摘要:

AbstractThermal degradation ofO‐acyl oximes under electron impact ionization (EI) conditions has been examined. The EI mass spectra gave fragment ions originating from thermal degradation, as well as molecular ions M+·and normal fragment ions due to unimolecular decomposition of the M+·ions. The fragment ions due to thermal degradation ofO‐acyl oximes were identified by using fast‐atom bombardment (FAB) mass spectrometry with a liquid matrix together with the collision‐induced dissociation (CID) technique. While the FAB mass spectra ofO‐acyl oximes gave, preferentially, M+·ions together with some characteristic fragment ions, as well as the molecular related ions [M+H]+and [M−H]+, the spectra showed little evidence of the fragment ions which may originate from thermal degradation, under EI conditions. The CID spectra of selected M+·ions formed by electron impact also showed little of such fragment ions. The thermal degradation was directly confirmed by measuring the FAB mass spectra ofO‐acyl oximes that had been heated in a s

ISSN:0951-4198    

DOI:10.1002/rcm.1290091102

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractFrozen solutions of a cryoprotector, glycerol, in water were studied by low temperature fast‐atom bombardment mass spectrometry in the temperature range from − 196° to 0°C. Strong dependence of the mass spectral pattern on the water‐glycerol ratio and temperature of the sample was observed. The evolution of mass spectra of the frozen 2000:1 water‐glycerol mixture with increase of the sample temperature is reproducible: in the lower portion of the temperature range (−196° to −120°C) the spectra contain a set of cluster ions, (H2O)nH+, (n= 1–15), characteristic of pure water; then the spectra show a superposition of peaks due to water clusters and glycerol itself, the latter with characteristic changes with temperature rise: degraded ‘peak at every mass’ pattern in the −120° to −80°C range followed by a build‐up of glycerol clusters, GnH+, (n= 1–3) in the −80°C to −55°C range. At approximately −55°C to −50°C a sublimation of water component occurs, detected by [H2O]+·ion, and the remainder of the spectral pattern coincides with that of pure glycerol up to ambient temperature. Mixed water‐glycerol clusters were never observed. An explanation of such spectral behavior is proposed based on ideas about the morphology of the frozen solutions, characterized by water microcrystallites separated by eutectic channels containing cryoprotector. The independent sputtering of the two substances from different dom

ISSN:0951-4198    

DOI:10.1002/rcm.1290091103

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractTime‐of‐flight mass spectrometers are able to cover mass ranges to around a half a million Da. The mass resolution of these instruments has been improved drastically by incorporation of electrostatic mirrors. The ion‐optical solutions enabling these achievements and other promising features are discussed in terms of: First‐ and second‐order space focusing in time for linear drift time‐of‐flight mass spectrometers; velocity focusing by time lag; ion‐packet bunching in post‐source impulse focusing; first‐ and second‐order energy focusing in time, in single‐ and double‐stage homogeneous electrostatic mirrors with normal and oblique ion incidence; gridless designs; perfect time focusing in parabolic potential and axial symmetry; cylindrical ion mirrors and toroidal electrostatic deflectors as time‐of‐flight mass analyzers; three electrostatic sector geometry applied in secondary ion microscopy and four toroidal sector systems for tandem mass spectrometry; poloidal electrostatic sectors. Estimation of time‐of‐flight mass spectrometer performance limits is discussed and the stable as well as the metastable peak shapes fou

ISSN:0951-4198    

DOI:10.1002/rcm.1290091104

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe mass spectra often substituted oxazino[4,3‐a]isoquinolines, two isoquino[2,1‐c][1,3]benzoxazines and seven substituted oxazino[4,3‐a]isoquinolin‐4‐ones were recorded under electron impact ionization. Fragmentations were examined by metastable ion analysis, collision induced dissociation and exact mass measurement. The oxazinoisoquinolines and oxazinoisoquinolin‐4‐ones behaved similarly, although there were a few differences in the fragmentation and especially in the peak intensities. The most important fragmentation began with the opening of the oxazole ring. The substituents affected the fragmentation of the isomeric compounds, whereas the spectra of the stereoisomeric compounds were identical. The two isoquinobenzoxazines differed noticeably from the other compounds in their fragmentation behaviour; the additional phenyl ring prompted entirely new fragmentations unique to t

ISSN:0951-4198    

DOI:10.1002/rcm.1290091105

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractLiquid chromatography (LC), simultaneously coupled with both nuclear magnetic resonance (NMR) and mass spectrometry (MS) ‘on‐line’ is a powerful structural tool and has a potentially vast range of uses within the pharmaceutical industry. Data from a mixture of fluconazole and related triazoles have been obtained from an LC/NMR‐MS system developed ‘in‐house’, demonstrating the power of this novel analyt

ISSN:0951-4198    

DOI:10.1002/rcm.1290091106

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractWe evaluated the precision, accuracy and linearity of three commercial gas chromatography/combustion isotope ratio mass spectrometry (GC/C‐IRMS) instruments in regard to stable carbon isotope ratio measurements of fatty acids with13C enrichment levels ranging from natural abundance to 924‰, in comparison to measurements by conventional gas isotope ratio mass spectrometry (GIRMS). Memory effect was also evaluated with a fatty acid mixture containing methyl myristate and methyl stearate at natural abundance levels of13C but methyl palmitate at13C enrichment levels of 460 or 924‰. At natural abundance, the δ13C values of fatty acids measured by the GC/C‐IRMS instruments were reproducible to within 0.34‰ (range: 0.11‰ to 0.32‰) and accurate to −0.38±0.40‰ (mean difference ± standard deviation; range: −0.03±0.25‰ to −0.84±0.39‰). At enrichment levels of13C (23 to 924‰), the δ13C values were reproducible to within 1.48‰ (range 0.20‰ to 1.00‰) and accurate to −1.11±3.16‰ (range: −1.02±3.23‰ to +4.56±13.42‰). Stable carbon isotope ratio measurements by all three GC/C‐IRMS instruments were found to be linear from −30 to 924‰ (r2>0.9999;p⩽ 0.004) in comparison to those measured by GIRMS. Significant memory effect was found in only one system. Based on our data, the GC/C‐IRMS instruments can provide linear, precise and accurate stable carbon isotope ratio measure

ISSN:0951-4198    

DOI:10.1002/rcm.1290091107

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractLiquid chromatography coupled to atmospheric‐pressure chemical ionization mass spectrometry and tandem mass spectrometry (MS/MS) methods for the determination and quantification of four quinolone antibiotics were adapted from a published procedure for liquid‐liquid extraction from catfish muscle and high‐performance liquid chromatographic analysis. In‐source collision‐induced dissociation was used to optimize fragmentation to produce mass spectra consisting of the protonated molecule and two characteristic fragment ions of nearly equal intensity. Selected ion monitoring of three ions per quinolone yielded sensitive detection in catfish muscle extracts (estimated instrumental detection limits 0.8‐1.7 ppb). The intensity ratios were used to confirm the presence of three of the quinolones based on the accurate agreement (⩽10% deviation) between ratios derived from fortified catfish extracts and those from standard quinolones. MS/MS was used to increase the specificity and sensitivity of analysis. Scans using constant neural loss (CNL) of 18 mass units gave a sensitive response for the quinolones suggesting that CNL scans may be applicable to multiresidue screening for unknown quinolones. MS/MS with multiple reaction monitoring of the [MH18]+transition for each quinolone yielded the highest sensitivity analysis in catfish extracts (estimated instrumental detection limits

ISSN:0951-4198    

DOI:10.1002/rcm.1290091108

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractWe propose a new method for the quantitative determination of carbon dioxide released by a biological microgenerator: a suspension of human polymorphonuclear leukocytes (PMNL). This method is based on the reverse isotope dilution analysis by gas chromatography/isotope ratio mass spectrometry of13CO2released by PMNL in a controlled isotope abundance atmosphere containing 3% CO2.13CO2release is effective after PMNL stimulation in the presence of [13C]glucose, labeled on positions 1, 2 or 6. The validation of this method is carried out by the measurement of the isotope ratio13CO2/12CO2using known amounts of [13C]sodium hydrogen carbonate and the comparison with theoretical isotope abundances derived from various CO2equilibria. Complete release of CO2is achieved by the acidification of the medium. This method requires only few cells, displays high sensitivity and specificity and can be applied to the analysis of large series of samples using an automatic sample injector. In addition, this method can also be applied to other types of biological microgenerators of carbon dioxide.

ISSN:0951-4198    

DOI:10.1002/rcm.1290091109

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe potential of matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI)(I‐TOF) mass spectrometry for use in the identification of human chorionic gonadotropin (hCG) seized by law enforcement agencies is investigated. Analysis of untreated hCG revealed signals corresponding to the molecular ions of the intact hCG heterodimer and both its non‐covalently linked subunits. Unfortunately, due to carbohydrate heterogeneity, the peaks are broad which makes accurate mass assignment, and consequently identification, difficult. Peptide mapping by MALDI‐TOF following‐tryptic digestion gave sequence coverage of 59% and 52% for the α and b̃‐subunits respectively. Nevertheless, the tryptic map was considered to provide unambiguous identification of hCG. This was confirmed by searching peptide‐mass databases with the experimentally determined masses. Our data suggest that peptide mapping by proteolytic digestion followed by MALDI‐TOF mass spectrometry is a suitable analytical technique for the identification of hCG seized by

ISSN:0951-4198    

DOI:10.1002/rcm.1290091110

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY

摘要:

AbstractThe separation of trace impurities in cimetidine drug substance by high pressure liquid chromatography (HPLC) showed a series of minor components. These were analysed using an on‐line electrospray source connected to a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. Working typically with a resolution of 10 000–20 000 accurate mass measurement of the components confirmed their empirical formulae to generally better than 5 ppm accuracy. This work shows that the combination of conventional analytical HPLC using 4.6 mm columns with a low flow rate electrospray source interfaced to an FT‐ICR mass spectrometer enables structural information to be obtained on low levels of low mass com

ISSN:0951-4198    

DOI:10.1002/rcm.1290091111

出版商:Heyden&Son Limited    

年代:1995

数据来源: WILEY