摘要:

AbstractCollision‐induced dissociation (CID), also known as collision‐activated dissociation (CAD), is now central to the practice of mass spectrometry. The story of its discovery, fundamental basis, and its development as a technique applicable to different types of instruments has evolved over many decades. In this paper, these topics are explored by reference to and commentary on particular texts, chosen to represent milestones in the development of CID over the period 1910

ISSN:1076-5174    

DOI:10.1002/jms.1190300902

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractTandem mass spectra of a variety of adenine‐containing deoxynucleic acid anions obtained using collisional activation in a quadrupole ion trap are described. Data are reported for singly charged mono‐, di‐ and trinucleotide species, and also for multiply charged anions derived from tri‐, tetra‐, penta‐ and hexanucleotides. Attention is focused on the first step in the unimolecular decomposition of these species, namely the loss of the nucleobase. Specifically, the competition between the loss of the nucleobase as a neutral versus its loss as an anion is addressed within the context of a proposed proton‐bound intermediate consisting of the nucleobase and a phosphodiester linkage. The data are interpreted on the basis of the energy surface involved in the break‐up of the proton‐bound intermediate, which can explain why the competition between loss of a neutral versus charged base is strongly dependent upon the charge

ISSN:1076-5174    

DOI:10.1002/jms.1190300903

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractUnder fast atom bombardment, dihydroxybenzenes form predominantly the M+·and [M + Matrix]+·ions. The second field‐free region metastable decomposition of the [M + Matrix]+·ion involves the loss of a neutral molecule of the matrix. In the case of the hydroquinone–matrix adduct ion, elimination of both the matrix and hydroquinone are observed. Surprisingly, alkali metal cationization also leads to the formation of abundant radical cations in which the acidic hydrogens have been replaced with alkali metal. The degree of this exchange varies among the isomeric compounds. The facile formation of radical cations and their adducts appears to be due to various factors such as the ionization potentials, redox potentials and the proton affinities of the dihydroxybenzenes and the analyte‐matrix inte

ISSN:1076-5174    

DOI:10.1002/jms.1190300904

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractAnnth‐derivative Fourier transform complex spectrum, dnF(ω)/dωn, may be generated by multiplying at time‐domain signal by (−it)nbefore Fourier transformation. The resolving power of the magnitude‐modenth‐derivative spectrum, |dnF(ω)/dωn|, increases monotonically with increasing derivative order, but with concomitant decrease in signal‐to‐noise ratio. However, application of time‐domain exponential windowing can restore the signal‐to‐noise ratio. The combined derivatization–windowing process yields a magnitude‐modenth‐derivative Fourier transform spectrum with significantly enhanced resolution near the peak base without loss in signal‐to‐noise ratio. A theoretical analysis of the trade‐off between resolving power and signal‐to‐noise ratio for magnitude‐modenth‐derivative Fourier transform spectra as a function of time‐domain signal truncation, time‐domain windowing (exponential) and derivative order is presented. The method is demonstrated experimentally for Fourier

ISSN:1076-5174    

DOI:10.1002/jms.1190300905

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe determination of the mass discrimination effect of matrix‐assisted laser desorption ionization mass spectrometry (MALDI MS) over a widem/zrange was made by determining the relative amounts of prepurified protein monomer and dimer species present in reconstituted mixtures. Protein complexes were covalently cross‐linked with glutaraldehyde and monomeric and dimeric species were separated by gel filtration chromatography. Individual protein species were recombined in specific ratios and analyzed by both MALDI MS and sodium dodecyl sulfate polyacrylamide gel electrophoresis. The contributions of the peak areas of the doubly charged ions and singlycharged dimeric ions generated during the MALDI MS analyses relative to that of the singly‐charged [M + H]+species were measured. The calculation of mass discrimination for two different MALDI time‐of‐flight instruments showed the loss of a factor of ∼2.6 in relative peak area as them/zvalue doubled over them/zrange 30 000–145 000. An overall correction factor for mass discrimination is given which includes effects associated with sample preparation, sample desorption/ion formation, ion transmission and

ISSN:1076-5174    

DOI:10.1002/jms.1190300906

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe two‐dimensional mass spectra (metastable mapping) of ten biogenic amines derived from the amino acid 2‐phenylalanine are described. This technique permitted the identification of almost all the fragmentations of singly and doubly charged positive ions formed by electron impact and decomposing in the different parts of a reverse‐geometry mass spectrometer. The results obtained are discussed in order to establish the main fragmentation pathways common to all the amines belonging to the general class of 2‐phenylethylamines and to identify the fragmentations characteristic of eac

ISSN:1076-5174    

DOI:10.1002/jms.1190300907

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA simple procedure for the extraction and derivatization of α‐amino acids and α‐keto acids from human plasma is described. This stable isotope dilution method permits the quantification of isotopic enrichment and concentrations of several α‐keto and α‐amino acids simultaneously. The derivatization process results in methylformated, pentafluorobenzylated α‐amino acids and pentafluorobenzylated α‐keto acids. The derivatives proved to be very stable when stored at 5°C. Under electron capture chemical ionization (ECCI) conditions the derivatized amino acid produces abundant [M – PFB]−or [M – PFB – CH3OH]−anions; the α‐keto acid gives abundant [M – PFB]−anions. The method was applied to the analyses of 100 μl plasma samples in studies on protein metabolism. For the determination of concentrations [α‐ketoisocaproic acid (α‐KIC), Leu, Phe and Tyr] and enrichments ([1‐13C]‐α‐KIC, [1‐13C]‐Leu, D5‐Phe, D2‐Tyr, D4‐Tyr), resulting from administered tracers, the corresponding [M – PFB]−or [M – PFB – CH3OH]−anions were monitored. Higher labelled analogues were used as internal standards. The overall sensitivity was suf

ISSN:1076-5174    

DOI:10.1002/jms.1190300908

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe CH 3+adducts of benzaldehyde, acetophenone, propiophenone and butyrophenone were prepared using CH3FCH4and CH3ClCH4mixtures under chemical ionization conditions and the unimolecular and collision‐induced fragmentation reactions of their adduct ions were studied. For comparison, the fragmentation reactions of the protonatedp‐methylphenyl alkyl ketones were studied as models of the ring‐methylated species and the fragmentation reactions of [C6H5C(R)OCH3]+, produced by electron impact ionization of the appropriate methyl ether, were studied as models of theO‐methylated species. From these comparisons it is concluded that methyl cation addition occurs predominantly at the carbonyl oxygen under our experimental conditions. However, for methyl‐cationated acetophenone there is extensive migration of the methyl group from the oxygen to the ring prior to fragmentat

ISSN:1076-5174    

DOI:10.1002/jms.1190300909

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe metastable ion (MI) and collision‐induced dissociation (CID) mass spectra of five C3H6S+·isomers were examined. The MI mass spectra were virtually identical, which suggests that C3H6S+·ions having a substantial amount of internal energy can freely interconvert and isomerize into a common structure prior to fragmentation. However, the CID mass spectra are distinctly different and the differences can be related to the structure of the C3H6S+·isomers. It was even possible to distinguish the distonic ion H2CCH2SCH2+·from its conventional counterpart. The smaller amount of internal energy of the ions probed in CID experiments obviously limits isomeriz

ISSN:1076-5174    

DOI:10.1002/jms.1190300910

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractNegative‐ion electrospray mass spectrometry was used to determine directly both glycosidic linkage position and anomeric configuration in the complete glucopyranosyl disaccharide series without the need for derivatization or tandem mass analysis. A series of empirical criteria were developed which first differentiate between the linkage positions and then the anomeric configurations using selected diagnostic peaks and their relative intensities. The use of standard mass spectral library searching methods for structural analysis was also investigate

ISSN:1076-5174    

DOI:10.1002/jms.1190300911

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY