摘要:

AbstractThe behaviour of four open‐chain analogues of crown ethers (polypodands) have been studied under both electron ionization and fast‐atom bombardment conditions with the aid of mass‐analyzed ion kinetic energy spectroscopy and accurate mass measurements. In electron ionization, extensive fragmentations, closely related to the original structures, are observed, while fast‐atom bombardment, leading to the formation of abundant protonated molecules, allows easy establishment of the molecular weight. The presence of odd‐electron cations in distonic form and the occurrence of cyclization reactions are

ISSN:0951-4198    

DOI:10.1002/rcm.1290080402

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe electron ionization mass spectrometric behaviour of dimethylindiumN,N,N′‐trialkylethylenediamides and, for comparison, of trimethylindium adducts with the relatedN,N,N′‐trialkylethylenediamines, is discussed. The extensive decomposition processes observed under fast‐atom bombardment conditions are rationalized in terms of the condensed‐phase reactivity of the compounds

ISSN:0951-4198    

DOI:10.1002/rcm.1290080403

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractWe propose a new confirmatory method for testosterone doping in sport. The present method in use, based on measuring the testosterone/epitestosterone (T/E) ratio in urine, may miss suspicious cases, or lead to reporting cases in which the high ratio is natural. Synthetic testosterone has a13C abundance different from that of endogenous human testosterone. The connection of a gas chromatograph to an isotope‐ratio mass spectrometer via a combustion interface allows the measurement of the corresponding characteristic value (δ‰) for testosterone, its precursors, and its metabolites. To detect exogenous administration of testosterone, 30–40 mL of urine is suff

ISSN:0951-4198    

DOI:10.1002/rcm.1290080404

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe formation of deprotonated molecules, [M—H]−, of α‐tocopherol under fast‐atom bombardment (FAB) conditions has been discussed on the basis of a proton subtraction reaction between analyte and matrix molecules. The use of proton‐accepting matrices such as diethanolamine (DEA) and pentamethyleneglycol (PMG) gave higher intensities of the [M—H]−ion and more definitive spectral data than when other matrices, a 1:2 (v/v) mixture of thioglycerol (TG) and dithiothreitol (DTT), orm‐nitrobenzylalcohol (m‐NBA), were used. The order of proton acceptability evaluated for the matrices used was DEA>PMG>DTT>m‐NBA. It was concluded that the proton acceptability, which is measured by gas‐phase basicity or proton affinity, is a most important factor for the formation of both [M + H]+and [M—H]−ions under FAB conditions. Further, the formation of molecular ions, M+·, under FAB conditions and the formation of [M—H]−ions by electron impact have been

ISSN:0951-4198    

DOI:10.1002/rcm.1290080405

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe conformation of the rigid isomer pair ofcis‐ andtrans‐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 thecisandtransisomers were found to be different enough to permit the differentiation of the isomers. Each isomer exhibited distinctive fragmentation paths. The isobutane mass spectra of thecisisomer was dominated by the loss of H2O from the pseudo‐molecular ion, whereas the loss of C2H4O was the predominant fragment for thetransisomer. 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 frag

ISSN:0951-4198    

DOI:10.1002/rcm.1290080406

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractIn this paper we describe the underlying principles of, and demonstrate some of the attributes of, an inductive detector for use in time‐of‐flight mass spectrometry. Unlike a microchannel plate detector, the detection efficiency of the inductive detector is not dependent on ion velocity. Also, the inductive detector cannot be saturated in the same manner as a microchannel plate detector. Because the inductive detector detects only charged species, the neutral species normally observed in linear time‐of‐flight matrix‐assisted laser desorption/ionization spectra do not appear in spectra obtained with the inductive detector. Further, price and availability of the material needed to fabricate an inductive detector are virtually independent of detector size. Perhaps one of the most important features of the inductive detector is that it is a largely non‐destructi

ISSN:0951-4198    

DOI:10.1002/rcm.1290080407

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractA study of the electron impact mass spectrometry is reported for eight, stable, previously synthesized, enolic isomers of 2‐aroyl‐4‐aracyl‐1,3‐cyclopent

ISSN:0951-4198    

DOI:10.1002/rcm.1290080408

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractThe reaction of [1,3‐butadiene]+·with ethenc in the gas phase has been studied under low‐pressure conditions. Experiments were conducted in a Fourier transform ion cyclotron resonance spectrometer equipped with an external ion source. Two competitive reaction paths were identified: [CH2CHCHCH2]+·+CH2CH2→ [C5H7]++CH3·(Reaction I) and [CH2CHCHCH2]+·+CH2CH2→[C4H6]+·+C2H4(Reaction II). Deuterium labelling reveals that the methyl loss (Reaction I) is preceded by extensive H/D scrambling inside the transient collision complex and that the ethene molecule eliminated during Reaction II contains specifically one methylene group from the terminal positions of the 1,3‐butadiene radical cation and the other from the initial neutral ethene used as reactant. Measurements of deprotonation enthalpies indicate that the [C5H7]+ions produced via Channel I have the cyclopentadienyl structure. A reaction mechanism, corroborated by molecular orbital calculations (3‐21G), is proposed. It involves the initial formation of a distonic species [CH2CHCHCH2CH2CH2]+·as a key step and competitive processes such as [1 + 2] cycloadditon, 1,n‐hydrogen transfers and nonsy

ISSN:0951-4198    

DOI:10.1002/rcm.1290080409

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractBis‐aryliminopropadiene radical‐cations, [ArNCCCNAr′]+·, have been generated by dissociative ionization of isoxazolopyrimidine precursors and structurally characterized by collisional activation mass spectrometry; the corresponding neutral cumulenes have also been produced in neutralization‐reioniza

ISSN:0951-4198    

DOI:10.1002/rcm.1290080410

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY

摘要:

AbstractPerfusion high‐performance liquid chromatography (HPLC) combined with electrospray ion trap mass spectrometry (ITMS) was evaluated for the determination of neuropepetides in plasma. Perfusion HPLC offers the capability of resolving neuropeptides spiked into plasma in 5 min compared to the 30–60 min separations performed on packed capillary C18columns. Electrospray combined with the ITMS provides the ability to ionize these neuropeptides and mass analyze them with high sensitivity and specificity. Sub‐picomole quantities of neuropeptides injected on‐column could be specifically detected in a plasma matrix. The electrospray‐ITMS mass spectrum of each neuropeptide showed multiply charged ions which could be used to determine or confirm their molecula

ISSN:0951-4198    

DOI:10.1002/rcm.1290080411

出版商:Heyden&Son Limited    

年代:1994

数据来源: WILEY