摘要:

AbstractKnudsen cell mass spectrometric measurements are reported on the composition of vapour over solid and fused NaI, CsI, HoI3, DyI3, (NaI + HoI3), (NaI + DyI3, (CsI + HoI3) and (CsI + DyI3systems. For the determination of evaporation thermodynamics, the assignment of the essential ions to their neutral precursors was carried out by determining ionization efficiency curves. Due to the spread in electron energy, the linear extrapolation and vanishing current methods, which are generally used in high temperature mass spectrometry for evaluation of efficiency curves, could be used with limitations only. The analytical energy‐distribution difference method was used to determine the fine structure of the ionization efficiency curves. The method uncovered relationships between the detected ions and neutral vapour‐phase species, and served to determine thermodynamic data with improved precis

ISSN:0951-4198    

DOI:10.1002/rcm.1290030702

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractCollisionally activated decomposition spectra derived from normal nucleosides and nucleotides have been studied using a four‐sector tandem mass spectrometer. The selectivity for a precursor ion has been improved by the use of the first two sectors as a double‐focusing mass spectrometer, and the mass resolution of daughter spectra has been enhanced using the next two sectors as a second double‐focusing mass spectrometer. Reliable and reproducible data with respect to the structure of nucleosides and nucleotides have been obt

ISSN:0951-4198    

DOI:10.1002/rcm.1290030703

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractSequential daughter‐ion‐scanning analyses of small peptides have been performed using a hybrid tandem instrument of BEqQ configuration. Precursor ions are selected by B and allowed or induced (by high‐energy collisional activation) to decompose in the region preceding E. Decoupling of E from the accelerating voltage permits the selection of the first‐generation daughter ion whilst retaining appropriate float voltages for the quadrupole assemblies. The daughter ion selected by E is further subjected to low‐energy collisional‐activation dissociation (CAD) in q and the fragment‐ion spectrum is obtained by scanning Q. The sequential daughter‐ion‐scanning technique has been used to establish that ‘internal’ fragments of the types, (AY′) and (BY′), are formed via initial Y‐type cleavage. Fragmentation of a protonated peptide (angiotensin III) by loss of the C‐terminal amino acid residue, yielding a (B n′+ OH) ion, is reported for the first time. This process is analogous to that previously descri

ISSN:0951-4198    

DOI:10.1002/rcm.1290030704

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractThe fragmentation of some carbamoyl‐ and thiocarbamoylcyclohexanones under electron ionization has been investigated by means of high‐ and low‐resolution mass spectrometry and deuterium labelling. Some characteristic fragmentation processes observed in the mass spectra of thiocarbamoylcyclohexanones indicate that both keto and enol forms of their molecular ions exist in the gas phase. The fragmentation data for carbamoylcyclohexanone show that the keto form is largely predominant in the keto‐enol tautomeric equi

ISSN:0951-4198    

DOI:10.1002/rcm.1290030705

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractSecondary‐ion mass spectrometry, using Cs+ion bombardment of solid and liquid matrices, has been implemented on a quadrupole ion trap. Tetraalkylammonium cations and protonated peptides, generated in an external source using a pulsed primary‐ion beam, are injected into the ion trap where they are decelerated and trapped in the course of collisions with the helium bath gas. The contents of the trap are then examined by recording a mass spectrum using the mass‐selective instability scan. To improve performance in the examination of these trapped ions, the technique of axial modulation is used to cause resonance ejection of ions from the trap during the mass‐analysis step. The supplementary AC voltage applied to the end‐caps causes resonant ejection of ions atqzvalues below those which correspond to the normal stability limit. This is demonstrated to increase the mass limit of a commercial ion trap from 650 Da to approximately 1300 Da with no loss in resolution or sensitivity, and to more than 20 000 Da at reduced se

ISSN:0951-4198    

DOI:10.1002/rcm.1290030706

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractChemotaxonomic studies are frequently limited by the volume of data obtained and the difficulty of reducing this to statistically interpretable results. This paper describes the use of a straightforward procedure for relating the pattern of occurrence of sterols in fungi, analysed by mass spectrometry, to their classification.

ISSN:0951-4198    

DOI:10.1002/rcm.1290030707

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractThe production of high‐mass quasimolecular ions from proteins by matrix‐assisted ultraviolet laser desorption is described. A simple time‐of‐fight system using a Q‐switched frequency‐quadrupled Nd‐YAG laser to desorb protein molecules is shown to have a mass range of up to 116 000 u by the observation of intact, singly charged quasimolecular ions from 700 fmol of β‐galactosidase subunit (mol.wt = 116 336 Da). Both positive‐ and negative‐ion spectra of proteins are shown. Four new matrix materials, with properties as good as or better than nicotinic acid, are described. A mass resolution of approximately 500 (full width at half maximum definition) is demonstrated for proteins with mol.wt<20 000 Da. Product species, formed by fast photochemical reactions in the matrix, are observed to form adduct ions with protein molecules. These adduct ions are a significant cause of the observed broadness of protein quasimolecular ion peaks. The practical physical considerations in detection of large‐mass quasimolecular ions from laser desorption, such as detector over

ISSN:0951-4198    

DOI:10.1002/rcm.1290030708

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractPyrolysis‐desorption/chemical‐ionisation mass spectrometry (PyD/CIMS), using ammonia as ionization gas, was employed to investigate the influence of potassium hydroxide on the pyrolytic behaviour of glucans. The mass spectrum of native amylose, a 1 → 4 linked α‐D‐glucan, revealed an ion series pointing to desorption of intact 1,6‐anhydro‐oligosaccharides. Ions indicating oligomers up to the nonamer were observed. Addition of trace amounts of potassium hydroxide to amylose resulted in reduction in the size of the 1,6‐anhydro‐oligosaccharide ions and a simultaneous increase of ions resulting from ring rearrangements. Larger amounts of potassium hydroxide led to a complete loss of mass spectral information at the oligomer level.Similar mass spectrometric distributions in the PyD/CIMS data of a potassium hydroxide extracted tobacco fraction clearly reveal that alkali remnants must be present in this sample, which severly reduce the mass spectrometric information from polysaccharide oligomers. It is important to evaluate the role of inorganics on the thermal activation and subsequent fragmentation of biopolymers in Py

ISSN:0951-4198    

DOI:10.1002/rcm.1290030709

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractThe ion trap detector (ITD) is effective in the analysis of terpenoic mixtures from essential oils. ITD spectra are compared in library searches with spectra from a quadrupole mass spectrometer. ITD generally leads to lower FIT values, although its efficiency in terms of structural identification is comparable to that of quadrupolar systems.

ISSN:0951-4198    

DOI:10.1002/rcm.1290030710

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

ISSN:0951-4198    

DOI:10.1002/rcm.1290030711

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY