摘要:

AbstractThe presence of a few mol per cent of Ca2+ions considerably modified the252Cf plasma‐desorption mass spectrum of a phosphorylated glycolipid. In the negative‐ion mode, increasing amounts of Ca2+caused gradual disappearance of the spectrum; it was quenched at the molar ratio 3 Ca2+/4 glycolipid. Clusters as big as 5500 were observed at certain ratios of Ca2+/glycolipid. Similar, but less pronounced effects were seen in the positive‐ion

ISSN:0951-4198    

DOI:10.1002/rcm.1290030602

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractA simply designed silicon rubber membrane interface was used as a gas/liquid separator. This technique is based on the selectivity of the membrane. The combination of the membrane interface and a quadrupole mass spectrometer results in a simple and inexpensive instrument which can be used for both quantitative and qualitative determination of volatile compounds in aqueous solution. The response of the membrane‐interface/mass spectrometer to several volatile organic compounds in water was investigated. The detection limit of this instrument can be as low as the sub ppm range with a response time of a few minute

ISSN:0951-4198    

DOI:10.1002/rcm.1290030603

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractQuantitation of cyclic nucleotide phosphodiesterase activity by means of fast‐atom bombardment (FAB) mass spectrometry with mass‐analysed ion kinetic energy (MIKE) spectrum scanning is described. Characteristic peaks of the substrate, cyclic AMP, and product, AMP, were identified in positive‐ion FAB mass spectra and MIKE scans of the protonated molecules. By spiking enzyme incubates with known quantities of cyclic AMP and AMP and measuring peak heights in the MIKE spectra of both spiked and unspiked samples, the concentrations of cyclic AMP and AMP in solution at the end of a series of enzyme incubations have been estimated. From the data obtained theKmandVmaxof the enzymes were calculated as 181 μM and 28.6 nmol/min respectively, showing excellent agreement with values of the Michaelis constant,Km=205 μM and the maximum velocityVmax=33.2 nmol/min obtained by radioactiv

ISSN:0951-4198    

DOI:10.1002/rcm.1290030604

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractHigh‐performance liquid chromatography (HPLC) in combination with thermospray mass spectrometry (LC/TSP‐MS) is an important method for molecular weight determination of unknown compounds. In addition to the well‐known ammonium acetate buffer (NH4OAc) the use of methylammonium acetate (CH3NH3OAc) in the positive‐ and ammonium formate (NH4OFo) in the negative‐ion mode is recommended. Performing a second run with these buffers, even from spectra with only one single quasimolecular ion, an unequivocal molecular weight can be obtained. For correct assignment, the shift in mass of the corresponding quasimolecular ions in each mode is used. Finally, the use of a second buffer greatly facilitates the recognition of superimposed H

ISSN:0951-4198    

DOI:10.1002/rcm.1290030605

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractFormation of multiply charged ions is shown to contribute a significant fraction of the total ionization by high energy electrons, and multiple ionization is almost always followed by charge‐separation reactions. Triple ionization and subsequent dissociations can be well characterized by the electron‐three ion coincidence technique. Results obtained using this new technique are compared with computer simulations of the dissociations of OCS3+and SO3+2, and the initial momenta and relátive angles of all three fragments are thereby determined. Triply charged benzene ions are shown to undergo many competing charge‐separation rea

ISSN:0951-4198    

DOI:10.1002/rcm.1290030606

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractBy introducing an Einzel lens in the field‐free region of a straight time‐of‐flight mass spectrometer, secondary ions of large mass can be detected more efficiently in plasma‐desorption mass spectrometry. This procedure compensates for the large radial velocities of large molecular ions recently observed experimentally. It is shown that large molecular ions like those of lysozyme can now be detected more efficiently, and larger molecular ions than observed before in plasma‐desorption mass spectrometry (like those of bovine ovalbumin, mol. wt 45 000) can now b

ISSN:0951-4198    

DOI:10.1002/rcm.1290030607

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractA strategy for sequencing peptides using the mono‐ and dilithiated quasimolecular ions is proposed. Low energy collision‐induced dissociation (CID) of the monolithiated species produced primarily [An+LiH]+and [Bn+H+OLi]+ions while that of the dilithiated species produced [An+LiH]+and [Yn+Li+H]+ions. The precursor parent ion in the monolithiated adduct is proposed to be a mixture of lithiated neutral peptide (1) and protonated lithium salt (2). Mechanisms for the formation of the [An+LiH]+and [Yn+Li+H]+ions are proposed. Four peptides of known composition but unknown sequence were successfully sequenced using the combined data from the CID spectra of the mono‐ and dilithia

ISSN:0951-4198    

DOI:10.1002/rcm.1290030608

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

Abstract2‐Acylcyclohexane‐1,3‐diones and their 4‐hydroxy analogues were analysed by gas chromatography/mass spectrometry. Fragmentation pathways for the formation of diagnostic ions are su

ISSN:0951-4198    

DOI:10.1002/rcm.1290030609

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

摘要:

AbstractFast‐atom bombardment, thermal ionization and inductively coupled plasma mass spectrometry are contrasted in comparative measurements of64Zn/67Zn isotope ratios on samples isolated in the course of a human mineral‐nutrition experiment. The data are evaluated with reference to the precision normally required in enriched stable‐isotope mineral‐nutrition studies, and the convenience of the mass spectrometric techniques is also c

ISSN:0951-4198    

DOI:10.1002/rcm.1290030610

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY

ISSN:0951-4198    

DOI:10.1002/rcm.1290030612

出版商:Heyden&Son Limited    

年代:1989

数据来源: WILEY