摘要:

AbstractThe experimental verification of predictions of a new simulation model of quadrupole mass filters is presented. Computer calculations show that the transmission of the prefilter‐QMS system is periodical as a function of the prefilter length. The periodicity of the transmission is independent of the mass number of ions of equal velocity. Experimental proof of the simulation has been produced for low mass numbers and a more difficult procedure is required for higher masses (m/z>100). This is realized with a closed ion source and tandem quadrupole mass spectrometer arrangement. Experimental results prove the mass‐independent behaviour predicted by the mo

ISSN:0951-4198    

DOI:10.1002/rcm.1290090802

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractMatrix‐assisted laser desorption/ionization (MALDI) and fast‐atom bombardment (FAB) mass spectrometry experiments were applied to the study of the early stages of the oligomerization reaction of dopamine with mushroom tyrosinase. Ultrafiltration was employed to remove the enzyme at various reaction times, to prevent possible attachment of the protein to the highly reactive intermediates. Two sets of five samples each, obtained at different reaction times, in one case immediately lyophilized and in the other left to react under an oxygen stream for 24 h before lyophilization, were compared. FAB showed the presence of various species and of these, that atm/z305 increased in abundance with reaction time in the immediately lyophilized set of samples only. Accurate mass measurements and tandem mass spectrometric experiments indicated the structure of a dopamine protonated dimer for this ion. MALDI measurements showed that all samples were composed of clusters of oligomers differing in degree of oligomerization. Oligomerization increases with reaction time, resulting in the formation of species at 2643–2911 Da. These clusters in turn were formed of species with a different degree of oxidation, detected in both sets of sa

ISSN:0951-4198    

DOI:10.1002/rcm.1290090803

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractMass spectrometric methodologies which use electrospray ionization (ESI) for oligosaccharide structural determination and which are linked to classical procedures, such as reductive amination, have been established. Several derivatives of a model oligosaccharide were prepared and their ionization efficiencies in electrospray ionization (ESI) and fast‐atom bombardment (FAB) mass spectrometry were investigated. The trimethyl‐(p‐aminophenyl)ammonium (TMAPA) derivatives showed extremely high sensitivity in positive‐ion ESI–MS and gave Y‐ and Z‐series sequence ions by ESI tandem mass spectromety (MS/MS). This study suggests that TMAPA‐derivatized oligosaccharides used in ESI‐MS and ESI‐MS/MS would be effective for structural characterization of oligosaccharides that are available only in

ISSN:0951-4198    

DOI:10.1002/rcm.1290090804

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractA new approach, bio‐affinity characterization mass spectrometry (BACMS), aimed at providing a more rapid, sensitive and potentially more flexible alternative to techniques presently employed for the characterization of noncovalent interactions in mixtures, such as would be encountered in combinatorial chemistry, is presented. BACMS avoids some of the difficulties and potential artifacts associated with affinity chromatography since the noncovalent associations occur in solution; thus, BACMS avoids the requirement of solid support media and the development of non‐interfering linker species. This paper describes the conceptual basis for the methodology and its potential use in applications which include the screening of high affinity ligands in support of new drug development. BACMS exploits new Fourier‐transform ion cyclotron resonance (FTICR) mass spectrometry technologies which, when coupled to electrospray ionization (ESI), allow the investigation of specific noncovalent complexes formed in solution. BACMS utilizes the well‐known attributes of FTICR, such as the high resolution mass analysis and (MS)n(n⩾ 2) capabilities; however, it is even more directly a result of recently developed techniques involving quadrupolar excitation, such as selected‐ion accumulation. These tools are demonstrated and the results illustrate the extraordinary sensitivity achievable (solution concentrations of 1 × 10−9M without the use of separations prior to ESI). Thus, the new capabilities demonstrated here, in conjunction with ESI, will be useful for the investigation of very low relative concentration noncovalent association directly from solution, and promote a faster alternative for combinatorial mixture screenin

ISSN:0951-4198    

DOI:10.1002/rcm.1290090805

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe electron impact mass spectra of some diastereomeric dialkyl tartrates and isopropylidine derivatives of dimethyl tartrate show diagnostic differences in the relative abundances of some ions. The differences have been explained based on preferred conformations of these isomers. The configuration of the carbomethoxy groups has been correlated with the configuration of carbomethoxy groups in dimethyl maleate and fumarate. The interaction between the two carbomethoxy groups is relatively larger in conformations where there is a gauche interaction between them. The results could also be correlated with the solution phase conformations of these compounds reported in the literature using nuclear magnetic resonance techniques. The difference, which is small in diastereomeric dimethyl tartrates, is very reproducible and has been confirmed using six different mass spectrometers.

ISSN:0951-4198    

DOI:10.1002/rcm.1290090806

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractA gas chromatography/negative‐ion chemical ionization mass spectrometry method is presented to measure the isotopic enrichment of multiple serine and glycine isotopomers. The amino acidN‐heptafluorobutyryl n‐propyl ester derivatives were used. The method had good analytical linearity between 10 and 800 μg mL−1and both precision and accuracy were 5% for plasma amino acids. Sensitivity permitted analysis of 100 pg amino acid on column. The method was applied to metabolic studies of the serine to glycine interconversion in humans. (α‐15N)serine and (1,2‐13C2)glycine were given as a single intravenous bolus to six healthy male subjects. Plasma concentration of glycine and serine were determined after addition of (α‐15N,1,2,3‐13C3) serine and (α‐15N,1,2‐13C2)glycine as internal standards to 500 μL of plasma. Since glycine and serine are rapidly interconverted by hepatic serine hydroxymethyl transferase, the resultant tracer spectrum requires deconvolution of the enrichment of four isotopomers of each amino acid. Deconvolution of the ion abundance ratios to yield tracer‐to‐tracee ratios for each isotopomer was done using Brau

ISSN:0951-4198    

DOI:10.1002/rcm.1290090807

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractFifty saponin components of Quil A, a commercially available extract from the bark of the South American treeQuillaja saponariaMolina, were partially structurally characterised. The molecular weights were determined by fast‐atom bombardment mass spectrometry. The glycosyl and elemental composition of all the saponins was determined by applying our recently developed method, monomer mapping, consisting of a computer program and accurate mass measurements. Support for the presumed identity of the aglycone, i.e. quillaic acid, was found in the accurate mass determination,1H NMR measurement and chemical reactions. The saponin composition of Quil A was shown to consist of pairs. Within the 3‐O bound glycosyl moiety of a pair there was a structural difference: a pentose and rhamnose were interchanged. Structural differences between different pairs were located in the 28‐O bound glycosyl moiety. A structural element, unknown to date and of which the elemental composition was deduced to be C8H12O5, was found in the 28‐O bound glycosyl moiety of several s

ISSN:0951-4198    

DOI:10.1002/rcm.1290090808

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe detection limits of a series of small peptides derivatized with 4‐aminonaphthalenesulphonic acid have been determined using a magnetic sector mass spectrometer operated in the negative‐ion mode. The instrument (AutoSpec‐QFPD) is equipped with an electrospray ion source and both array and point detectors. Detection limits when using the array detector were on the sub‐femtomole level at a mass resolution of 2000 (full width half maximum height). Cone‐voltage and linked‐scan collision‐induced dissociation spectra were recorded using both the array and point detectors. When using the array detector, amino acid sequence information could be obtained from as little as 50 fmol of sa

ISSN:0951-4198    

DOI:10.1002/rcm.1290090809

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe [M  H]−ions derived from tetrapeptides generally show two different collision‐induced backbone cleavages which allow the determination of the amino acid sequence of the peptide. The first of these involves the formation of the carboxylate anions of either constituent amino acids or fragment peptides. In the second, amino acids or fragment peptides are eliminated as neutrals. There are a number of residues which undergo characteristic sidechain fragmentations irrespective of their position in the tetrapeptide, e.g. Ser, Thr, Cys, Met, Phe and Tyr. However, there are also some residues which, when situated at the C‐terminal end of the peptide, promote pronounced fragmentation at the C‐terminal position which occurs to the exclusion of the normal backbone cleavages. We conclude that the data obtained from these negative‐ion cleavages are analytically useful, and complement those provided by the cognate positive‐

ISSN:0951-4198    

DOI:10.1002/rcm.1290090810

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractUsing the Knudsen effusion mass spectrometric method, the composition of vapour and the partial pressures of vapour species over melts of the CaOAl2O3system were studied for the temperature range 1833–2033 K. Thermodynamic functions of the CaOAl2O3system were obtained, and the negative deviations from ideal behaviour were illustrated. The dependence of the Gibbs energies of formation of the CaOAl2O3system on temperature and concentration of components was su

ISSN:0951-4198    

DOI:10.1002/rcm.1290090811

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY