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  • Analytical Chemistry and Spectroscopy  (7,173)
  • 2000-2004  (101)
  • 1990-1994  (7,072)
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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 474-478 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Solid-phase extraction, on-line derivatization, and measurement by ion trap mass spectrometry (ITD-MS) were used to investigate the biological degradation of pharmaceutical residues (clofibric acid, ibuprofen, diclofenac). The results of the single steps of sample pretreatment and analytical determination are reported. MS/MS measurements were performed on an ITD-MS by selecting collision induced dissociation of the molecular ions (M+) as parent ions to defined daughter ions. A pilot sewage plant and biofilm reactors operating under oxic and anoxic conditions were run as model systems with synthetic sewage water containing 10 to 50 mg/L dissolved organic carbon (DOC) and pharmaceuticals in concentrations of 10 μg/L. Clofibric acid displayed its persistent character in all cases. The pilot sewage plant and the oxic biofilm reactor showed comparable results for diclofenac and ibuprofen, which both were partly degraded. These results can explain the occurrence of these substances in sewage effluents and in the aquatic environment. A high degree of degradation was found especially for ibuprofen in the oxic biofilm reactor, which was attributed to adaptation of the biofilm to the residue. Two metabolites of ibuprofen could be identified on the basis of their mass spectra and comparison with literature data, viz. hydroxyibuprofen and carboxyibuprofen.
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 25 (1994), S. 849-854 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Low-wavenumber depolarized Raman spectra (-400 to 400 cm-1) for dioxane, water and glycerol are presented. Stokes and anti-Stokes spectra (-400 to 400 cm-1), are used to define a reduced spectrum, in which the effects of temperature and also flat backgrounds and symmetric central components are removed, without knowledge of these parameters. Comparison with the usual reductions shows that (i) all inelastically scattered photons must be considered as ‘true’ Raman signals, due to processes involving Boson-like excitations, (ii) if central scattering exists, then its intensity also depends on the population factor, (iii) the low-wavenumber Stokes signal is more intense than expected for a factor of n + 1 only, owing to non-linear effects, and (iv) the systematic use of reduced spectra is not essential, and can be hazardous in some cases.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 15 (1992), S. 510-513 
    ISSN: 0935-6304
    Keywords: GC-MS ; Cl ; El ; Flavors ; Cola beverages ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: As part of a study directed at introducing GMP recommendations to the production of non-alcoholic beverages, combined Cl and El mass spectra have been used for the identification of compounds present in extracts of “Cockta” beverage following GC-MS analysis. The amount of useful information present both in the separate Cl and El spectra, and in two of the possible combinations of the spectra, is described.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 681-687 
    ISSN: 0935-6304
    Keywords: Focused microwave assisted extraction ; close microwave-assisted extraction ; DDT ; soil samples ; experimental design ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Optimization of focused microwave (FMW)-assisted extraction of 4,4′-DDE, 4,4′-DDD, and 4,4′-DDT from soil samples was carried out using central composite designs. All the extracts were analyzed with GC/MS and some of them also with GC/AED using columns of different polarities for each of the techniques. The extraction of the analytes was carried out in two ways: with acetic acid as microwave radiation absorbent solvent and n-decane to concentrate the analytes and with reagent water and iso-octane as solvents. In the first case, the influence of the extraction temperature, the extraction time, and the addition of sodium chloride were studied and the optimum conditions for the extraction of 1 g of soil with 5 mL of acetic acid and 2 mL of n-decane were 1.30 mol L-1 sodium chloride at 98°C for 9.3 min. In the second case, the temperature was kept constant (94°C) and the influence of the concentration of sodium chloride and the extraction time were studied. The optimum conditions were 5 mL of a 2.0 mol L-1 sodium chloride together with 2 mL of iso-octane for 15 min. The recoveries obtained by water-FMW extraction were significantly lower than those obtained by the acetic acid-FMW procedure. These last recoveries were in good agreement with those obtained by closed microwave assisted-extraction with acetone-n-hexane as solvent.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 14 (1991), S. 361-362 
    ISSN: 0935-6304
    Keywords: Enantioseparation of α-Pinene ; Chiral mobile phase additive ; Cyclodextrins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 505-507 
    ISSN: 0935-6304
    Keywords: Enantioseparation of monoterpenes ; Cyclodextrins ; Chiral mobile phase additive ; UV-indirect detection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 5 (1991), S. 32-34 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A new ionization technique based on a modification of the conventional plasma-desorption mass spectrometric apparatus is described. An electron avalanche produced by the microchannel plates of a secondary electron multiplier is found to desorb a sufficient amount of (quasi-)molecular ions of non-volatile thermally labile molecules. Spectra of several substances with molecular masses up to 1250 u are presented. The mechanism of electron avalanche desorption is now under investigation.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 5 (1991), S. 276-277 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A straightforward relationship between the average and the monoisotopic masses of peptides (proteins) and oligonucleotides is proposed which allows one to calculate the monoisotopic mass from aknown average mass with a 0.1 u order of precision. The approach offered here can be applied to any type of biopolymer.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 5 (1991), S. 278-282 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Direct comparision of two ionization techniques, 252Cf plasma-desorption and electron-avalanche-desorption, is given in various aspect. signification differences were observed in the low-mass region, and in the spectra of volatile compounds and CsI samples, as well as in the fragmentation pattern of alanilnorleucine. On the other hand, a rather high degree of similarity was obtained in spectra of nitrocellulose and some cyclic depsipeptides, both in typical values of peak width and of the high-mass background character. The conclusion is made, that electron-avalanche desorption is a rather complex process involving various factors.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 8 (1994), S. 906-912 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A method of deriving peptide sequence information using partial acid hydrolysis in combination with accurate mass measurements and immonium ion analysis provided by high-resolution plasma desorption mass spectrometry has been developed. The technique is very simple in terms of the chemistry and involves a short-time (3-30 min) incubation of the peptide in 1N-6N HCl at 100-110°C with subsequent mass spectrometric analysis. Partial acid hydrolysis is found to produce sequence-specific segments, often ladder-like, although not always a complete set. Two application examples of the method are given: the linear peptide bradykinin and desmopressin, a peptide with an internal S—S bond and a non-amino-acid constituent. The technique has proved to be particularly useful in cases where some a priori information on the peptide structure was already known or where the automated Edman degradation technique might yield erratic results or not work at all.
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  • 11
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    X-Ray Spectrometry 19 (1990), S. 275-283 
    ISSN: 0049-8246
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Sub-micron spheres of pure materials prepared by electrohydrodynamic atomization were used to determine experimentally the x-ray distribution function, φ(ρz), for spheres using a dedicated HB501 scanning transmission electron microscope at 100 keV. The materials chosen were W, Pd, Ni, V and Al thin spheres. φ(ρz) was measured experimentally using a tracer technique. The thin film tracers used were Ir, Ag, Cr, Cu and SiO2, respectively. φ(ρz) for the above materials was also calculated using a Monte Carlo trajectory simulation modeled for the tracer technique. The experimental tracer φ(ρz) results show a pronounced scatter, especially for large-diameter spheres. Local variations in the tracer film thicknesses appear to be the reason for such scatter. The trends in the experimental and Monte Carlo results, however, are simple and show a strong dependence on the atomic number of the target material. A general expression for φ(ρz) for thin spheres is presented which fits the experimental tracer results. The Monte Carlo results agree well with the fitted data for elements of low atomic number and/or small-size spheres. For elements of higher atomic number (Pd and W), however, the Monte Carlo φ(ρz) curves peak too early with mass thickness. This problem may be due to inadequacies of the scattering cross-section models used in the analysis.
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 16 (1993), S. 188-191 
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Thermostable WCOT columns ; PLOT columns ; Stainless steel ; Silicon layer for deactivation ; Simulated distillation ; PNA analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A layer of elemental silicon has been deposited on the surface of stainless steel tubing by means of chemical vapor deposition (CVD). Two kinds of capillary column were prepared from the deactivated tubing: cross-linked, silanol-terminated polydime-thylsiloxane wall coated open tubular (WCOT) columns and molecular sieve 13X porous layer open tubular (PLOT) columns. Unlike fused silica capillary columns, stainless steel WCOT and PLOT columns can be operated at temperatures in excess of 400°C. High temperature simulated distillation has been performed successfully with a macro bore WCOT column and rapid PNA (paraffin, naphthene, and aromatic) analysis with a multidimensional gas solid chromatographic (GSC) system using PLOT columns.
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  • 13
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 29 (1994), S. 253-259 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1- and 2-monoacylglycerols and 1,2- and 1,3-diacylglycerols of saturated and unbranched fatty acids with 8, 10, 12, 14, 16 and 18 carbon atoms were synthesized and subsequently derivatized with nicotinic acid chloride hydrochloride. The resulting nicotinoyl derivatives were examined by mass spectrometry in the case of pure substances and as mixtures by gas chromatography/mass spectrometry (GC/MS). From the electron impact mass spectra, differentiation between mono- and diacylglycerols and between the two positional isomers of mono-acylglycerols and diacylglycerols is possible. The molecular masses of the partial acylglycerols and the identities of the bonded fatty acid were also determined. Similarly to the nicotinoyl derivatives of saturated fatty alcohols, the nicotinoyl derivatives of partial acylglycerols produce a fragmentation pattern that reflects every methylene group of the alkyl chains. These results offer rules for the structure elucidation of partially acylated acylglycerols and probably for mixed diacylglycerols by means of GC/MS, which includes the detection of double bonds and methyl branch positions at the fatty acid alkyl chains. The molecular formulae of all the important fragments in the mass spectra of the nicotinoyl derivatives were confirmed by high-resolution mass spectrometry. Their structures and fragmentation pathways are proposed.
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  • 14
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 13 (1990), S. 148-148 
    ISSN: 0935-6304
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 15
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 25 (1990), S. 517-521 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass fragmentation behaviour of 3,4-dihydro-1H-2,3-benzothiazine 2,2-dioxides was studied. The rationalizations suggested are supported by accurate mass measurements, metastable evidence and deuterium labelling.
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  • 16
    Electronic Resource
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    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 21 (1990), S. 769-779 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Recent experimental and theoretical developments in spontaneous hyper-Raman spectroscopy (HRS) are reported. The scope of the general review of HRS presented summarizes the results of this non-linear scattering technique during the past 10 years. In particular, those aspects of HRS studies which allow novel observations as compared with other spectroscopic techniques are emphasized. HRS investigations of crystals, liquids and surface and electronic resonance enhancement are highlighted.
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  • 17
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    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. S3 
    ISSN: 0749-1581
    Keywords: Transient NOE experiments ; Synchronous nutation experiments ; NAD stack interactions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cross-relaxation interactions between the nicotinamide moiety and the adenine moiety of NAD in D2O solution were unambiguously revealed by steady-state NOE experiments, transient NOE experiments and synchronous nutation experiments. The experimental results, which allow a concise description in terms of auto-relaxation and cross-relaxation, are interpreted as the result of a stacking interaction. Studies of 13C relaxation and investigations on ternary mixtures with 6-methylpurine give evidence for an inter- rather than intra-molecular stack interaction, at least in the NMR concentration range.
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  • 18
    Electronic Resource
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    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 29 (1991), S. 580-586 
    ISSN: 0749-1581
    Keywords: [Lys8]-vasopressin homologues ; NMR assignments in peptides ; Conformational analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The assignment of proton NMR signals and the conformational analysis of N-(Gly)-[Lys8]-vasopressin and N-(Gly—Gly—Gly)—[Lys8]-vasopressin in dimethyl sulfoxide solution by means of one- and two-dimensional NMR techniques are presented. Dihedral angles obtained from 3J (HN—C—α-H) vicinal couplings, intramolecular distances estimated from nuclear Overhauser enhancements (NOEs) and two-dimensional experiments in the rotating frame (ROESY), as well as temperature dependences of the amide protons, suggest a more or less rigid ring conformation with an inverse γ-turn for both cyclic peptides.
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  • 19
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    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 30 (1992), S. 387-392 
    ISSN: 0749-1581
    Keywords: Vasopressins ; Peptide dynamics in solution ; NMR relaxation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The dynamic behaviour of [Lys8]-vasopressin derivatives, especially of N-Gly-Gly-Gly-[Lys8]-vasopressin in solution, was investigated by NMR relaxation studies. One can derive a set of dynamics data which describe the molecular tumbling in solution from 13C spin-lattice relaxation times, T1, spin-spin relaxation times, T2, and heteronuclear nuclear Overhauser enhancements (NOE). Two different approaches, the scheme proposed by Jardetzky and co-workers and the ‘model-free’ approximation of Lipari and Szabo, are used to analyse the dynamics and a comparison of the corresponding data is given. In addition to a mobility of 108-109 s-1, we observe a faster mobility of the order of 109-1010 s-1 in addition to slow dynamic contributions. The latter can be associated by means of T1, measurements with a motion involving the S—S linkage in the vasopressin. Some additional motion is described as the overall mobility of an associate. The results from 13C relaxation were corroborated by 15N T1 measurements, performed at the 15N natural abundance level by an INEPT-reverse INEPT method, and by 15N NOE investigations.
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  • 20
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    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 19 (1990), S. 13-26 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The determination of the amino acid composition and sequence of a peptide, using both conventional and tandem fast atom bombardment mass spectrometry, is presented. First a list of potential empirical formulae is generated using the accurate mass and isotopic peak intensity ratios from the molecular ion cluster. The formulae are mathematically analyzed to ensure that they correspond to linear peptides composed of 19 common amino acids. Then using the ions below m/z 160 Da, which are characteristic of the amino acid content of the peptide, the formulae are decomposed into possible amino acid compositions. From each composition sequences are generated and their predicted fragment ions are compared to ions present in the mass spectrum. A score based on the intensities and the occurrence of consecutive sequence fragments is calculated. Finally sequences with the ten highest scores are retained. Analyses performed on typical peptides with molecular weights below 1500 Da indicate that identification can generally be achieved using this approach.
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  • 21
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: SERS and SERRS spectra in aqueous silver sol for Ru(II) polypyridine complexes with 2,2′-bipyridine (bpy) and 1,1′-biisoquinoline (Q) [Ru(bpy)2+3, RuQ2+3, Ru(bpy)2Q2+ and Ru(bpy)Q2+2] were observed with 457.9, 488.0, 514.5 and 632.8 nm excitation. The vibrational modes of the conjugated ring system in the 1600-1400 cm-1 region are enhanced by the resonance effect. Some bands in the SERS spectra of the four complexes show remarkably high intensities with longer wavelength excitation. This may be explained by surface selection rules.
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  • 22
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ion-molecule reactions of allyl bromide with the molecular ion of allyl bromide and with its major fragment, the allyl ion, yield the C6H7+ and C6H9+ ions. The structure of these product ions was explored by means of photofragmentation with laser light in the 10 μm region and by proton transfer reaction to selected reagents. These product ions were also formed by other reactions and their reactivities compared. In both cases the presence of at least two populations is demonstrated. For C6H9+ these two populations are initially present, whereas for C6H7+ an isomer is formed by the infrared light before the loss of H2. When this ion is produced by photofragmentation of C6H7+, at least one third, stable isomer is formed. Two isomers of C6H5+ are formed in the photofragmentation of C6H7+, but only one form photofragments further by loss of C2H2. The use of non-linear least-squares fitting does not allow definite conclusions to be drawn concerning the kinetics of the consecutive photofragmentations.
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  • 23
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    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 17 (1994), S. 563-564 
    ISSN: 0935-6304
    Keywords: Capillary electrophoresis ; Electrolysis ; Electrolytic effect ; pH Variation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 24
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    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 25 (1990), S. 260-264 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A field desorption mass spectrometric method is proposed for the analysis of mixtures of surfactant and inorganic salts. Different compounds in the mixture are determined with different heating currents and distinguished on the basis of the exterior character of the mass spectrum. The effectiveness of the method is demonstrated with known mixtures of surfactants and inorganic salts. Two unknown additives for electric tin plating were tested with the method.
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  • 25
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Trifluoroacetyl-n-butyl ester derivatives of deuterium-labelled valine, leucine, isoleucine and phenylulanine were analysed by the isotope dilution technique and gas chromatography/mass spectrometry (GC/MS). Selected ion retrieval and peak-area integration were applied. The conditions adopted gave good separations with a short experimental time and high intensity. Ratios of the total isotopic abundance and metabolic kinetic curves were obtained. The regression coefficient of the standard dilution curve was 0.99 and the relative standard deviation was 0.3%. The stabilities of the amino acid derivatives were also tested.
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  • 26
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    Biological Mass Spectrometry 19 (1990), S. 782-786 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proteolytic digests of human antithrombin III (ATIII) have been analyzed by a combination of reversed-phase high-performance liquid chromatography and fast atom bombardment (FAB) mass spectrometry for disulfidecontaining peptides which are diagnostic for disulfide linkages in ATIII. These results indicate that disulfide bonds join Cys 8 and Cys 128, Cys 21 and Cys 95, and Cys 247 and Cys 430. In addition, these results demonstrate that systematic searches of the amino acid sequence of a large protein for segments with molecular weights matching FAB mass spectral information is a viable method for identifying peptides independent of the specificity of the enzyme used to fragment the protein.
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  • 27
    ISSN: 0935-6304
    Keywords: Gas Chromatography ; Stationary phase ; Liquid crystalline crown ether ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new kind of side chain liquid crystalline polysiloxane containing a crown ether with a longer spacer (PSC-11) has been prepared and coated on a fused silica capillary column. The main chroma-tographic characteristics including efficiency, polarity, and selectivity have been examined. The phase exhibits the retention properties of both liquid crystal and crown ether stationary phases and possesses higher efficiency and better selectivity than PSC-3, which has a shorter spacer between the main polysiloxane chain and liquid crystalline side chain.
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  • 28
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    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 6 (1992), S. 671-678 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Measurements of kinetic energy distributions of molecular ions ejected into an extraction field by matrix-assisted laser desorpton re reported. The measurements were made in a time-of-flight mass spectrmeter with an electrostatic mirror by measuring the reflected signal as a function of the difference between the accelerating voltage and the voltage applied t the mirror. The molecular ions ere found to have less kinetic energy than the extraction field alone would normally provide, i.e. we observed an nergy deficit. Under conditons typical for a matrix-assisted laser desrptio experiment, the deficit is about 24 eV for oleclar ions of insulin. The size of the deficit increases with the intensity of the molecular ion signal, and the molecular weight of the protein; t is also larger for negative molecular ions than for positive molecular ions.
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  • 29
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    Organic Magnetic Resonance 31 (1993), S. 194-199 
    ISSN: 0749-1581
    Keywords: 2D NMR (COSY, ROESY, HETCOR, FLOCK) ; Conformation ; Computer modeling ; Molecular dynamics simulation ; Yuanhuacin ; Thymelaeaceae ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereochemical assignments of yuanhuacin were performed through two-dimensional COSY, ROESY, 1H and 13C shift correlation spectroscopy (HETCOR and FLOCK), and ambiguous assignments were resolved through molecular modeling comparisons. This combination of techniques is applicable for the assignment of 1H and 13C chemical shifts of polycyclic compounds containing high percentages of quaternary carbons.
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  • 30
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    Journal of Chemometrics 4 (1990), S. 323-330 
    ISSN: 0886-9383
    Keywords: Target factor analysis ; Spectrophotometry ; Amino acids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The UV spectra of mixture solutions consisting of tyrosine, tryptophane, phenylalanine, cystine, histidine and 3,4-dihydroxyl phenylalanine have been measured. The numbers, identities and concentrations of the amino acids in the mixtures have been determined successfully using target factor analysis. The effects of the wavelength range and the selected sampling interval on the results are discussed. Twenty-five synthetic mixture samples have been analysed successfully. The average recoveries are 98.9 for Tyr, 96.5 for Trp, 105.6 for Phe, 98.1 for Cys, 98.9 for His and 106.4 for Di-phe. The results obtained are in good agreement with those obtained by the Kalman filter method.
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    Rapid Communications in Mass Spectrometry 8 (1994), S. 481-483 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A method for obtaining fast-atom bombardment mass spectra of samples on paper is described in which a scrap trimmed from the paper of interest is adhered to the FAB probe tip with a strip of double-faced adhesive tape. After addition of suitable matrix (e.g. glycerol or thioglycerol) to the scrap, the probe is introduced into the mass spectrometer to obtain mass spectra in the usual manner. The method is demonstrated by analysing some paper containing hexadecyltrimethylammonium bromide, sodium dodecylbenzene sulfonate and vanillic acid. The method is also used to characterize paper chromatographic spots, by which the fractions of a mixture of three amino acids (L-glutamic acid, L-proline and L-valine) separated by paper chromatography are easily determined. The detection limit of the method is well below 10 ng with respect to hexadecyltrimethylammonium bromide.
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  • 32
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    Rapid Communications in Mass Spectrometry 8 (1994), S. 735-736 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Phthalates (dimethyl, diethyl, dibutyl, diallyl and dinonyl) and p-toluenesulfonates (methyl and ethyl) have been investigated as matrices for the fast-atom bombardment mass spectrometric analysis of fullerenes for the first time. Compared with spectra obtained using 3-nitrobenzyl alcohol and 2-nitrophenyl octylether as matrices, the fast-atom bombardment mass spectra of fullerenes with the two classes of compounds listed above as matrices are simple and show no fragment ions or adduct ions of fullerenes, and the matrices produce no background interference in the mass range of fullerenes.
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  • 33
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    Journal of Raman Spectroscopy 21 (1990), S. 203-205 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The Fourier deconvolution technique was applied to the analysis of Raman OH stretching spectra in H2O2—H2O mixtures. An intensity decrease and a low-frequency shift of the resolved high-frequency component at 3635 cm-1 was established and can be used in the elucidation of physical models explaining the existence of weakly hydrogen-bonded OH oscillators in liquid water.
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  • 34
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    Journal of Microcolumn Separations 4 (1992), S. 411-417 
    ISSN: 1040-7685
    Keywords: capillary electrophoresis ; superox-coated capillaries ; proteins ; protein digests ; peptides ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fused silica open tubular columns treated with Superox 0.6 and 4 for capillary electrophoresis were evaluated. Excellent separations of proteins were obtained. Column effeiciencies of over 700,000 theoretical plates were achieved for basic proteins. The relative standard deviations (RSDs) in migration times for these proteins were below 1%. Comparisons were made of the electropherograms of α-, β-, γ-, and δ-chymotrypsins. Three different protein digestion reagents were used to produce complex peptide mixtures for analysis: trypsin, chymotrypsin, and pepsin. Each reagent produced a unique mixture of peptides. Capillary electrophoresis was used to elute the peptides, yielding highly efficient and reproducible separations.
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  • 35
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Positive ion fast atom bombardment mass spectrometry of N-diisopropyloxyphosphoryl dipeptides and tripeptides showed a novel cleavage pattern in that only the N-phosphoryl fragment ions gave intense peaks while the C-terminal series of ions was suppressed. The base peak was the N-phosphoryl imino ion responding to the N-terminal residue. These advantages are superior to those of other types of N-protecting groups.
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  • 36
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    Journal of Microcolumn Separations 5 (1993), S. 331-339 
    ISSN: 1040-7685
    Keywords: capillary electrophoresis ; chemiluminescence detection ; sheath flow cuvette ; post-column reaction ; amino acids ; isoluminol thiocarbamyl derivatives ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A post-column reactor was designed for chemiluminescence detection in the capillary electrophoresis separation of isoluminol thiocarbamyl derivatives of amino acids. This system was characterized with respect to hydrogen peroxide concentration and flow rate, surfactant concentration, microperoxidase concentration, and mixing distance. A linear calibration curve (R 〉0.999) was constructed for isoluminol ranging from at least 30 femtomoles to the detection limit of 40 attomoles injected; the dynamic range of the instrument is at least three orders of magnitude. Detection limit for the isoluminol thiocarbamyl derivative of valine was 500 attomoles. The theoretical plate counts for the raw data are typically 1 × 105 for labeled amino acids, and a factor of two better for isoluminol.
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  • 37
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    Biological Mass Spectrometry 27 (1992), S. 428-434 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photofragmentation of an equimolar mixture of cycloheptatriene and [1, Me-13C2]toluene was studied with photons of wavelength 488 nm in order to obtain a direct comparison between the two isomers. The idea was to check the extent to which these photons could be used as a probe to study the fragmentation processes. Whenever feasible, the data were treated by a kinetic scheme and rate constants were obtained by a non-linear regression. It could be shown that the decay of both isomers follows a time behaviour described by two exponential decays. Evidence is presented that the faster decay leads to the benzyl ion. The photofragmentation of the [C7H7]+ ions follows a complex behaviour that can be superimposed by selective ion-molecule reactions.
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  • 38
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    Journal of High Resolution Chromatography 16 (1993), S. 689-692 
    ISSN: 0935-6304
    Keywords: Solid phase microextraction (SPME) ; Headspace analysis ; Headspace solid phase microextraction ; Environmental analysis ; Water analysis ; Solid samples ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The analysis of samples contaminated by organic compounds is an important aspect of environmental monitoring. Because of the complex nature of these samples, isolating target organic compounds from their matrices is a major challenge. A new isolation technique, solid phase microextraction, or SPME, has recently been developed in our laboratory. This technique combines the extraction and concentration processes into one step; a fused silica fiber coated with a polymer is used to extract analytes and transfer them into a GC injector for thermal desorption and analysis. It is simple, rapid, inexpensive, completely solvent-free, and easily automated. To minimize matrix interferences in environmental samples, SPME can be used to extract analytes from the headspace above the sample. The combination of headspace sampling with SPME separates volatile and semi-volatile analytes from non-volatile compounds, thus greatly reducing the interferences from non-target compounds.This paper reports the use of headspace SPME to isolate volatile organic compounds from various matrices such as water, sand, clay, and sludge. By use of the technique, benzene, toluene, ethyl-benzene, and xylene isomers (commonly known as BTEX), and volatile chlorinated compounds can be efficiently isolated from various matrices with good precision and low limits of detection. This study has found that the sensitivity of the method can be greatly improved by the addition of salt to water samples, water to soil samples, or by heating. Headspace SPME can also be used to sample semi-volatile compounds, such as PAHs, from complex matrices.
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  • 39
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    Organic Magnetic Resonance 32 (1994), S. 36-39 
    ISSN: 0749-1581
    Keywords: NQR ; Natural hybrid orbitals ; Halogenated hydrocarbons ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The natural hybrid orbitals of halogen atoms in various halogen-substituted alkanes and benzenes have been calculated by the Fenske-Hall MO SCF method and natural hybrid orbital theory. Four consistent parameters i, s, d and π are derived to describe the nuclear quadrupole coupling constant (QCC) of the halogen isotopes 35Cl, 81Br and 127I, with modification by the asymmetry parameter η. A semi-empirical expression is proposed from a different point of view.
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  • 40
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    Journal of Microcolumn Separations 6 (1994), S. 217-221 
    ISSN: 1040-7685
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have developed a new method to quantitatively determine ionized calcium and total calcium by using high performance capillary electrophoresis (HPCE) with indirect photometric detection. Other cations such as Na+, K+, and Mg+ can also be quantitatively determined. A 70 cm × 50 μm i.d. fused silica capillary was used for the separation. The detection window was located 25 cm from the cathodic end, and the detection wavelength was set at 214 nm. A 100 mM imidazole solution at pH 7.4 (adjusted with 5% H2SO4) containing 0.1% hydroxypropylmethylcellulose (HMC, 4000 centipoise) was used as background electrolyte. Whole serum was injected for 5 s at 15 kV for the determination of ionized calcium. The total calcium levels in a number of human serum samples were determined by HPCE and compared with the NIST reference method (atomic absorption), and the results agree with each other within 95% confidence. Two NIST standards were analyzed by HPCE, and the results fit each other perfectly. The ionized calcium levels in sera by this HPCE method have been compared with those obtained with ion-selective electrode (ISE) method, and the results were lower than those of ISE, which was what we anticipated. The effects of sample temperature and buffer pH were studied.
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  • 41
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    Journal of High Resolution Chromatography 13 (1990), S. 683-688 
    ISSN: 0935-6304
    Keywords: Capillary gas chromatography ; Recycle gas chromatography ; Microvalve ; Connectors ; Band broadening and peak distortion ; Activity ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Sources leading to band broadening and peak distortion have been studied in a capillary column recycle system, based on a commercial microvalve. The ferrule system was a major contributor to band broadening. It was found that the quality of connections is very critical but the internal volume of the valve is not important. The pressure pulses resulting from each switching operation produced some band broadening with substances that had just been transferred through the valve but no adverse effects were noticed when they had travelled some distance into the column. Flow into valve cavities and through tees also produced a drop in efficiency. It is not clear whether this is solely due to problems in column connection or if changes in flow pattern also contribute.The activity of the valve toward polar substances was also assessed. No attempt was made to deactivate valve surfaces. The components of the Grob test mixture were almost unaffected but highly polar and acidic compounds such as nitrophenol showed severe losses. No evidence for catalysis was found.
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  • 42
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    Journal of Raman Spectroscopy 21 (1990), S. 127-131 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The influence on silver colloids of the addition of KCI was directly investigated by means of transmission electron microscopy (TEM). It was found that the particle size increased and the surfaces of the crystal particles of the silver became covered with an overlayer. Additionally, the pattern of aggregation was found to be chain-like. These changes were very different from those caused by adding pyridine. The mechanism affecting the colloid and the intensity of the surface-enhanced Raman scattering signals of adsorbed molecules on adding KCl to silver colloid is discussed.
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  • 43
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    Journal of Raman Spectroscopy 25 (1994), S. 515-520 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectra excited at two laser wavelengths are used to study the damage in self-implanted silicon. Depending on the implantation conditions, a three-layer structure can be constructed: a damaged surface crystalline layer (dsc-Si), an amorphous layer (a-Si) and a damaged interior crystalline layer (dic-Si). Raman spectra can provide the structural details of these layers, together with the Rutherford backscattering-chanelling technique. Examination of the scattering intensities shows that the contribution to the Raman signals from different layers can be distinguished and separated. Further analysis of the Raman data reveals a defect-activated low-frequency band in the dsc-Si layer which is sensitive to the damage and may be used for the characterization of dsc-Si. For totally amorphlzed samples the two Raman spectra excited at 457.9 and 647.1 nm show different scattering intensity ratios for the optical- and acoustic-like phonons. This novel result may indicate a depth-dependent variation of the disordering in the amorphous layer. Quantitative comparison between the calculated and measured Raman scattering intensities provides the scattering efficiency ratios of dsc-Si and a-Si in samples comprising both dsc- and a-Si layers.
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  • 44
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    Biological Mass Spectrometry 27 (1992), S. 991-994 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several approaches have been proposed for the use of mass spectra from collisionally activated dissociation (CAD) to determine the isomeric composition of mass analyzed ions. As originally proposed, measurement at collision gas pressures (≍ 30% transmittance) yielding maximum CAD cross-sections provides improved precision, whereas differential isomeric scattering should not be an appreciable problem, despite earlier warnings. For the C2H4O+· ions from butan-1,3-diol, this CAD method found [CH3CHO+·] = 50 ± 4%, in agreement with values of 44 ± 6 and 45 ± 6% from two methods of neutralization-reionization mass spectrometry, but in contrast with 66 ± 5% from a proposed CAD methodology using high transmittance measurements. The agreement of the three methods also shows that the principle of linear superposition of spectra is applicable to CAD as well as to electron ionization mass spectra.
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  • 45
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    Journal of High Resolution Chromatography 23 (2000), S. 445-448 
    ISSN: 0935-6304
    Keywords: O-Aryl,O-(1-methylthioethylideneamino)phosphates ; retention prediction ; quantitative structure-retention relationship (QSRR) ; reversed-phase HPLC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Using factor analysis and stepwise linear regression methods, two parameters - CMR and ECCR - were selected from eight solute-related structure parameters as the most retention-influencing parameters. The relationships between the retention data (k ´) and the two structure parameters were established for 13 O-aryl,O-(1-methylthioethylideneamino)phosphate compounds under a wide range of experimental conditions. The retention data (k ´) of another seven compounds with similar structures were predicted using these QSRR equations. Good agreement was obtained between the experimental k ´ values and predicted ones.
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  • 46
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Arachidonic acid is oxidized to regioisomeric 5(S)-, 12(S)- and 15(S)-hydroxyeicosatetraenoic acids by the corresponding 5-, 12- and 15-lipoxygenases. These hydroxylated fatty acids can then be incorporated into cellular phos-pholipids. Negative liquid secondary ion tandem mass spectrometry using a high-energy collision regime in a tandem four-sector mass spectrometer was used to characterize regioisomeric hydroxyeicosatetraenoic acids and the corresponding hydroxyeicosatetraenoic phosphatidylcholine species. Collision-induced dissociation (CID) of the [M - H]- negative ion at m/z 319 from the hydroxyeicosatetraenoic acids regioisomers produced some similar product ions, such as m/z 301 [M - H - H2O]- and m/z 257 [M - H - (H2O + CO2)]-. In addition, product ions characteristic of the particular hydroxyeicosatetraenoic acid were formed from α cleavages adjacent to the hydroxyl moieties. Negative liquid secondary ion mass spectrometry of purified hydroxyeicosatetraenoate phosphatidylcholine species gave an ion at m/z 810 [M - CH3] -. CID of the m/z 810 ion gave product ions at m/z 283 and m/z 319, corresponding to stearate at the sn-1 position and hydroxyeicosatetraenoate at the sn-2 position, respectively. From CID of the negative ion at m/z 319 and examination of the product ion spectra, the hydroxyeicosatetraenoate regioisomer present in the phosphatidylcholine could be identified.
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  • 47
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of sulphur with phosphine and phosphite were investigated by low-energy electron impact mass spectrometry and fast atom bombardment mass spectrometry. A previously reported mechanism of the Ph3P-S8 reaction was supported and a possible mechanism for the (PhO)3P-S8 reaction is proposed.
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  • 48
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    Journal of Raman Spectroscopy 24 (1993), S. 753-759 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectra of m-nitrobenzoic acid-diethanolamine single crystal in the wavenumber range 10-3500 cm-1 were recorded at room and liquid nitrogen temperatures. The internal vibrations were assigned. The Raman spectra provide evidence for the formation of hydrogen bonds in the crystal.
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  • 49
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    Journal of Raman Spectroscopy 25 (1994), S. 327-330 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman spectra of a 3-methyl-4-nitropyridine N-oxide crystal were investigated as a function of pressure in a diamond-anvil cell up to 93 kbar at room temperature. The crystal shows successive reversible phase transitions at 8, 20 and 60 kbar. Above 60 kbar, all of the external Raman peaks and most of the internal peaks were found to vanish, and this is interpreted as due to polymerization or a crystalline-to-amorphous phase transition. On decreasing the pressure, this amorphous state persists to about 20 kbar, and then the spectrum can be recovered completely on decreasing the pressure continuously to ambient, Zallen and Slade's vibrational scaling law was successfully checked.
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  • 50
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    Organic Magnetic Resonance 32 (1994), S. 465-467 
    ISSN: 0749-1581
    Keywords: NMR ; Nuclear spin-spin coupling constant ; Hybrid orbital ; Maximum bond order hybrid orbital ; Net atomic charge ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A generalized relationship to describe bond coupling constants is introduced. This expression includes the contributions for hybrid orbitals and the net atomic charges. The resulting expression provides an excellent description of directly bonded C—H coupling constants. This equation is suitable both for hydrocarbons and for molecules with —I+ and —I- substituents.
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    Biological Mass Spectrometry 25 (1990), S. 435-437 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 52
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Structures of the fatty acid characterizing the various components of A40926 were determined by gas chromatography/mass spectrometry on the methyl esters obtained by methanolysis of the complex. The results confirm the residues previously assigned to Factor A (n-Undecanoic acid) and B (10-methyl-undecanoic acid) and establish the residues of Factor A1(9-methyl-decanoic acid), B1 (n-dodecanoic acid), RS1 (8-methyl-nonanoic acid), RS2 (n-decanoic acid), and RS3 (n-tridecanoic acid). As the actinomadura species contain in their mycelia large quantities of C15-C17 fatty acid residues as membrane phospholipids, these mycelia were saponified and the fatty acids obtained were analyzed as above. There is a close correlation beterrn the fatty acid content of A40923 complex and that of longer homologues in the producer mycelia.
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  • 53
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    Organic Magnetic Resonance 30 (1992), S. 683-685 
    ISSN: 0749-1581
    Keywords: 1H ; 13C ; 15N NMR ; spectra Bradykinin derivatives ; COSY ; TOCSY and ROESY ; Inverse correlation experiments ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complete assignment of the 1H, 13C and 15N spectra of bradykinin derivatives is presented. The proton assignments were performed using COSY, TOCSY and ROESY experiments, whereas the heteronuclei were assigned using inverse correlation experiments.
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  • 54
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    Journal of Chemometrics 6 (1992), S. 65-83 
    ISSN: 0886-9383
    Keywords: Trilinear decomposition ; Receptor modeling ; Source identification ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In many cases, monitoring data for ambient airborne particles can be organized in the form of a three-way data table with one way for chemical species, one for sampling periods and one for sites. A direct trilinear decomposition followed by a matrix reconstruction (DTDMR) is developed to analyze such a data table as a whole. The three-way data set is composed into three two-way matrices by a direct trilinear decomposition (DTD). The column vectors of each of the matrices are called ‘source profiles’, ‘emission patterns’ and ‘site coefficients’ respectively. Particulate sources are identified by examining both their source profiles and emission patterns. After the sources have been identified, emission patterns and site coefficients are used to produce a three-way matrix that gives estimates of mass contributions of sources to the samples collected at every site in every period. By simulation study, not only has the method been verified, but a good indicator has been found that shows the number of factors (i.e. sources) in the system. Unlike other receptor models, DTDMR does not require source profile data and does not involve trial-and-error procedures. Since DTDMR identifies sources based on variations in two dimensions, it has a higher potential to distinguish two sources that have similar chemical compositions. The DTDMR model has provided excellent results with simulated data and has been applied in a real world three-way data set.
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  • 55
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    Journal of High Resolution Chromatography 15 (1992), S. 669-676 
    ISSN: 0935-6304
    Keywords: Selective GC detection of metals ; Atomic emission detection ; Microwave-induced plasma ; Metal-containing compounds ; Metalloporphyrins ; Organomanganese ; Organotitanium ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Element-selective GC detection by microwave-induced plasma atomic emission spectroscopy has been used to examine a wide variety of compounds containing metals, non-metals, and metalloids. “Recipes”, or new selective detection schemes for use with the software of the computer-controlled system, have been developed for the selective detection of boron, aluminum, gallium, titanium, vanadium, chromium, manganese, rhenium, palladium, and platinum. Figures of merit including limits of detection, linear dynamic range, and spectral selectivity over carbon have been established for most of these elements. Gas chromatography - atomic emission detection (GC-AED) has been applied to the selective detection of vanadium, nickel, and iron in metalloporphyrins present in crude oil, manganese-selective detection of methylcyclopentadienylmanganese tricarbonyl (MMT) in gasoline, and titanium-selective detection of reaction mixtures containing titanium catalysts or titanium boride molecular precursors.
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  • 56
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    Journal of High Resolution Chromatography 17 (1994), S. 217-222 
    ISSN: 0935-6304
    Keywords: Size exclusion chromatography ; Gas chromatography - atomic emission detection ; Sample pretreatment ; Metalloporphyrins ; Crude oil ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Size exclusion chromatography (SEC) has been demonstrated to be an effective and reproducible sample pretreatment procedure for removal of heavy oil matrices prior to GC-AED analysis of metalloporphyrins, and for the resolution of volatile metal species into clean and defined fractions. This paper also discusses the results obtained by SEC for determination of the distribution of metallopor-phyrins in crude oils and the correlation between total metal, metal-loporphyrin, and total distillable metal content.
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    Journal of High Resolution Chromatography 17 (1994), S. 223-229 
    ISSN: 0935-6304
    Keywords: Atomic emission detection ; High temperature GC ; GC-AED ; Microwave-induced plasma ; Metalloporphyrins ; Selective detection of metals ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: High temperature gas chromatography-atomic emission spectroscopy is used for the detection of vanadyl, nickel, and iron porphyrins in crude oils. The operational variables are investigated with regard to the effects on performance in high temperature GC-AED. Under optimal conditions, the method provides charactersitic metal distributions for oils from different sources. The method is also advantageous in the study of decomposition of petroleum metal species. Several crude oils were analyzed for the content of the distillable metals in comparison with total metals as determined by a direct spectroscopic method.
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  • 58
    ISSN: 1040-7685
    Keywords: supercritical fluid chromatography ; packed capillary columns ; thermionic detection ; organophosphorus pesticides ; vegetable extracts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Packed capillary supercritical fluid chromatography coupled with thermionic detection was used for the selective determination of nineteen organophosphorus pesticides in vegetable extracts. The chromatographic behavior of some pesticides was studied using seven different stationary phases. Addition of an organic modifier to carbon dioxide was needed to improve peak shape and reduce retention. Quantitation of organophosphorus pesticides in vegetable extracts showed good linearity. Extraction was performed in a one-step extraction procedure using a water-miscible solvent (acetone) and an organic solvent with limited water capacity (dichloromethane). Under these conditions a wide range of both polar and apolar pesticides can be recovered from vegetable extracts down to the 3-25 μg kg-1 level. The recoveries found ranged from 35 to 95% depending on the polarity of the pesticides.
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  • 59
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    Organic Magnetic Resonance 30 (1992), S. 497-499 
    ISSN: 0749-1581
    Keywords: 13C NMR ; o-nitroanisoles ; n-Butyl o-nitrophenyl ethers ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C NMR analyses of substituted o-nitroanisoles and n-butyl o-nitrophenyl ethers are reported.
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  • 60
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    Rapid Communications in Mass Spectrometry 7 (1993), S. 1145-1149 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A method that combines gas chromatography and mass spectrometry (GC/MS) for the determination of N-0923 in human and monkey plasma is detailed. This novel drug holds promise for the treatment of Parkinson's disease. Clinical use of N-0923 will result both in low peak plasma concentrations and in a short half-life; consequently, a highly sensitive method will be required. Previous methods using high-performance liquid chromatography with electrochemical detection have given reliable data in high dose studies in animals to 0.3-1.0 ng/mL in plasma but are not considered adequate for studies at clinical levels in humans. The data in this paper will show that GC/MS can offer a new direction in the determination of N-0923 in human and monkey samples, with reliable data to 25 pg/mL in plasma. This method is presented as a novel approach to the determination of N-0923, and as a starting point for further development.
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  • 61
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The reaction conformations of the metastable molecular ions of the 3-hydroxy steroids were characterized using translational energy (T50%) release values and the ratios of metastable-ion peak heights to those of the main beams determined for the M+· → [M-H2O]+· reactions.
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  • 62
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The normalized unimolecular rate constant for loss of a methyl radical from pent-3-en-2-ol molecular ions with lifetimes ranging from 10-11 to 10-9 s was studied by field ionization kinetics (FIK). The normalized rate curve shows maxima at molecular ion lifetimes of 10-10.5 and 10-10.1 s. Based on results for deuterium and 13C-labelled pent-3-en-2-ol, the maximum at 10-10.5 s is ascribed to loss of the methyl group at the 1-position by a direct cleavage reaction. The maximum at 10-10.1 s is attributed to a 1,2-H shift-initiated rearrangement of the molecular ion, which leads to loss of the methyl group at the 5- and 1-positions. The time dependence of the processes in the form of the maxima on the normalized rate curve is discussed qualitatively in terms of a lower critical energy and a tighter transition state of the 1,2-H shift than those of the direct cleavage reaction. Collision-induced dissociation of the [C4H7O]+ product ions in combination with FIK provides evidence that at molecular ion lifetimes corresponding to the first maximum on the rate curve protonated crotonaldehyde is formed, whereas protonated methyl vinyl ketone and the butyryl cation are formed at times corresponding to the second maximum.
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  • 63
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    Biological Mass Spectrometry 23 (1994), S. 804-805 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 64
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    Journal of Raman Spectroscopy 23 (1992), S. 81-85 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The resonance Raman and far-infrared spectra of n-Bu4NI3 show the coexistence of symmetrical (C2ν) and unsymmetrical (Cs) I3 - species, which are clearly distinguished by varying the wavelength of the excitation line. Only a slight deviation from D∞h symmetry has been deduced for the Br3 - ions in n-Bu4NB3.
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    Journal of Raman Spectroscopy 23 (1992), S. 721-725 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The resonance Raman spectra of (PEDT-DTDSF)2I3 and (PDM-TTF)3I3 organic conductors were measured and analysed to investigate the state of the polyiodide counterions. It was found that both compounds are characterized by the coexistence of I3- and I5- species. The relative concentration of these polyiodides has been shown to be temperature dependent only for the first compound. This was attributed to a thermally induced disordering of the triiodide chains, which leads to a dynamic formation of pentaiodides with increasing temperature.
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  • 66
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    Organic Magnetic Resonance 30 (1992), S. 45-57 
    ISSN: 0749-1581
    Keywords: 13C NMR substituent effects ; Principal component analysis ; Electronegativity correlation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Principal component (PC) or factor analysis was applied to 13C substituent effects (literature SCS values) in α to δ positions of 47 aliphatic frameworks with 4-13 different substituents X. Two PC terms for each substituent X are sufficient to describe 99.3% of all C-α shifts within 〈 ± 0.6 ppm, even in the largest data matrix containing 13 × 47 = 611 shifts; shifts in β. γ and δ positions require a third PC term for a similar percentage SCS accuracy. Scaling problems with the different order of magnitudes between α to δ SCS variations are avoided by analysing the corresponding data sets separately; this approach, together with the large data base, leads to a dominating first PC term for C-α which unambiguously correlates with substituent electronegativities (EN), in contrast to an earlier factor analysis. The same result is obtained by direct comparison of α-SCS with different EN scales, including for the first time group electronegativities. PCs for β to γ SCS indicate only less consistent trends, which again agree partially with results from direct correlations, but not with EN values. The present PC analysis did not include stereochemical descriptors, but furnishes clear distinctions between clusters of (pseudo-) equatorially or axially substituted compounds. The PC loadings for C-α also lead to the unambiguous distinction of primary, secondary, tertiary and quaternary carbon atoms.
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    Organic Magnetic Resonance 32 (1994), S. 93-96 
    ISSN: 0749-1581
    Keywords: 1H NMR ; 13C NMR ; Bile salts ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H and 13C NMR assignments of sodium chenodeoxycholate in aqueous solution were obtained for three different bile salt concentrations. 1H and 13C NMR chemical shifts of sodium chenodeoxycholate and deoxycholate show slight concentration dependence due to micelle formation. Opposite trends in chemical shifts changes for α- and β-protons cause polarization of the steroid nucleus.
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    Journal of Raman Spectroscopy 23 (1992), S. 691-696 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Vibrational spectra of solid tribromofluoromethane at temperatures between 12 K and the melting point were obtained using Raman and infrared techniques, with special emphasis on the lattice modes. No evidence for a solid-state phase transition was found. Lattice peaks are tentatively assigned on the basis of geometrical and intensity arguments. It is shown that the spectra are compatible with a non-centrosymmetric unit cell containing four molecules.
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    Journal of Raman Spectroscopy 23 (1992), S. 451-455 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Raman and infrared spectra of solid bromotrifluoromethane were recorded in both the internal and lattice mode regions at temperatures between 12 K and the melting point. No evidence of a solid-state phase transition was found. Lattice peaks were assigned on the basis of geometrical and intensity arguments, and splittings of internal modes were interpreted in terms of isotopic or crystal field effects. A non-centrosymmetric unit cell containing four molecules was shown to be compatible with the observed spectra.
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    Journal of Raman Spectroscopy 21 (1990), S. 401-405 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effect of static inhomogeneous environmental broadening of resonance Raman excitation profiles was investigated. The roles of diagonal and non-diagonal terms in the two-fold sum over the local mode vibrational states in the excited intermediate electronic state are discussed. The theoretical considerations are illustrated by an analysis of published experimental data for tetradesmethyl-β-carotene in isopentane solution.
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    Organic Magnetic Resonance 28 (1990), S. 275-276 
    ISSN: 0749-1581
    Keywords: 13C NMR ; 1J(CH) ; 2-Nitrocyclohexanones ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR spectra of 22 α-nitrocyclohexanones were recorded and fully assigned. The one-bond C—H coupling constants for the nitromethine resonances of these compounds were also obtained and tabulated.
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  • 72
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyrolysis gas chromatography/mass Spectrometry was applied to the investigation of homopolymers obtained from trimethyl-, n-pentyldimethyl-, n-octyldimethyl- and trideuteromethyldimethyl-vinylsilanes. The electron impact-induced fragmentation of alkanes, alkenes and alkadienes containing two or more corresponding silyl substituents and resulting from pyrolysis of polymers was elucidated. The most characteristic fragmentation patterns of trimethylsilyl-substituted compounds are due to the loss of HSi(CH3)3 and Si(CH3)4 from M+·, the order of which depends on the presence or absence of a double bond in hydrocarbon chain. The same structural parameter determines the probability of the characteristic decomposition of n-alkyldimethylsilyl-substituted compounds through the loss of alkene and alkyl groups from the molecular ions.
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    Rapid Communications in Mass Spectrometry 6 (1992), S. 32-36 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Myoglobins from horse heat muscle, horse skeletal muscle and sperm whale are widely used as calibration standards or test compounds for various mas spectrometric methodologies. In all such cases reproted in the literature, a molecular weight value is used (16950.5 and 17199, respectively) which is based on the assumption that amino acid 122 in this 153 amino-acid-long protein is asparagine, overlooking a published suggestion that it is aspartic acid instead. Since the mass assignment accuracy for matrix-assisted laser desorption mass spectrometry is reproted to be ±0.01% and for electrospray ionization ±0.0025%, and error of one mass unit in ∼ 17000 would be significant. The mass-to-charge ration of ions of the tryptic peptide encompassing amino acid 122 derived from commercially available horse heart and horse skeletal myoglobins, the apomyoglobin of the latter, and the tryptic and chymotryptic peptide of sperm whale myoglobin proved that in both proteins amino acid 122 is indeed aspartic acid, rather than asparagine. This finding was further confirmed by the collision-induced dissociation sectra of the [M+H]+ ions of the tryptic peptides from the horse myoglobins and the chymotriptic peptide from sperm whale myoglobin. Thus, the correct molecular weight of horse myoglobinis 16951.49 and that of the sperm whale protein is 17199.91.
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    Mass Spectrometry Reviews 11 (1992), S. 343-388 
    ISSN: 0277-7037
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    Biological Mass Spectrometry 26 (1991), S. 587-594 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regioselectivity of methyl cation transfer from (CH3)2F+, (CH3)2Cl+ and (CH3)3O+ to 1-phenyl-2-aminopropane was studied by Fourier transform ion cyclotron resonance in combination with collision-induced dissociation and neutralization-reionization mass spectrometry of the stable [M + CH3]+ ions formed in a chemical ionization source. The (CH3)2F+ ion transfers a methyl cation to the NH2 group and the phenyl ring with almost equal probability. Predominant CH3+ transfer to the NH2 group is observed for the (CH3)2Cl+ ion whereas the (CH3)3O+ ion reacts almost exclusively at the amino group. The preference for methylation at NH2 is discussed in terms of a lower methyl cation affinity of the phenyl ring than of the amino group and the existence of an energy barrier for methylation of the phenyl moiety.
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  • 76
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fragmentation of the acetyl- and propionyl-ferrocenes under electron impact together with the rupture of C—CO bonds, characteristic of ketones, also includes elimination of water and migration of the OH group to the central metal atom, which is due to keto-enol tautomerization of the acyl group in molecular or fragment ions.
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    Biological Mass Spectrometry 28 (1993), S. 1562-1569 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion-molecule reactions of the metal-containing ions LM+ (L = (acac)2, acac, C6H6, C5H5; M = In, Ga, Co, Fe, Ni, Cr, Mn, Pd, Rh, Tl, La, Pr, Yb, Nd) with crown ethers in the gas phase were studied. Two major reactions were observed: adduct formation and substitution of a metal atom ligand by a crown ether. The relative abundances of the two reactions depends on the ease with which the metal atom may be reduced. Ligand substitution can involve hydrogen rearrangements with loss of acetylacetone or cyclopentadiene for crown ethers having mobile H atom(s). The use of ion-molecule reactions in the structural characterization of crown ethers and transition metalcontaining ions is discussed.
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    Biological Mass Spectrometry 29 (1994), S. 594-600 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The results of this study have shown that the C2H5I+CH3 ion containing classical and non-classical forms of the ethyl group can be generated by gas-phase ion - molecule reactions. The classical ions fragment by CH4 and CH3⋅ losses, the latter without loss of positional identity of H atoms in the ethyl group. Hydrogen scrambling, however, precedes ethene loss, taking place in an ion of non-classical form. The latter is produced directly from ion - molecule reactions and from energy-rich classical ions. The relative energies of the classical and non-classical ions could not be determined, although the former was proposed to be the global minimum. Finally, the classical ion serves as a source for the ylid ion CH3ICH2+., which previously had eluded preparation.
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    Biological Mass Spectrometry 28 (1993), S. 49-55 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tandem mass spectrometric techniques were used for the characterization of gas-phase titanocenium ions. Decomposition of metastable and collisionally activated C10H10Ti+· ions involved cyclopentadienyl-metal bond rupture, acetylene loss and dehydrogenation as the prominent processes. The intermediate formation of titanium (di)hydride complexes was proposed to explain the selective H2 molecule loss. The neutralization-reionization mass spectrum showed a very abundant recovery signal, indicating a high stability for the neutral gas-phase C10H10Ti species.
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    Mass Spectrometry Reviews 13 (1994), S. 133-154 
    ISSN: 0277-7037
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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    Biological Mass Spectrometry 27 (1992), S. 567-570 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calculations on the thermochemistry of reactions between NH4+ ions and EtHgX molecules (X = Cl, Br, I) were performed by the MNDO method. The calculations showed the possible existence of two stable isomers of composition [EtHgX, NH4]+ namely [EtHgX…HNH3]+ and [EtHg(NH3)XH]+. Protonation of EtHgX and of CH2=CHHgX by NH4+ is characterized by high exothermicity.
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    Biological Mass Spectrometry 26 (1991), S. 746-747 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion-molecule reactions of (acac)2M+ ions (M = Fe, Co) with macrocyclic thiourea derivatives (L) were studied. The formation of acacML+ and acacM(L - H)+ were observed. AcacM(L - H)+ ions arise from loss of the hydrogen atom of the NH group. The ion peak intensity ratios, Z = [acacML+]/[acacM(L - H)+], for M = Co are higher than those for M = Fe, in accordance with the easier reduction of Co(III) to Co(II) than that of Fe(III) to Fe(II). It is proposed that the metal-containing ions preferentially attack the thiourea fragment of the macro-cycles studied.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electron impact mass spectra of substituted norbornadienecyclopentadienylrhodium complexes have been studied. The decompositions of molecular ions are (i) metal-ligand bond rupture, (ii) norbornadiene skeleton destruction, (iii) substituent or hydrogen atom elimination from the norbornadiene moiety and (iv) radical or neutral molecule elimination from the substituent(s) on the diene ligand. Norbornadiene ligand loss occurs more easily than loss of the cyclopentadienyl ring. Elimination of C2H2R and C2H3 from the diene ligand leads to the formation of rhodocenium or its corresponding substituted derivatives. It is proposed that bridging C—C bond rupture followed by migration of the endo-H atom around the six-membered ring precedes the loss of the substituent. Some decomposition pathways of the norbornadiene ligand are explained in terms of specific interaction between the metal atom and substituent.
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    Rapid Communications in Mass Spectrometry 7 (1993), S. 1118-1120 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The female sex pheromone of the China corn borer, Ostrinia furnacalis (Lepidoptera: Pyralidae), was confirmed as Δ12-tetradecenyl acetate by a ‘fuzzy’ similarity analysis of gas chromatograph/mass Spectrometry data.
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    Rapid Communications in Mass Spectrometry 7 (1993), S. 591-593 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A new procedure is presented for locating double-bund position in dodecenols. Ten isomers of chemically unmodified dodecenol were analysed by two kinds of mass spectrometers. A series of spectra obtained with a magnetic sector instrument were interpreted by analysing the similarity of mass spectral patterns based on a ‘fuzzy’ reasoning method, in which the intensity ratios of six diagnostic pairs of the predominant ions were defined as standard parameters. The method was tested with other series of spectra from a quadrupole mass spectrometer, and the original double-bond position in each isomer was located unambiguously.
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    Biological Mass Spectrometry 28 (1993), S. 873-877 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electron impact-induced fragmentations of isomeric dodecen-1-ols were investigated using mass-analysed ion kinetic energy (MIKE) spectrometry and high-resolution data. The principal fragmentation pathways of the positional isomers studied are dominated by the C=C double bond and involve migration and radical-site rearrangements along the carbon chain with the aid of consecutive rearrangements of hydrogen atoms.
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology , Physics
    Notes: Picosecond-excited surface-enhanced hyper-Raman scattering (SEHRS) spectra have been obtained for several non-centrosymmetric oxa- and thia-carbocyanine molecules adsorbed on pre-aggregated colloidal silver. To facilitate interpretation of the SEHRS results, a comprehensive vibrational study of these dyes by employing Fourier transform (FT) IR spectroscopy, surface-enhanced Raman scattering (SERS) and the newly developed techniques of near-IR-excited FT-Raman and FT—SERS is also reported. The SERS spectra of these carbocyanine dyes are dramatically different from their bulk FT-Raman and SERS spectra, but exhibit similarities to their FT—IR spectra. Many SEHRS lines appear to arise from vibrational modes of the central π-conjugated chain, in contrast to the appearance of predominantly end-chromophore vibrations in the Raman spectra. Some of the intense surface hyper-Raman lines are found to be experimentally undetected or unresolvable by Raman scattering and IR absorption. The results thus conclusively demonstrate that, for non-centrosymmetric molecules, surface-enhanced hyper-Raman scattering is capable of providing important vibrational information that is unobtainable through the Raman and IR methods.
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    Biological Mass Spectrometry 25 (1990), S. 645-648 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The positive-ion fast atom bombardment (FAB) mass spectra of stibonium salts have been studied. The spectra exhibit an abundant intact cation (C+) and fragment ions resulting from the loss of R, R′ or stable neutral species from the cation. The principal fragment ions in the FAB mass spectra of stibonium salts are [R3Sb]+·, [R2Sb]+, [R2SbH2]+, [RSbR′]+, [RSbH]+, [RSb - H]+ and [R2SbR']+·. In most cases, [ M + C] + cluster ions were detected. When the anion was bromine, the adduct ions [M + (R - H)Sb]+, [C + (R-H)]+ and [ C + (R′ - H)]+ were also observed, whereas when the anion was [BPh4]-, interesting cluster ions such as [M + (BR′ - H)]+ and [M + (BR′ - 3H)]+ appeared.
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  • 89
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    Journal of High Resolution Chromatography 17 (1994), S. 705-712 
    ISSN: 0935-6304
    Keywords: High performance liquid Chromatography ; Zirconia-based ion exchange ; Proteins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of non-porous, microspherical zirconia-based stationary phases with surface bound cationic functions have been introduced and evaluated in ion exchange chromatography of proteins and small acidic solutes. Different surface modification procedures were evaluated in the covalent attachment of weak, strong or hybrid anion exchange moieties on the surface of non-porous zirconia micropar-ticles. N,N-Diethylaminoethanol (DEAE) was used as the weak anion exchange ligand while glycidyltrimethylammonium chloride, which was covalently attached to poly(vinyl alcohol) layer (PVAN) on the zirconia surface, constituted the strong anion exchange moiety. Partially quaternarized poly(ethyleneimine) hydroxyethylated (PEI) was used as the hybrid type of anion exchange coating. DEAE-zir-conia microparticles acted as purely cation exchange stationary phases toward basic proteins indicating the predominance of electron donor-electron acceptor interaction (EDA) with surface exposed zirconium sites as well as cation exchange mechanism via electrostatic interaction with unreacted and unshielded hydroxyl groups. PVAN-zirconia stationary phase exhibited anion exchange chromatographic properties toward acidic proteins, but EDA interaction has stayed as an important contributor to solute retention despite the presence of a relatively thick layer of poly(vinyl alcohol) on the surface of the zirconia particles. The modification of zirconia surface with partially quaternarized PEI proved to be the most effective approach to minimize Lewis acidic metallic properties of the support. In fact, PEI-zirconia stationary phase operated as an anion exchanger toward acidic proteins and other small acidic solutes.
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  • 90
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    Journal of High Resolution Chromatography 17 (1994), S. 773-778 
    ISSN: 0935-6304
    Keywords: High performance liquid chromatography ; Amino-zirconia sorbents ; Carbohydrates ; Pulsed amperometric detection ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of non-porous, microspherical zirconia-based stationary phases with surface bound amine functionality have been introduced and evaluated in hydrophilic interaction chromatography (HILIC) of underivatized, neutral carbohydrates and anion exchange chromatography of nucleotides using pulsed amperometric detection and ultraviolet detection, respectively. Three aminopropyl alkoxysilane compounds were used in the surface modification of the non-porous zirconia support, namely 3-aminopropyltrimethoxysilane (monoamine), N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (diamine), and trimethoxysilylpropyldiethylenetriamine (triamine). Due to the relatively low specific surface area of the non-porous zirconia support used in this study (ca. 7.3 m2/g), zirconia with surface coating of the triamine type yielded the best results as far as the separations of chitooligosaccharides and maltooligosaccharides are concerned. Since a non-porous zirconia could be readily modified with amine functionality via Zr—O—Si bonds, it is expected that all the three aminopropyl alkoxysilane compounds would yield satisfactory results with porous zirconia microparticles because of their much higher specific surface areas. Although the non-porous zirconia exhibited some limitations, the present study has demonstrated that microspherical zirconia particles are suitable supports for the production of polar sorbents for HILIC of carbohydrates. Another surface modification, which involved the activation of the zirconia surface with aldehyde groups followed by reductive amination with tetraethylenepentamine, was also evaluated. Although this chemistry would in principle yield sorbents with higher concentration in amine groups, the conversion of the majority of the primary amine groups of the tetraethyle-nepetamine molecules to secondary amine functions in the course of the reductive amination reaction have provided a stationary phase that did not afford satisfactory resolution for carbohydrates. However, this same stationary phase behaved as a weak anion exchanger and allowed the high resolution separation of nucleoside-5′-mono-, -di-, and triphosphates. Overall, the results obtained with zirconia-based hydrophilic sorbents paralleled those obtained on amino-silica bonded phases.
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  • 91
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    Organic Magnetic Resonance 30 (1992), S. 30-34 
    ISSN: 0749-1581
    Keywords: NOESY spectrum ; 2QF-COSY spectrum ; Magainin ; 2D NMR ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H and 13C NMR spectra of magainin 1, a sterilizing agent of the skin, were studied using two-dimensional techniques. All the 1H and 13C NMR resonances were unambiguously determined from a combination of 2D homo- and heteronuclear NMR spectroscopy.
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  • 92
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    Journal of Raman Spectroscopy 21 (1990), S. 251-254 
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The effects of the opiates levorphanol and naloxone on the thermotropic properties of dipalmitoylphospalidylcholine (DPPC) multilamellar dispersions were studied using Raman spectroscopy. The spectra of DPPC dispersions were recorded in the C—H stretching mode region. By examining the intensity ratios I2880/I2850 and I2930/I2880 as a function of temperature, it was found that opiates lowered the pretransition temperature of DPPC by 2°C and decreased the lateral packing of the acyl chains of the phospholipids.
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  • 93
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    Rapid Communications in Mass Spectrometry 7 (1993), S. 352-359 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The diazomethane-derived tetramethyl esters of fumonisins can be introduced readily into mass spectrometers using flow injection analysis or liquid chromatography (LC) via a particle-beam interface to yield chemical ionization and electron-ionization spectra. The esters of fumonisins B1, B2, and B3 were well resolved on a C18 reversed-phase column when eluted with a gradient of water + methanol + acetonitrile in the presence of 0.05% trifluoroacetic acid. Enhancement of analyte transport through the particle-beam interface to afford increased ion abundances was achieved by addition of carriers. Polyfunctional amino acid carriers, such as L-glutamic acid or L-serine, effected at least 100-fold increases in sensitivity. In the LC mode, post-column addition of aqueous L-serine was the most advantageous because background interference was limited to lower masses, and because of higher solubility, and ease of cleaning.
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  • 94
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    Rapid Communications in Mass Spectrometry 5 (1991), S. 226-229 
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The high-energy collision-induced dissociation (CID) mass spectra of C60+, C70+, C602+, C702+ and C603+ are reported. In all cases, fragmentation occurs by loss of an even number of carbon atoms, in agreement with photodissociation studies of C60+ and C70+. No charge-separation reactions are observed for the multiply charged ions. Collision-induced dissociation of C60+ leads to a slight preference for formation of C50+, while dissociation of C70+ and C702+ shows a more pronounced preferenced for formation of C60+ and C602+, respecstively. Under electron-capture Chemical-ionization conditions the fullerenes readily capture an electron to form the molecular anions. Collision-induced dissociation of C60- and C70- leads to elimination of 1, 2 and 4 carbon atoms; the elimination of one carbon is unique among larger carbon cluster ions. Charges inversion of the molecular anions leads to formation of the respective molecular cations and fragementation of these cations by loss of an even number of carbon atoms. Formation of C50+ is slightly preferred in the C60- case, while C60+ is the most abundant ion in the charge inversion mass spectrum of C70-.
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  • 95
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    Organic Magnetic Resonance 30 (1992), S. S46 
    ISSN: 0749-1581
    Keywords: Tannin ; Anomer ; Hydrolysable tannin ; Oligomeric hydrolysable tannin ; Heteronuclear long-range ; COSY ; Oenothein B ; Camelliatannin H ; Coriariin H ; Euphorbin C ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structures of hydrolysable tannins, each existing as an equilibrium mixture due to tautomerization at the sugar core(s) or at the dehydrohexahydroxydiphenoyl group (five- and six-membered hemiacetal forms) in the molecule, were elucidated by NMR, employing 2D NMR techniques (COSY, NOESY, 1H—13C long-range COSY, etc.), on derivatives which avoid the spectral complication due to equilibration.
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  • 96
    ISSN: 0749-1581
    Keywords: 31P NMR ; 13C NMR ; Barium ethyl octyl phosphate-water system ; Phase structures ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 31P nuclear magnetic resonance (NMR) studies of the four phases (I, II, II′ and III) in the barium ethyl octyl phosphate-water system were carried out. The concentration dependence of the 31P chemical shift, half-height width and line shape provided information on the phase structures. For phase I the critical micelle concentration (CMC) is found at 1.2 wt.%, and above this concentration there is a monomer ⇌ micelle equilibrium. Phase II has a monomer ⇌ micelle equilibrium system, similar to phase I. Phase II′ is an aggregate system and is structurally organized. The structure of phase III is more organized than that of phase II′ and depends strongly on concentration. The 3J(POCC) values were also used to establish the restricted state of the PO—CC single bond in the phases.
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  • 97
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The identification of rat faecal metabolites of a new antihistaminic agent, ebastine, 4′-tert-butyl-4-[4-(diphenylmethoxy)piperidino]butyrophenone, is presented. After oral administration of (14C)ebastine (20 mg kg-1) to rats, 84% of the radioactive dose was excreted in the 24 h faeces. Unchanged drug and five metabolites were isolated from the faeces by thin-layer chromatography and solid-phase extraction, and their structures were identified by liquid secondary ion mass spectrometry using the B/E linked scanning technique. The main metabolic pathways were oxidation of a terminal methyl group to give the hydroxymethyl and carboxyl derivatives, and hydroxylation of a phenyl ring in the diphenylmethoxy moiety. In addition to the oxidative mechanism, metabolism of ebastine involved sulphate conjugation. It is noteworthy that M-4, having both phenolic and alcoholic hydroxyl groups, was sulphated selectively in the latter position.
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  • 98
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    Biological Mass Spectrometry 21 (1992), S. 479-485 
    ISSN: 1052-9306
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A set of neutral permethylated trisaccharides identical in the non-reducing (A → B) disaccharide and linkage isomeric in the reducing terminal (B → C) disaccharide has been synthesized. Collision-activated tandem mass spectrometry was used for analysis of the B → C linkage position. The trisaccharides, gal(β1 → 4)glc(β1 → X)glc, where X = 3, 4 and 6, were synthesized and examined using fast atom bombardment collision-induced dissociation tandem mass spectrometry. Results were rationalized using molecular modeling. We have previously reported results for determination of the A → B linkage position with isomeric sets of synthetic trisaccharides containing internal amino sugars. The neutral trisaccharides were synthesized to isolate electronic effects of the amino group. An approach of relating daughter ion to parent ion ratios and collision energy offset was used to generate slopes that predict linkage position in glc β1 → X glc reducing end glycoside form of terminal trisaccharides.
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  • 99
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    Biological Mass Spectrometry 25 (1990), S. 397-403 
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A theory has been developed for the determination of the isomeric composition of an ionic mixture. The probability theory describing the collisionally activated decomposition (CAD) which was developed previously provided a general foundation for the present theory. Quantification was based on the cross-sections for the collisional production of daughter ions as observed in the mass-analysed ion kinetic energy Spectrometry (MIKES). Experimental details for the implementation of the theory have also been developed. The method has been applied to the case of C2H4O+· generated from butane-l,3-diol, which is known to be a mixture of more than one isomeric structure. The results seem to be far superior to those based on previous methods, as evidenced by the excellent internal consistency.
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  • 100
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    Journal of Microcolumn Separations 4 (1992), S. 349-362 
    ISSN: 1040-7685
    Keywords: microcolumn liquid chromatography ; liquid chromatography/mass spectrometry ; temperature programming ; optimization methods ; fatty acids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A temperature-programmed microcolumn liquid chromatography/mass spectrometry (LC/MS) system has been developed as a practical alternative to conventional solvent-programmed LC/MS. Good reproducibility of solute retention was achieved in a specially modified oven that permitted linear temperature programming between 40 and 100°C at rates of 0.1 to 0.5°C min-1. Through theoretical modelling studies performed under isocratic and isothermal conditions, the optimum separation under temperature-programmed conditions was rapidly and accurately predicted. This method enabled the complete resolution of saturated and unsaturated fatty acids in a fish oil dietary supplement with identification from their characteristic fragmentation patterns under electron-impact MS conditions. The mass spectra from the LC/MS system correlated very well with those from a standard reference library to facilitate spectral searching methods.
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