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  • 1
    Electronic Resource
    Electronic Resource
    Enhanced Resolution of Conjugated Linoleic Acid Isomers by Tandem-Column Silver-Ion High Performance Liquid Chromatography (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 144-148 
    Details
    ISSN: 0935-6304
    Keywords: Conjugated linoleic acid (CLA) ; silver-ion high performance liquid chromatography (Ag+-HPLC) ; cheese ; analysis ; silver-ion chromatography ; tandem-column Ag+-HPLC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A commercial mixture of conjugated linoleic acid (CLA) isomers, reportedly consisting of six components, was recently resolved into 12 peaks attributed to CLA isomers using silver-ion high performance liquid chromatography (Ag+-HPLC). In this study, the coupling of two analytical silver-ion high performance liquid chromatography columns (tandem-column Ag+-HPLC) in series led to the enhanced resolution of CLA isomers. Many CLA isomers were baseline resolved and the pair 18 : 2 8,10 c/t and 18 : 2 7,9 c/t found in cheese products, was resolved for the first time. In this work, a similar commercial CLA mixture was separated into 16 peaks, while CLA isomers from cheese also gave rise to 16 peaks. As expected, the CLA isomers were separated into three geometric groups in the order trans,trans, cis/trans, and cis,cis. Semi-preparative Ag+-HPLC, followed by gas chromatography-mass spectroscopy of the dimethyloxazoline derivatives, was used to confirm the identity of the newly resolved positional CLA isomers. The double bond configuration of CLA isomers was established by gas chromatography-Fourier transform infrared spectroscopy. Two minor t,t CLA isomers found in cheese, presumably 18 : 2 t6t8 and 18 : 2 t13t15, were also separated. The CLA isomeric composition of 16 commercial cheese products was determined.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    A Robust Thermal Modulator for Comprehensive Two-Dimensional Gas Chromatography (1999)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 22 (1999), S. 3-10 
    Details
    ISSN: 0935-6304
    Keywords: Multidimensional Gas Chromatography ; orthogonal separations ; GC×GC ; comprehensive two-dimensional chromatography ; characterization of gasoline ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In comprehensive two-dimensional gas chromatography (GC×GC), two capillary columns are connected in series through an interface known as a “thermal modulator”. This device transforms effluent from the first capillary column into a series of sharp injection-like chemical pulses suitable for high-speed chromatography on the second column. Dramatic increases in the resolving power, sensitivity, and speed of the gas chromatograph result. This paper describes the development of a robust and reliable thermal modulator for GC×GC.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Assignment of the 1H NMR resonances of D-glycero-D-ido- and D-glycero-D-altro-octulose mono- and bisphosphates (1995)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 33 (1995), S. 231-232 
    Details
    ISSN: 0749-1581
    Keywords: NMR ; 1H NMR ; D-glycerol-D-ido-octulose phosphates ; D-glycero-D-altro-octulose phosphates ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H NMR chemical shifts of the various contributing forms of the mono- and bisphosphates of D-glycero-D-ido- and D-glycero-D-altro-octuloses were determined by two-dimensional NMR spectroscopy.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1260330314
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  • 4
    Electronic Resource
    Electronic Resource
    A second-order standard addition method with application to calibration of a kinetics-spectroscopic sensor for quantitation of trichloroethylene (1995)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 263-282 
    Details
    ISSN: 0886-9383
    Keywords: multiway data ; standard addition method ; calibration ; matrix effects ; trilinear decomposition ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Presented here is an algorithm for analysis of second order data by the method of standard additions. The method of standard additions is applicable when matrix effects make traditional calibration unreliable. The algorithm employs a generalized eigenproblem to mathematically separate the instrument response of the analyte from the instrument response of any interfering species. A scheme for determining the eigenvectors (and hence the concentration estimate) that uniquely correspond to the analyte of interest is given. These eigenvectors can readily be distinguished from any eigenvector that corresponds to the spectrum of the interferents or both the interferents and analyte. The stability of the estimated analyte concentration is verified by Monte Carlo simulations. The algorithm is applied to the analysis of trichloroethylene in samples that have matrix effects caused by an interaction with chloroform.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180090403
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  • 5
    Electronic Resource
    Electronic Resource
    Simulated-annealing-based optimization algorithms: Fundamentals and wavelength selection applications (1995)
    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 283-308 
    Details
    ISSN: 0886-9383
    Keywords: simulated annealing ; threshold acceptance ; wavelength selection ; selectivity ; optimization ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simulated annealing (SA) is a stochastic search method that has been applied to combinatorial search problems in chemometrics. Unlike strict iterative improvement methods, SA tolerates temporary moves to detrimental parameter configurations during an optimization. The method used by SA to decide whether or not to accept detrimental steps is a special case of a more general acceptance rule. The present work investigates the performance of various SA-type algorithms that differ only in the acceptance rule for detrimental steps when optimizing continuous or discrete problems. A method for step width modulation is introduced to overcome the poor ability of SA type algorithms to locate the exact extreme of a function. The studied search strategies are modified for the discrete problem of wavelength selection. In order to evaluate SA-type algorithms and their abilities to deal with the wavelength selection problem, two global measures of selectivity are used as criteria to determine the most suitable wavelength subset that maximizes selectivity for pure component ultraviolet-visible spectra.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cem.1180090404
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of underivatized tetrapeptides by negative-ion fast-atom bombardment mass spectrometry (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 677-685 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The [M — H]- ions derived from tetrapeptides generally show two different collision-induced backbone cleavages which allow the determination of the amino acid sequence of the peptide. The first of these involves the formation of the carboxylate anions of either constituent amino acids or fragment peptides. In the second, amino acids or fragment peptides are eliminated as neutrals. There are a number of residues which undergo characteristic sidechain fragmentations irrespective of their position in the tetrapeptide, e.g. Ser, Thr, Cys, Met, Phe and Tyr. However, there are also some residues which, when situated at the C-terminal end of the peptide, promote pronounced fragmentation at the C-terminal position which occurs to the exclusion of the normal backbone cleavages. We conclude that the data obtained from these negative-ion cleavages are analytically useful, and complement those provided by the cognate positive-ion technique.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290090810
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  • 7
    Electronic Resource
    Electronic Resource
    Investigation of ‘ghost’ peaks caused by non-linear fields in the ion trap mass spectrometer (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 107-113 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Mass spectral ‘ghost peaks’ are generated with the ion trap by the superposition of higher order multipole fields which originate through deviations from the pure quadrupole field. In data acquisition, when the amplitude of the RF voltage is ramping though a non-linear resonance point (q*) on the Mathieu stability diagram, some ions (m0) are ejected by the non-linear field rather than by the quadrupole field at qz=0.908 on the βz=1 boundary. The prematurely ejected ions will be seen as a peak at m1=(q*/0.908)m0, which we have termed a ‘ghost peak’.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290090202
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  • 8
    Electronic Resource
    Electronic Resource
    Award announcements (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 1473-1473 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290091429
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  • 9
    Electronic Resource
    Electronic Resource
    Conformational properties of Rhodobacter capsulatus cytochrome c2 wild-type and site-directed mutants using hydrogen/deuterium exchange monitored by electrospray ionization mass spectrometryPublication no. 292 of the Institut de Biologie Structurale. (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 1135-1140 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The conformational properties of Rhodobacter capsulatus cytochrome c2 wild-type and two site-directed mutants (glycine 34 replaced by serine and proline 35 replaced by alanine) were characterized by their charge state distributions and hydrogen/deuterium (H/D) exchange properties monitored by electrospray ionization mass spectrometry. The results suggest the presence of structural perturbations in the mutated cytochromes, an observation that is in agreement with their decreased conformational stabilities. In addition, a fast enzymatic procedure was developed to identify regions for which the H-bonding or solvent accessibility properties were perturbed by the mutations. In this procedure, deuterated peptides were separated and analysed by using liquid chromatography directly coupled to the electrospray ionization source in order to minimize the occurrence of back-exchange during analysis. In the case of G34S, mutational effects were found for peptides 1-26, 38-51, 52-59 and 109-116, which in the Rb. capsulatus cytochrome c2 structure correspond to extensive regions on the same side of the molecule as the proximal histidine, as well as part of the C-terminal helix. In the case of P35A, mutational effects were found for peptides 1-26, 27-37, 38-51 and 52-59, which in the Rb. capsulatus cytochrome c2 stucture correspond to extensive regions on the same side of the molecule as the proximal histidine. We show that the present set of mass spectrometric experiments is useful as an initial characterization of mutant conformational properties because the analyses require only nanomole quantities of protein and can be performed rapidly.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290091211
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  • 10
    Electronic Resource
    Electronic Resource
    Unusual cross-ring SN2 reactions of [M—H]- ions of methoxyacetanilides (1995)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 9 (1995), S. 177-179 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: Deprotonated o, m-, and p-methoxyacetanilide show pronounced peaks in their collision-induced tandem mass spectra (MS/MS) produced by losses of the elements of C2H6. It is proposed that this reaction is a ‘cross-ring’ internal SN2 reaction involving an incipient methyl anion. For example, p-CH3O—C6H4—-—CO—CH3→ [(p-CH3O—C6H4—N=C=O)CH3-]→-O—C6H4—N=C=O+C2H6.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290090214
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