 and carbon-13 NMR spectroscopy and methane chemical ionization mass spectrometry. A measurement technique for acetyl BCFEC was developed using HPLC with u.v. detection at 200 nm. In six children after halothane anaesthesia, one child being studied twice, urine was collected for up to 1 week and analysed for acetyl BCFEC. Little or no acetyl BCFEC was detected in any of the 43 urine samples tested, indicating that in children it is not a significant urinary metabolite of halothane.

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

A URINARY CYSTEINE-HALOTHANE METABOLITE: VALIDATION AND MEASUREMENT IN CHILDREN

An attempt was made in children to identify a urinary halothane-cysteine conjugate which had been described previously in adult patients following administration of halothane. If this conjugate was found it would indicate that a reductive metabolite of halothane binds covalently with the sulphydryl-containing amino acid, cysteine, a reaction which could lead to hepatic injury. The potential halothane-cysteine conjugate, N-acetyl-S-(2-bromo-2-chloro-1,1-difluoroethyl)-L-cysteine (acetyl BCFEC), was prepared and the identity of the compound established using hydrogen-1 and carbon-13 NMR spectroscopy and methane chemical ionization mass spectrometry. A measurement technique for acetyl BCFEC was developed using HPLC with u.v. detection at 200 nm. In six children after halothane anaesthesia, one child being studied twice, urine was collected for up to 1 week and analysed for acetyl BCFEC. Little or no acetyl BCFEC was detected in any of the 43 urine samples tested, indicating that in children it is not a significant urinary metabolite of halothane.

Mass spectral characterization of acyloxymethyl phosphates.

A series of organophosphates having one or two acyloxymethyl groups have been characterized by methane chemical ionization mass spectrometry: twelve are model compounds with phenyl and benzyl groups while four are derived from pyrimidine-3'-deoxyriboside-5'-monophosphates. Some are protonated cyclohexyl-ammonium salts. In addition the phenyl and benzyl phosphate spectra exhibit an abundance of fragmentation and rearrangement ions, the majority of which were products of three processes--expulsion of formaldehyde, loss of the acyloxymethyl group with transfer of hydrogen to the phosphate, and fission of the methylene-acyloxy bond. The pyrimidine-3'-deoxyriboside-5'-monophosphate esters give less fragmentation under similar circumstances; prominent ions in their spectra are the protonated molecular ions and losses of one and two molecules of formaldehyde from them and the protonated bases.

Methane chemical ionization mass spectrometry of the pentafluorobenzyl derivatives of abscisic acid, its metabolites and other plant growth regulators

Tetraethyl ammonium hydroxide has been used as a catalyst for the pentafluorobenzylation of abscissic acid and its metabolites, as well as zeatin, gibberellic acid and indole acetic acid. These derivatives, acetylated where necessary, were subjected to methane negative ion chemical ionization mass spectrometry. The spectra were quite simple and are therefore ideally suited for selected ion monitoring at high sensitivity with heavy isotope labelled internal standards. The sensitivity for pentafluorobenzyl abscisate was 20 fg with a signal to noise ratio of greater than 10:1. The other compounds were within an order of magnitude of this. It is thus feasible, at least in principle, to quantify components from all four groups of plant growth regulators from the same tissue.

Occurrence of an unusual amount of an odd-numbered fatty acid in glycosphingolipids from human cataracts.

Human cataractous glycosphingolipids were isolated and purified according to previously established procedures. Fatty acid analyses of the purified glycosphingolipid revealed the presence of a significant amount of an odd-chain fatty acid. This was confirmed by methane (CH4) chemical ionization mass spectrometry, which showed characteristic ions at m/z 397, 425, 437, and 365. These ions facilitated the determination of molecular weight and the assignment of C25:0 (n-pentacosanoic acid) to this fatty acid in question. This may be the first time that such an unusual distribution of a single odd-chain fatty acid has been shown to occur in glycosphingolipid from any tissue.

Analysis of the constituents ofPiper methysticum by gas chromatography methane chemical ionization mass spectrometry. New constituents of kava resin

Methane chemical ionization mass spectrometry has been used to investigate the components of kava resin prepared by solvent extraction of commercial Piper methysticum Forst. All the known constitutents of this resin were identified together with several new compounds which of formally result from decarboxylation of the 4-methoxy-2-pyrone ring system in the known compounds. Chemical ionization mass spectrometry is a useful probe for the identification of these compounds because all gave easily recognized protonated molecular ions and the fragmentation patterns were related to molecular structure. Using this technique, the steam distillation products of commercial P. methysticum were identified, as was the product distribution from base hydrolysis of the known kava pyrone, yangonin.

Positive and negative ion methane chemical ionization mass spectrometry of amino acid pentafluorobenzyl derivatives

Condensation of pentafluorobenzyl bromide with α-amino acids under basic conditions using a brief reaction time generates amino acid-PFB derivatives. These compounds have satisfactory gas chromatographic properties and their methane positive and negative ion mass spectra have been recorded. These spectra contain few fragment ions and the negative ion mass spectra are dominated by a single anionic species making them suitable for selected ion monitoring experiments for the quantification of amino acids. Using Leu and Tyr as two typical examples we have found that negative ion chemical ionization mass spectrometry generates an increase of 250 to 300 times that observed for the same compounds under positive ion conditions.

Detection of gaseous organophosphorus compounds using secondary ion mass spectrometry

Molecular secondary ion mass spectrometry (SIMS) has been investigated for sensitivity and selectivity in the analysis of gaseous organophosphorus compounds. Abundant analyte ions were observed when the gaseous organophosphorus compounds were admitted into the secondary ion source, where a matrix was under primary ion bombardment. The best matrix for the detection of dimethyl methylphosphonate (DMMP), trimethyl phosphate (TMP), and diisopropyl methylphosphonate (DIMP) was determined to be polyphosphoric acid. The abundance of secondary analyte ions was observed to be linear with the introduction rate of gaseous analyte. The introduction rate necessary to produce a 3:1 signal-to-noise ratio in the intensity of secondary protonated molecular ions from DMMP was estimated to be 4 x 10/sup -11/ mols/sup -1/. Substantially more analyte fragmentation is observed by using SIMS than by using methane chemical ionization mass spectrometry. Ten compounds representative of other compound classes were investigated in the same manner as the organic phosphonates; characteristic secondary protonated molecular ions were detected from amines only.

Positive and electron capture negative ion methane chemical ionization mass spectrometry of pyrrolizidine alkaloids.

Pulsed positive and negative ion methane chemical ionization mass spectrometry of pyrrolizidine alkaloids is reported. Positive ion spectra are characterized by a high relative abundance of [MH]+ ions while the negative ion spectra exhibit ion peaks due to dissociative electron capture. Fragmentation in both positive and negative ion spectra primarily occurs at the ester groups with the positive charge residing with the pyrrolizidine ring system while the negative charge in contrast tends to reside with the necic acid moiety. Esterification at C-9 v. C-7 can be distinguished for non-cyclic esters of retronecine in the positive ion spectra.

Chemical ionization mass spectra of derivatized 1-benzyltetrahydroisoquinoline alkaloids

A study of the chemical ionization mass spectral characteristics of a series of derivatized 1-benzyltetrahy-droisoquinoline alkaloids is presented. Tetrahydropapaveroline and some related benzyltetrahydroisoquinolines were converted to their corresponding O-trimethylsilyl of N-trifluoroacetyl-O-trimethylsilyl derivatives prior to analysis by combined gas chromatographic methane chemical ionization mass spectrometry. The chemical ionization mass spectra of the derivatized alkaloids are compared to the electron impact mass spectra of the N-trifluoroacetyl-O-trimethylsilyl derivative of tetrahydropapaveroline, a representative benzyltetrahydroisoquinoline alkaloid. The effects of the nitrogen substituent and ion source pressure on the relative abundance of significant ions in the chemical ionization mass spectra of these alkaloids are also described.

Dimer formation in methane chemical ionization mass spectrometry of organic functionalities, including 2‐azaadamantane derivatives

AbstractThe methane chemical ionization mass spectra of 1‐hydroxy‐2‐azaadamantane, its lactolactam, and 1‐chloro‐2‐azaadamantanes exhibit high intensity dimeric species. These correspond to [2M+H]+ or stable fragments formed via gas phase chemical reactions, such as dehydration (aminol case) or dehydrohalogenation (chloroazaadamantanes). The tert‐amino chloroazaadamantane forms a stable [2M+C2H5]+ ion with much higher intensity than the [2M+H]+ ion. Similar dimeric species were observed with simple functionalities, including amide, amine, alcohol and alkene. Pressure, temperature and, apparently, steric effects play important roles. Structures are proposed for the various dimeric ions.

Absence of α-methyldopamine in rat striatum after chronic administration of d-amphetamine

Direct measurement by gas chromatography methane chemical ionization mass spectrometry of α-methyldopamine and α-methylnorepinephrine in rat striatum has shown the failure of these compounds to be accumulated in vivo after chronic administration of d-amphetamine despite the accumulation of α-methyltyramine, an immediate in vitro precursor. Further, both α-methyldopamine and α-methyltyrosine. These data suggest striatum after administration of α-methyltyrosine. These data suggest that, after administration of α-methyltyrosine, α-methyldopamine is formed via decarboxylation of α-methyldopa and not from hydroxylation of α-methyltyramine. Finally, our results indicate that α-methyldopamine does not play a role in the development of tolerance to d-amphetamine.

The identification of bile acid methyl esters by gas chromatography methane chemical ionization mass spectrometry.

Methane chemical ionization mass spectrometric data and gas chromatography retention parameters are reported for 31 bile acid methyl esters. The group includes both saturated and unsaturated compounds with up to three keto or hydroxyl groups. Major ions include the quasimolecular ions and fragments resulting from the loss of neutral species such as methanol, water and methane. The combination of gas-liquid chromatography retention and mass spectral data is sufficient for an unequivocal distinction among all the bile acids studied. Application of this data to the identification of bile acid metabolites is cited.