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  • Articles  (547)
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  • Analytical Chemistry and Spectroscopy  (547)
  • 1975-1979  (547)
  • 1
    Electronic Resource
    Electronic Resource
    A new surface roughening method for glass capillary columns. Sodium chloride deposition from suspension (1979)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 2 (1979), S. 447-455 
    Details
    ISSN: 0935-6304
    Keywords: Gas chromatography ; Capillary, glass ; Surface roughening by direct deposition of suspension particles ; NaCl used ; High reproducibility when coated with polar phases ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method is described for roughening the surface of glass capillary columns for subsequent coating with polar stationary phases. A suspension of sodium chloride, obtained by addition of a saturated solution of sodium chloride in methanol to 1,1,1-trichloroethane, is passed through the column at velocities of 1-5 cm/s. During passage of the suspension, particles of sodium chloride deposit spontaneously on the column wall. The amount of sodium chloride deposited on the column wall is a function of the volume of the suspension passed through and of the contact time of the suspension and the column wall. Ultimately the amount of sodium chloride per unit surface area approaches a maximum. Columns covered with this maximum amount of sodium chloride were prepared with high reproducibility and coated with a number of polar stationary phases. Various factors that influence the stability of the suspension and the deposition of sodium chloride are discussed and minimum requirements are given. A theoretical model is proposed for the mechanism of deposition of sodium chloride particles on the glass wall.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240020715
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  • 2
    Electronic Resource
    Electronic Resource
    Quantitative evaluation of thin-layer chromatograms. 2. Experimentally confirmed calculations of multilayer models (1979)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 2 (1979), S. 661-666 
    Details
    ISSN: 0935-6304
    Keywords: Thin-layer chromatography, TLC, HPTLC ; Quantitation ; Theory of, confirmed by experimental results on models ; White background for remission measurements is of advantage ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multilayer models of different materials were prepared and scanned. Experimental measurements are compared with mathematically predicted values. This comparison leads to a further development of multilayer models. The advantage of using a white background on a scanning table for remission measurements was confirmed by calculation and experiment.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240021104
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  • 3
    Electronic Resource
    Electronic Resource
    Quantitative evaluation of thin-layer chromatograms. 1. The calculation of remission and transmission using multilayer models (1979)
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 2 (1979), S. 517-523 
    Details
    ISSN: 0935-6304
    Keywords: Thin-layer chromatography, TLC, HPTLC ; Photometric scanning ; Radiation transfer equation ; Multilayer model (10 layers) ; Remission ; Transmission ; Sample concentration ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Quantitative evaluation of TLC by direct photometric scanning is a promising method, in view of the development of cheap microprocessors: soon instruments for digital scanning will be commercialy available. In this paper we describe a multilayer model which seems to be a good approximation for solving the radiation transfer equation in the case of layer models with a gradient in an inward direction. Changes of remitted and transmitted light, in cases where a band lies in different layers, are presented. Examples shown are: the absorbance profile of a chromatographed band in the direction of scanning is approximated to that of an isosceles triangle; the concentration of the band is uniform, e.g. 0.3 A. U.; the concentration of the band is changing from 0 to 2.0 A. U. These results will serve to set up the correct algorithms for digital scanning and simultaneous determination in TLC.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jhrc.1240020806
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  • 4
    Electronic Resource
    Electronic Resource
    Real-time analysis of breath using an atmospheric pressure ionization mass spectrometer (1979)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 6 (1979), S. 91-97 
    Details
    ISSN: 0306-042X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new technique is reported resulting in the direct, instantaneous analyses of trace compounds in breath. The analyses were performed using a commercial atmospheric pressure chemical ionization mass spectrometer (TAGA TM 2000 APCI mass spectrometer). A known flow of breath sample is introduced into the ionization region of the mass spectrometer. The study includes the measurement and monitoring in real-time, of breath ammonia during a 24 hour and a 48 hour period. The ammonia profiles indicate a personalized daily pattern associated with each subject. This method appears to be of potential value in routine detection and treatment of hyperammonemia patients. Results also show that it is possible to obtain instantaneous analyses of several naturally occurring metabolites and other substances on breath in the ppm to ppt range, suggesting a number of diagnostic research applications.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200060302
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  • 5
    Electronic Resource
    Electronic Resource
    1H and 13C NMR study of α-acetylenic PIII and PIV derivatives. Signs and magnitudes of J(P—C) and J(P—H) (1975)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 7 (1975), S. 392-400 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All J(P—H) and J(P—C) values, including signs, have been obtained in acetylenic and propynylic phosphorus derivatives, R2P(X)—C≡C—H and R2P(X)—C≡C—CH3 (X = oxygen, lone pair and R = C6H5, N(CH3)2, OC2H5, N(C6H5)2, Cl) from 1H and 13C NMR spectra. In PIV derivatives the following signs are obtained: 1J(P—C)+, 2J(P—C)+, 3J(P—C)+, 3J(P—H)+, 4J(P—H)—. Linear relations are observed between 1J(P—C), 2J(P—C) and 3J(P—C) versus 3J(P—H), indicating that these coupling constants are mainly dependent on the Fermi contact term, though the other terms of the Ramsey theory do not seem to be negligible for 1J(P—C) and 2J(P—C).In PIII derivatives these signs are: 1J(P—C)- and +, 2J(P—C)+, 3J(P—C)-, 3J(P—H)-, 4J(P—H)+. Only 3J(P—C) and 3J(P—H) reflect a small contribution of the Fermi contact term while in 1J(P—C) and 2J(P—C) this contribution seems to be negligible relative to the orbital and/or spin dipolar coupling mechanisms.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270070808
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  • 6
    Electronic Resource
    Electronic Resource
    The Chemistry of C6H6O radical cations: A study of rearrangement reactions of halogen substituted ethyl phenyl ethers (1979)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 14 (1979), S. 474-481 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New experimental data on the rearrangement reaction of various phenoxyethyl halides to give [C6H6O]+· are presented and compared with previous studies so that a coherent picture of this process can be developed. By examining the metastable kinetic energy release for low energy decomposing molecular ions of the phenoxyethyl halides, it has been concluded that formation of [C6H6O] occurs by competitive 1,2 and 1,3 hydrogen shifts from the alkyl carbons to oxygen followed by a rate determining C—O bond cleavage. This is substantiated by the absence of a primary hydrogen isotope effect. For more highly activated molecular ions, a new mechanism comes into play as evidenced by the appearance of a small hydrogen isotope effect. It is postulated that this third mechanism involves transfer of the alkyl hydrogen to the ortho position of the ring by a rate determining 1,5 shift, followed by a 1,3 hydrogen shift from the ortho methylene group to oxygen and rapid C—O bond cleavage. This 1,3 hydrogen shift to oxygen appears to be ‘catalysed’ by the halogen atoms yielding phenol ions. No indications have been found for the formation of tautomeric 2,4-cyclohexadienone ions. Furthermore, highly activated molecular ions produce [C6H6O]+· which can undergo metastable decomposition to lose carbon monoxide. Kinetic energy release measurements for the latter reaction show that the majority of these [C6H6O]+·ions have been formed as phenol ions as well. These arguments are supported by energetic measurements and by comparisons with previous ion cyclotron resonance and collisional activation studies.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210140904
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  • 7
    Electronic Resource
    Electronic Resource
    Sélénophènes substitués. Additivité de l'influence des substituants sur les couplages J(H—H) et J(Se—H) (1976)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 8 (1976), S. 508-512 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The spin-spin coupling constants J(H—H) and J(Se—H) of 2- and 3-substituted selenophenes, whose signs have been obtained by double resonance experiments, have been correlated with the reactivity constants F and R of Swain and Lupton by means of linear equations J = i + fF + rR. The relative inductive and mesomeric contributions to the coupling constants are discussed. Substituent effects on J(H—H) and J(Se—H) are found to be additive in 2,4-disubstituted selenophenes. In agreement with experimental results, this additivity relationship indicates that 3J(Se—H) becomes negative in 2,4-dinitroselenophene.Evidence is given from long range coupling constant data that 2-formylselenophene exists almost exclusively in the Se—O cis conformation and 3-formylselenophene in the Se—O trans conformation.
    Notes: Les différents couplages J(H—H) et J(Se—H) mesurés dans divers sélénophènes 2- et 3-substitués, dont les signes ont été déterminés par double résonance, ont été reliés aux constantes de réactivité de Swain et Lupton par des équations linéaires J = i + fF + rR. L'importance relative de la contribution des effets inductifs et mésomères est discutée. Dans les sélénophènes 2,4-disubstitués, l'effet des deux substituants sur les couplages J(H—H) et J(Se—H) est additif. Cette loi d'additivité rend compte du changement de signe de 3J(Se—H) observé dans le dinitro 2,4-sélénophène. Les conformations préférentielles des formyl 2- et 3-sélénophènes, déduites des couplages à longue distance, sont respectivement Se—O cis et Se—O trans.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270081005
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  • 8
    Electronic Resource
    Electronic Resource
    Field ionization mass spectrometry of higher n-alkenes (1978)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 13 (1978), S. 181-183 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a strong electric field the molecular ions of n-alkenes ≤C-12 decompose via cleavage of the C—C bond β to the double bond to form the characteristic alkenyl ions that may be used for the identification of positional isomers. For 3-alkenes (〉C-10), 4-, 5- and 6-alkenes the formation of the ions with m/e 54 via double β-cleavage is typical. The field ionization mass spectra of the cis and trans isomers are indistinguishable.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210130402
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  • 9
    Electronic Resource
    Electronic Resource
    [C]+· and [CH]+ from doubly charged ions formed from malononitrile (1975)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 10 (1975), S. 824-830 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The metastable ions [M]2+, [M - H]2+· and [M - H2]2+ from malononitrile fragment by loss of [CH]+, [C]+· and [C]+·, respectively. The reaction of the molecular ion involves the methylene and nitrile carbon atoms in the statistical probability ratio, while that of [M - H]2+· involves exclusively the nitrile carbon and that of [M — H2]2+ involves an approximately equal contribution, from both sources. It is suggested that the metastable molecular ion fragments through a bipyrimidal intermediate.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210101003
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  • 10
    Electronic Resource
    Electronic Resource
    Pyrolysis mass spectrometry of methionine (1977)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 12 (1977), S. 334-337 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mechanisms of some fragmentation of methionine upon Curie-point pyrolysis have been studied by the use of deuterium labelling. They lead to products having the same nominal mass but essentially different elemental compositions compared with ions generated by electron impact on methionine. For exaple, upon pyrolysis the product with mass 116 is due to a 1,2 elimination of hydroxylamine from the title compound, whereas upon electron impact the ion with m/e 116 is generated by successive loss of a molecule of water and of a methyl radical from the molecular ion; the generated of product m/e 101 proceeds via successive loss of a molecule of water, carbon monoxide and of hydrogen upon pyrolysis, but via a one-step elimination of methanethiol upon electron impact. No evidence has been found for a diketopiperazine formation by a bimolecular process upon pyrolysis, although this type of reaction is well known for α-amino acids.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210120516
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