Isobutane Chemical Ionization Research Articles

ChemInform Abstract: TEMPERATURE DEPENDENCE OF THE ISOBUTANE CHEMICAL IONIZATION MASS SPECTRA OF OPEN‐CHAIN AND CYCLIC ALCOHOLS; STRUCTURAL, STEREOCHEMICAL AND MOLECULAR SIZE EFFECTS. A REEVALUATION OF THE ISOBUTANE CHEMICAL IONIZATION OF ALCOHOLS

Chemischer InformationsdienstVolume 14, Issue 31 Physical Organic Chemistry ChemInform Abstract: TEMPERATURE DEPENDENCE OF THE ISOBUTANE CHEMICAL IONIZATION MASS SPECTRA OF OPEN-CHAIN AND CYCLIC ALCOHOLS; STRUCTURAL, STEREOCHEMICAL AND MOLECULAR SIZE EFFECTS. A REEVALUATION OF THE ISOBUTANE CHEMICAL IONIZATION OF ALCOHOLS F. J. WINKLER, Search for more papers by this authorF. O. + GUELACAR, Search for more papers by this authorF. MERMOUD, Search for more papers by this authorA. BUCHS, Search for more papers by this author F. J. WINKLER, Search for more papers by this authorF. O. + GUELACAR, Search for more papers by this authorF. MERMOUD, Search for more papers by this authorA. BUCHS, Search for more papers by this author First published: August 2, 1983 https://doi.org/10.1002/chin.198331070Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume14, Issue31August 2, 1983 RelatedInformation

Temperature Dependence of the Isobutane Chemical Ionization Mass Spectra of Open‐chain and Cyclic Alcohols; Structural, Stereochemical and Molecular‐Size Effects. A reevaluation of the isobutane chemical ionization of alcohols

AbstractThe temperature dependence of the isobutane chemical ionization (CI.) mass spectra of 54 open‐chain, cyclic and unsaturated C5‐ to C10‐alcohols was studied at temperatures ranging from 60 to 250°, and enthalpy changes were calculated for the corresponding main reactions of typical alcohols.The CI. reactivity is controlled by the temperature and the substrate structure as usual, and in addition, by the molecular size. The combination of thermal, structural and substrate‐size effects leads to the following main conclusions.At low‐reactivity conditions, i.e. at 150° or less, the alcohols with less than 11 C‐atoms give four distinct types of spectra, with (M – OH)+ usually as the base peak. The characteristic ions are MC4H9+ and (M – H)+ for primary, MH+ and (MC4H9 – H2O)+ for secondary, (MC4H9 – H2O)+ for tertiary and allyl‐type alcohols. Configurational assignments of stereoisomeric alcohols are also possible, by means of steric compression and shielding effects. The MH+/(M – OH)+ ratio in the spectra of epimeric methylcyclohexanols is at least 3 to 4 times higher for the isomers with mainly axial OH‐group conformation compared to the equatorial isomers. Stereospecific (M ‐ H)+ ions are apparently formed from trans‐2‐methylcyclopentanol and endo‐norbornan‐2‐ol by a favorable abstraction of the unshielded H(α)‐atoms versus normal behavior of the other epimers.While the spectra recorded at 200° show almost exclusively (M – OH)+ ions, those at 250° give nevertheless some C‐skeleton information through the temperature dependent decomposition of the (M – OH)+ ions.

含窒素複素芳香族化合物の化学イオン化マススペクトル

Chemical ionization (CI) mass spectra with methane or isobutane reagent gas were measured in order to elucidate their characteristics for 41 nitrogen containing heteroaromatic compounds such as pyridine, quinoline, indole, pyrrole, pyrazine, pyrimidine, pyridazine, imidazole and their alkylsubstituents. The methane and isobutane CI mass spectra of these compounds gave the same ionic species as in alkylbenzenes except (M-28)+ in 2-propylpyridine and 2-(3-pentyl) pyridine. It was estimated that (M-28)+ was formed by McLafferty rearragement accompanying elimination of ethylene from the molecular ion. The ion abundance of each ion was fairly different compared with the case of alkylbenzenes, and it was remakable in terms of providing large ion abundance of MH+ based on high basicity of compounds. The fact that MH+ were the base peaks in all cases was very useful for the estimation of molecular weights.

Qualitative analysis of trimethylsilylated daunosamine and N-alkylated analogs by gas chromatography-mass spectrometry

A gas chromatography-mass spectrometric method is described for the precise chemical identification of the sugar residues of daunorubicin and the N-alkylated anthracycline analogs. Parent drug or purified biliary metabolites from rabbits were hydrolyzed with 0.2 n HCl for 15 to 30 min at 100°C. The generated aglycones were removed by chloroform extraction, and the remaining aqueous extract was evaporated under nitrogen. The residue was dissolved in trimethylsilylimidazole/pyridine. The resulting silylated daunosamine moiety was chromatographed on a 3% OV-17 column coupled via a jet separator to the source of a mass spectrometer. The natural α-anomer, which was assigned to the major peak, eluted first. Electron ionization analysis of the silylated sugars displayed extensive fragmentation. Isobutane chemical ionization provided spectra with intense protonated molecular ions [MH] + and limited fragmentation. In all cases the later eluting β-anomer gave identical although more intense fragments than the α-anomer. Common fragment ions seen were [MH] +, [MH-90] +, [MH-116] +, and [MH-130] +. Daunosamine has been detected from as little as 5.7 nmol daunorubicin. N-Benzyldaunorubicinol was identified as the major biliary metabolite in rabbits following dosing with 3.0 mg/kg N,N-dibenzyldaunorubicin. This method has been applied to the analysis of glucosamine and may find utility in the analysis of many other amino sugars.

Electron impact and methane, isobutane and ammonia chemical ionization mass spectra of peptide amides related to melanostatin (Pro-Leu-Gly-NH2)

Eighteen peptide amides related to Melanostatin, Pro-Leu-Gly-NH2, were studied by electron impact and methane, isobutane and ammonia chemical ionization mass spectrometry. In general the methane and isobutane chemical ionization spectra, which were qualitatively similar, gave more pertinent structural information than the electron impact spectra. In ammonia chemical ionization, both the peptide amides and their fragment ions reacted with unionized reagent gas to give protonated peptide amides together with some other fragments not observed in methane or isobutane chemical ionization. Moreover, a Melanostatin analogue containing a dehydroproline residue underwent aromatization and double bond reduction in chemical ionization, and the two reactions may possibly have been linked.

Bioids : X. Identification of formose sugars, presumable prebiotic metabolites, using capillary gas chromatography/gas chromatography—mas spectrometry of n-butoxime trifluoroacetates on OV-225

Most monosaccharides, including 3-uloses and branched-chain species formed by the autocatalytic condenstation of formaldehyde, have been separated by capillary gas chromatography (GC) and isobutane chemical ionization GC—mas spectrometry (MS) on OV-225 of the trifluoroacetyl n-butoximes, and identified using commercial sugars, oxidation products of alditols and aldolization products of formaldehyde and/or glycolaldehyde and trioses, and by selected ion monitoring. The product pattern of a reaction of 0.156 M formaldehyde with 0.036 M calcuim acetate and 0.087 M sodium hydroxide at 40°C, started by the addition of 0.55 m M glycolaldehyde is reported. In addition to the already known trioses, tetroses, pentoses and hex-2- uloses, also pent-2-uloses (20-% including 13% of 2-xylulose), 6.5% of hex-3-uloses, 5% of d, l-3-C-hydroxymethyltetrose (apiose) and 6.3% of branched hexoses were found; 90.3% of the total volatile derivatives of 3–6-carbon sugars have been identified; conspicuously, 50–80% of the reacted formaldehyde does not afford volatile sugar derivatives. Because of its autocatalytic kinetics, in a prebiotic scenario a formol reaction could evolve into a self-organizing non-enzymatic system steadily producing sugars, including branched-chain sugars, as precursors of amino acids, of the isoprene moiety and of the branched chains of valine and leucines.

Formation of 6-dimethylcarbamyloxy-dGuo, 6-dimethylamino-dGuo and 4-dimethylamino-dThd following in vitro reaction of dimethylcarbamyl chloride with calf thymus DNA and 6-diethylcarbamyloxy-dGuo following in vitro reaction of diethylcarbamyl chloride with calf thymus DNA

The rodent carcinogens dimethylcarbamyl chloride (DMCC) and diethylcarbamyl chloride (DECC) react with dGuo (pH 7.0–7.5, 37°C, 4 h) to form the O 6-acyl derivatives 6-dimethylcarbamyloxy-2′-deoxyguanosine (6-DMC-dGuo) and 6-diethylcarbamyloxy-2′-deoxyguanosine (6-DEC-dGuo), respectively. Reaction of DMCC with dThd under identical conditions yielded 4-dimethylamino-thymidine (4-DMA-dThd). Compounds 6-DMC-dGuo and 6-DEC-dGuo undergo a nucleophilic aromatic substitution reaction with dimethylamine (DMA) to form 6-dimethylamino-2′-deoxyguanosine (6-DMA-dGuo) via displacement of the C-6 dialkylcarbamyloxy moiety. The substitution reaction did not take place when diethylamine or NH 3 were substituted for DMA. The structures of the new compounds 6-DMC-dGuo, 6-DEC-dGuo, 4-DMA-dThd and 6-DMA-dGuo were deduced from chemical analyses and syntheses, UV and nuclear magnetic resonance (NMR) spectra and electron impact, isobutane chemical ionization and source insertion isobutane chemical ionization mass spectra. It was postulated that 4-DMA-dThd was formed following reaction of the transient intermediate 4-DMC-dThd with DMA formed by hydrolysis of DMCC. Calf thymus DNA was reacted in vitro with DMCC (pH 7.0–7.5, 37°C, 4 h) and the modified DNA hydrolyzed enzymatically to 2′-deoxynucleosides. Compounds 6-DMC-dGuo, 4-DMA-dThd and 6-DMA-dGuo were identified in the hydrolysate by high-pressure liquid chromatography (HPLC). In an indentical manner 6-DEC-dGuo was identified following in vitro reaction of DECC with calf thymus DNA. Compounds 6-DEC-dGuo and 6-DMC-dGuo possess novel structures with respect to the types of adducts known to be formed between carcinogens and bases in DNA. The implications of these findings with respect to chemical mutagenesis and carcinogenesis is discussed. The structural relationship between N 4-dimethyl-5-methylcytosine (4-dimethylamino-Thy) formed in DNA following in vitro reaction with DMCC and 5-methylcytosine, the only modified base found in vertebrate DNA is noted.

Mass spectra of 1,6:2,3- and 1,6:3,4-dianhydro-β-D-hexopyranose derivatives: Formation of cluster ions assisted by participation of neighbouring acyloxy groups

Chemical ionization and electron impact mass spectra of 1,6:2,3-and 1,6:3,4-dianhydro-β-D-hexopyranose derivatives are reported. The methane and isobutane chemical ionization mass spectra of both positional and configurational isomers differ significantly, while the electron impact mass spectra of stereoisomers are hard to discern. Examination of the isobutane chemical ionization mass spectra indicates that only those isomers containing the acyloxy group and the oxirane ring in the trans position give stable [M+C4H9]+ ions, otherwise these ions are of negligible abundance. This observation is interpreted in terms of participation of the acyloxy group in oxirane ring opening. This feature of the chemical ionization mass spectra can be used for stereochemical assignment.

Analysis of N-acetyl-N,O,S-permethylated peptides by combined liquid chromatography-mass spectrometry

Initial results are presented on the liquid chromatography-mass spectrometry (LC-MS) of N-acetyl-N,O,S-permethylated oligopeptides using a moving belt interface for the sequence analysis of the peptides. Using a quadrupole MS, it has been found that isobutane chemical ionization provides good intensity [M + 1]+ ions, as well as well-defined N- and C-terminal fragment ions. It is shown that C-methylated peptides can be separated by LC and identified by MS. Examples are given on the LC-MS of N-acetyl-permethylated Leu-enkephalin as well as a mixture of derivatized peptides. In all cases sequence information is available by the LC-MS approach. Finally, initial and promising attempts at predicting chromatographic retention in a linear gradient condition in reversed-phase LC for the derivatized peptides are presented. These results establish that sequence analysis of permethylated peptides by LC-MS can be achieved.

Sequence analysis of polypeptides by collision activated dissociation on a triple quadrupole mass spectrometer.

A new approach to the direct sequencing of oligopeptides in complex mixtures is described. Mixtures of [2Ho]/[2H3]-N-acetylated and N,O-permethylated peptides are analyzed by collision activate dissociation on a triple quadrupole mass spectrometer using isobutane chemical ionization. Analysis of the collision activated dissociation spectra enables peptide sequences to be deduced. Use of electron capture negative chemical ionization for the sequence analysis of neuropeptides at the picomole level is also described.

The isolation and characterization of 3-(2-carboxyethyl)cytosine following in vitro reaction of β-propiolactone with calf thymus DNA

The new adduct 3-(2-carboxyethyl)cytosine (3-CEC) was isolated following in vitro reaction of the carcinogen β-propiolactone (BPL) with calf thymus DNA. The structure of 3-CEC was confirmed by synthesis from BPL and dCyd. Reaction of BPL with cCyd (pH 7.0–7.5, 37°C) gave 3-(2-carboxyethyl)deoxycytidine (3-CEdCyd) (9% yield) and 3, N 4-bis(2-carboxyethyl)deoxycytidine (3, N 4-BCEdCyd) (0.6% yield). 3-CEdCyd and 3, N 4-BCEdCyd were hydrolyzed (1.5 N HC1, 100°C, 2 h) to 3-CEC and 3, N 4-bis(2-carboxyethyl)cytosine (3, N 4-BCEC), respectively. The structure of 3-CEC was assigned on the basis of UV and NMR spectra and the electron impact (EI) mass spectra of 3-CEC and a tri-trimethylsilyl (TMS) derivative of 3 CEC as well as deuterated (d 27) tri-TMS derivative of 3-CEC. The structure of 3, N 4-BCEC was assigned on the basis of UV spectra and the EI mass spectra of a tri-TMS derivative. EI and isobutane chemical ionization mass spectra of 3-methylcytosine (3-MeCyt) and a di-TMS derivative of 3-MeCyt were obtained and were helpful in deducing the structures of 3-CEC and 3, N 4-BCEC. This is the first report of the alkylation by BPL of an exocyclic atom on a base in DNA. Compound 3, N 4-BCEC was not detected in BPL-reacted calf thymus DNA. The relative amounts of 1-(2-carboxyethyl)adenine (1-CEA), 7-(2-carboxyethyl)guanine (7-CEG), 3-(2-carboxyethyl)thymine (3-CET) and 3-CEC isolated from BPL-reacted DNA following perchloric acid hydrolysis were 0.23, 1.00, 0.39 and 0.41 respectively, when the alkylation reaction was conducted in phosphate buffer at 0–5°C and pH 7.5 and 0.10, 1.00, 0.29 and 0.28 respectively when the reaction was conducted in H 2O at 37°C and pH 7.0–7.5.

Loss of H2O from M + t‐Butyl Complex Ions of Benzyl Alcohol in Isobutane Chemical Ionization Mass Spectrometry

AbstractIn isobutane chemical ionization mass spectrometry benzyl alcohol exhibits ions at m/z 147 (‘M + 39’) that arise by a loss of H2O from [M + C4H9]+, i.e. ‘M + 57’ complex ions. Electrophilic aromatic substitution of a proton at an ortho‐position of neutral C6H5CH2OH with [t‐C4H9]+ and, alternatively, nucleophilic substitution of H2O at the benzylic carbon in \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C_6 H_5 CH_2}\mathop {\rm O}\limits^+ {\rm H}_2 $\end{document} with CH2C (CH3)2 are discussed as possible pathways. Evidence in favor of the latter is derived from the analysis of C6D5CH2OH and C6H5CD2OH for the origin of the H‐atoms lost in H2O. The inferred ion structure of m/z 147 is verified by mass‐analyzed ion kinetic energy (MIKE.) measurements of its collision‐activated (CA.) decomposition. MIKE./CA. spectra of mass‐selected m/z 147 ions, once generated by (CI(i‐C4H10) from benzyl alcohol and, once, from 2‐methyl‐4‐phenyl‐2‐butanol match closely and, thus, reflect identical ion structures. With reference to the simple genesis of this ion from the latter precursor, the structure in question can be concluded to be \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C_6 H_5 CH_2 CH_2}\mathop {\rm C}\limits^+ ({\rm CH}_3)_2 $\end{document} .

Fragmentation of the protonated stereoisomers of 5,7‐Undecanediol and its bis(trimethylsilyl) ether under conditions of isobutane chemical ionization

AbstractThe chemical ionization induced fragmentation behaviour of an open chain model compound, 5,7‐undecanediol (meso and d,l stereoisomers), is studied and compared with that of previously studied alicyclic models, e.g. cyclohexanediols (cis and trans isomers). In close analogy to the latter, the major fragmentation processes are the one‐ and twofold loss of H2O from the protonated molecules [MH]+. As borne out by appropriately deuterium labelled analogues, the first loss of H2O is invariably a ‘clean’ heterolysis. The second loss is considerably more complex in that 1,3‐ and 1,4‐elimination processes occur concurrently. While the 1,4‐mode may be a direct elimination process in both types of compounds, the 1,3‐mode is rearrangement induced in both. Whereas skeletal rearrangement (ring contraction) precedes this 1,3‐elimination in the alicyclic models, hydrogen rearrangement (1,2‐hydride shift) precedes it in the open chain model. No pronounced stereochemical effect is observed on the mechanistic course of the elimination processes, but is observed in their relative ease. The trimethylsilyl ethers of the stereoisomers of 5,7‐undecanediol are also studied for analogous reactions, and are discussed in this context.

Quantitation of fourteen urinary α-amino acids using isobutane gas chromatography chemical ionization mass spectrometry with13C amino acids as internal standards

Isobutane chemical ionization gas chromatography mass spectometry of the N-trifluoroacetyl-carboxy-n-butyl ester derivatives of amino acids, using a commercial per-13C-amino acid mixture as internal standards, provided a sensitive and specific method for quantitative analysis of fourteen urinary alpha-amino acids. A computer controlled quadrupole mass spectrometer was used in a selected ion monitoring mode to record the ion current due to the protonated molecular ions of each alpha-amino acid/13C analogue pair. BASIC programmes located peak maxima, and using previously established standard curves, calculated the amino acid content on the bases of both peak height and peak area ratios. Duplicate amino acid analyses are possible on 5 microliter of urine. Instrumental analysis required 25 minutes, automated data processing 10 minutes, and sample preparation 2 hours. Detection limits approached 1 ng with a typical mean standard deviation of 2% for the instrumental analysis.

Chemical ionization and electron impact mass spectra of alicyclic substituted 2‐aryl‐1,3‐dithianes

AbstractThe methane and isobutane chemical ionization mass spectra of alicyclic substituted 2‐aryl‐1,3‐dithianes were examined by gas chromatography mass spectrometry. The protonated molecular ion was found to be of low abundance in the methane spectra, while a protonated cyclic sulfide cation (m/z 107) appeared as the base peak. A protonated molecular ion was the base peak when isobutane was used as the reagent gas. Electron impact mass spectra displayed weak molecular ions and were characterized by the m/z 106 fragment.

Identification of steroids by chemical ionization mass spectrometry.

Chemical ionization (CI) mass spectra of various natural and synthetic steroids have been studied using methane, isobutane, ammonia, trideuterioammonia and hydroxy anion as reagent gases. The CI spectra of steroids give simple and well characterized ions, which provide information about molicular weight as well as functionalities in the molecules. Trideuterioammonia exchanges rapidly with active hydrogens (e.g., OH, SH, COOH, NH2) in steroid molecules in the CI reaction and thus provides a convenient means of active hydrogen determination by mass spectrometry, Application of various CI processes to the analysis of steroids and conjugates have been made. Low levels of hydroxycholesterols in biological samples and in cholesterol autoxidation products were identified by the 4 ion patterns, [M+NH4]+, [M-OH+NH3]+, [M-0H]+ and [M-H2 O-OH]+, in ammonia CI. The position of hydroxy functions in the cholesterol side chain can be identified from the methane CI of hydroxycholesterol trimethylsilyl (TMS) derivatives. Sterol carboxylic esters can be identified as the ammonium adduct ion of the intact molecule, [M+NH4]+, in ammonia CI. Isobutane and hydroxy anion CI spectra of the steroid esters give abundant ion fragments of both steroids and carboxylic acid moieties. Identification of free bile acids and steroid glycosides without derivatization is also feasible with the CI process when ammonia is used as reagent gas.

Electron impact and chemical ionization mass spectra of catechol derivatives from insect cuticle

Electron impact and isobutane chemical ionization mass spectra of a series of catechol derivatives isolated from hydrolysates of insect cuticle were studied. Electron impact mass spectrometry resulted in sufficient information for the identification of all the compounds. Furthermore, characteristic fragmentation patterns were demonstrated, which allow classification of the catechol derivatives according to the substituent next to the aromatioring of the aliphatic sidechain. By chemical ionization mass spectrometry [M + H]+ions were the base peak in most spectra, but for some compounds [M + H]+ was absent, and [M + H - H2O]+ the base peak. In many of the CI spectra [2M + H]+ ions were present and in one case [3M + H]+. Chemical ionization mass spectrometry was unsuitable for the identification of the catechol derivatives investigated.

High precision isotopic ratio analysis of volatile metal chelates

High precision isotope ratio measurements have been made for a series of volatile alkaline earth and transition metal chelates using conventional GC/MS instrumentation. Electron ionization was used for alkaline earth chelates, whereas isobutane chemical ionization was used for transition metal studies. Natural isotopic abundances were determined for a series of Mg, Ca, Cr, Fe, Ni, Cu, Cd, and Zn chelates. Absolute accuracy ranged between 0.01 and 1.19 at. %. Absolute precision ranged between +-0.01-0.27 at. % (RSD +- 0.07-10.26%) for elements that contained as many as eight natural isotopes. Calibration curves were prepared using natural abundance metals and their enriched /sup 50/Cr, /sup 60/Ni, and /sup 65/Cu isotopes covering the range 0.1-1010.7 at. % excess. A separate multiple isotope calibration curve was similarly prepared using enriched /sup 60/Ni (0.02-2.15 at. % excess) and /sup 62/Ni (0.23-18.5 at. % excess). The samples were analyzed by GC/CI/MS. Human plasma, containing enriched /sup 26/Mg and /sup 44/Ca, was analyzed by EI/MS. 1 figure, 5 tables.

Isobutane chemical ionization mass spectrometry of β‐amino alcohols. Evaluation of populations of conformers at equilibrium in the gas phase

AbstractThe conformer populations of conformationally mobile β‐amino alcohols in the gas phase, can be evaluated from the relative intensity of the dehydration peak [MHH2O]+ in isobutane chemical ionization mass spectrometry.

Isolation of 3-(2-carboxyethyl)thymine following in vitro reaction of β-propiolactone with calf thymus DNA

3-(2-Carboxyethyl)thymine (3-CET) was synthesized from β-propiolactone (BPL) and dThd5′P at pH 9.0–9.5 via the intermediate 3-(2-carboxyethyl)thymidine-5′-monophosphoric acid (3-CEdThd5′P). 3-CEdThd5′P was converted to 3-CET by hydrolysis in 1.5 N HCl at 100°C for 2 h. The structure of 3-CET was assigned on the basis of UV spectra, electron impact (EI) and isobutane chemical ionization mass spectra and the EI mass spectrum of a trimethylsilyl derivative of 3-CET. BPL was reacted in vitro with calf thymus DNA at pH 7.5. 100 A units of BPL-reacted DNA yielded, following perchloric acid hydrolysis and preparative paper chromatography, 3 A units of 3-CET. Reaction of BPL with the phosphodiester thymidylyl-(3′-5′)thymidine gave 3-(2-carboxyethyl)thymidylyl-(3′-5′)-3-(2-carboxyethyl)thymidine (∼3%). Phosphotriester formation was not detected.