ISSN:1076-5174    

DOI:10.1002/jms.1190300602

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractCertain of the “meta‐stable peaks” in mass spectra are abnormally wide. This extra width is shown to be associated with release of kinetic energy during fragmentation. Methods are presented for measuring this energy release and values are given for various transitions in the spectra of aromatic nitro comp

ISSN:1076-5174    

DOI:10.1002/jms.1190300603

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractCollision with neutral molecules is shown to provide a convenient method of adding internal energy to ions in a field‐free drift region of the mass spectrometer. The effects on this process of ion accelerating potential, target gas pressure and identity, and precursor ion internal energy and mass have been investigated to optimize experimental conditions. Such collisions cause ion decompositions whose activation energies cover a broad range; for a particular ion such decompositions can be viewed as its “collisional activation (CA) spectrum.” CA spectra, which can be obtained for each ion in the normal mass spectrum, and which appear to follow the predictions of the quasi equilibrium theory, show many more of the possible unimolecular ion decomposition reactions for an ion than do unimolecular metastables, and thus provide valuable information for ion reaction mechanisms and molecular structure determination. Collisional activation can sometimes yield ion energies which are relatively inaccessible by electron impact. The precursor ion internal energy has a negligible effect on the ion's CA spectrum except for product ions formed through the processes of lowest activation energy. Thus, CA spectra should also be valuable for the characterization of ion struc

ISSN:1076-5174    

DOI:10.1002/jms.1190300604

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractIon‐molecule reactions in a pentaquadrupole mass spectrometer are used to generate cluster ions in which neutral pyridine molecules are bound to a linear polyatomic cation, [OCNCO]+. The dimeric adduct, viz. Py1[OCNCO]+Py2where Py1and Py2represent substituted pyridines, formed upon reaction of mass‐selected [OCNCO]+with a mixture of pyridines, has a loosely bound structure, as suggested by triple stage mass spectrometric (MS3) experiments. Dimeric adducts comprised ofmeta‐ and/orpara‐substituted pyridines (unhindered pyridines) display an excellent linear correlation between the fragment ion abundance ratio ln [Py1[OCNCO]+/Py2[OCNCO]+] and the proton affinity difference of the pyridines. On the assumption that the effective temperature of the [OCNCO]+‐bound dimers is similar to that of the corresponding Cl+‐bound dimers, [OCNCO]+affinities of the substituted pyridines relative to pyridine are estimated to be 3‐MePy 2.3, 4‐MePy 3.2, 3‐EtPy 3.5, 4‐EtPy 4.1, 3,5‐diMePy 4.9 and 3,4‐diMePy 5.6 kcal mol−1(1 kcal = 4.184 kJ). A linear relationship between the relative [OCNCO]+cation affinity and the relative proton affinity (PA) is derived as relative [OCNCO]+affinity (kcal mol−1) = 0.96 ΔPA, using the assumed effective temperature of 555 K. Dimers consisting ofortho‐substituted pyridines display substantial steric effects between theortho‐substituted alkyl group and the central [OCNCO]+cation. A set of gas‐phase steric parameters (Sk) is determined and steric effects are ordered 2‐MePy (‐1.39)<2,5‐diMePy (‐3.02)<2,4‐diMePy (‐3.15)<2,3‐diMePy ( −3.29)<2,6‐diMePy (‐5.09)<2,4,6‐triMe (‐6.13). A greater steric effect is experienced in the [OCNCO]+system than in the corresponding Cl+system, owing to the larger central ion in Py[OCNCO]+Py. Structural and electronic information regarding the bond angles, bond lengths and charge density distributions in [OCNCO]+, Py[OCNCO]+and Py[OCNCO]Py+was obtained fromab initiocalculations. The calculations show that [OCNCO]+is linear with high positive charge densities on the carbon atoms. The calculations also reveal that the Py[OCNCO]+monomer is a planar ion with the nitrogen atom of pyridine bound to a carbon atom of the [OCNCO]+cation, and that the Py[OCNCO]Py+dimer is a symmetrical ion in which the nitrogen atoms on the pyridine molecules bin

ISSN:1076-5174    

DOI:10.1002/jms.1190300605

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn vivomicrodialysis in combination with liquid chromatography/micro‐electrospray mass spectrometry was used to study the metabolism of substance P in rat brain. A microdialysis probe was used both to introduce substance P into the brain and to collect metabolic products. Unilateral infusions of 25 and 50 pmol μl−1substance P, or isotopically labeled [D8‐Phe8] substance P, at flow rates of 0.3 μl min−1, were made through the microdialysis probe implanted in the striatum of anesthetized rats. The metabolic products were analyzed by on‐line mass spectrometry and the results showed that substance P, an 11 amino acid residue polypeptide, was metabolized in the striatum to formN‐terminal fragments 1–9, 1–8 and 1–7;C‐terminal fragments 3–11, 5–11, 6–11, 7–11 and 8–11; and internal fragments 4–8, 6–10 and 7–10. The concentrations of these metabolites in dialysates were measured in order to compare the relative importance of several po

ISSN:1076-5174    

DOI:10.1002/jms.1190300606

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractQuasimolecular peptide [M + H]+ions are generated by matrix‐assisted (2,5‐dihydroxybenzoic acid/D‐fructose) laser desorption/ionization (frequency‐tripled Nd: YAG at 355 nm) from leucine enkephalin, bradykinin, the non‐apeptide Arg–Leu–Cys–Ile–Phe–Ser–Cys–Phe–Arg, angiotensin I, bovine insulin chain B and some of their deuterated derivatives. The ions are cooled and axialized by azimuthal quadrupolar irradiation in the presence of argon collision gas in the ‘source’ compartment of a dual cubic Penning trap. Following ion transfer to the low‐pressure ‘analyzer’ trap, ultrahigh FT‐ICR mass resolving power is obtained for protonated oligopeptide quasimolecular [M + H]+ions: e.g.m/Δm50%≈ 1 500 000 for bradykinin (m/z≈ 1060) after frequency drift correction and 100 000 for insulin B‐chain, in which Δm50%is the magnitude‐mode peak full width at half‐maximum peak height. These results constitute the highest mass resolving power yet demonstrated for internally‐generated MALDI ions at 3 T, and compare favorably with results obtained at much higher‐magnetic field with externally‐generated ions. High mass resolution is important for resolving adducts and chemical modifications of a peptide or protein and (as demonstrated here) for facile determination of the degree of deuteration from an H/D exchange experiment. Limitations to FT‐ICR mass resolving power by Coulombic ion–ion interactions at high ion densit

ISSN:1076-5174    

DOI:10.1002/jms.1190300607

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe gas‐phase ion‐molecule chemistry of exohedrally bound C60Rh+with CH3X, C6H5X (X = Cl, Br, and I) and CH2I2is studied using Fourier transform ion cyclotron resonance mass spectrometry. Reactions with CH3I and CH2I2yield the buckminsterfullerene derivatives, C60CH3+and C60CH2+, respectively. Energy resolved collisional activation experiments on these two product ions indicate that the methylene group is more strongly bound to C60than the methyl group. This is consistent with methylene being bound by two carbon‐carbon bonds to C60, while methyl is bound by a single carbon‐carbon bond. Unlike CH3I, CH3Cl and CH3Br react with C60Rh+in a stepwise fashion to yield C60Rh(CH2)n+(n= 1 − 3). Interestingly, C60Rh(CH2)2,3+are shown to be isomers of C60RhX+(X = ethene, propene), possibly with a carbon‐carbon bond formed with C60. Products containing more than three CH2moieties were not observed. Reactions of C60Rh+with C6H5X(X = Cl, Br, and I) yield C60Rh(C6H4)n+(n= 1, 2), in a stepwise fashion via losses of HX. C60Rh(C6H4)2+is unreactive with C6H5X. Again, indirect evidence for CC bond formation to C60is obtained. Consistent with previous observations on C60Fe+C60Co+, the Rh+–C60bond energy is found to fall between those of Rh+–propene and Rh+–benzene, due to the alk

ISSN:1076-5174    

DOI:10.1002/jms.1190300608

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractSpace‐charge effects appear to be key in understanding ion‐transport processes in plasma‐source mass spectrometry. Both theoretical calculations and experimental measurements demonstrate that space charge influences ion transport between the plasma source and mass analyzer. In a theoretical analysis, both drift space and accelerating space in the interface have been considered and preliminary conclusions have been drawn concerning space‐charge repulsion and ion‐beam divergence in those regions. In the experimental work, spatial patterns of sample deposition on the third stage vacuum orifice plate were recorded while using a microwave plasma source. To measure these patterns, a stainless‐steel target was used to cover the orifice and both x‐ray fluorescence microanalysis and scanning electron microscopy (SEM) were used to examine the sample material deposited on it. The resulting spatial maps show that analyte deposition is somewhat element‐dependent in a way that is correlated with analyte atomic mass. These findings can be explained on the basis of spac

ISSN:1076-5174    

DOI:10.1002/jms.1190300609

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractA procedure which utilizes the specificity of tandem mass spectrometry was developed for the simultaneous quantification of fluphenazine and its stable isotopomer, [2H4] fluphenazine, in 1 ml plasma samples, after low oral doses of this antipsychotic agent. The unlabeled and the deuterium labeled‐drug were isolated by a selective extraction procedure, derivatized and analyzed under electron impact ionization via the direct insertion probe of a tandem mass spectrometer. Selected reaction monitoring of the low‐energy collision‐induced dissociation of analogous major fragment ions to their respective product ions conferred the necessary specificity to allow direct analysis of plasma extracts without the need for a chromatographic separation step. Calibration graphs constructed from spiked blank plasma were linear over the range 25–1000 pg ml−1for each isotopomer, with an overall coefficient of variation of 4.82% and 4.72% for fluphenazine and [2H4] fluphenazine, respectively. The limit of detection was 5 pg ml−1when 1 ml of plasma was used. The described procedure provided sufficient sensitivity and selectivity such that plasma concentrations of fluphenazine and [2H4] fluphenazine could be followed in schizophrenic patients for 24 h after the simultaneous administration of single oral doses that contain 5 mg each of fluphenazine dihydrochloride and its deuterated isotopomer, [2H4] fluphenazine dihydrochloride. Endogeneous plasma constituents and known metabolites of fluphenazine did not interfere in the assay. Virtually superimposable plasma concentration versus time profiles were obtained, demonstrating that the deuterated isotopomer has no significant isot

ISSN:1076-5174    

DOI:10.1002/jms.1190300610

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe use of both pneumatically‐assisted ionspray (IS) and thermospray (TS) in liquid chromatography/tandem mass spectrometry (LC/MS/MS) for the determination of the biotransformation pathways of zanoterone in humans is described. After administration of a single oral dose of [14C] zanoterone, 16% of the dose was excreted as four metabolites in urine. Initially TS LC‐MS/MS analysis indicated the presence of monohydroxylated metabolites; however, their high‐performance liquid chromatographic (HPLC) retention times indicated more polar structures. These conflicting results led to IS experiments, in which abundant molecular ions were obtained for all four metabolites, identifying them as either glucuronide or sulfate conjugates. A contour plot of the data from an IS neutral loss experiment revealed the presence of a minor metabolite not observed in either HPLC–flow scintillation or TS LC‐MS experiments. These data demonstrate the advantages of IS LC‐MS/MS for the analysis of drug

ISSN:1076-5174    

DOI:10.1002/jms.1190300611

出版商:John Wiley&Sons, Ltd.    

年代:1995

数据来源: WILEY