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  • Column liquid chromatography  (495)
  • 36.40.+d  (210)
  • Springer  (705)
  • American Chemical Society
  • American Chemical Society (ACS)
  • 1990-1994  (705)
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  • Springer  (705)
  • American Chemical Society
  • American Chemical Society (ACS)
  • Wiley-Blackwell  (4)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 58 (1994), S. 57-62 
    ISSN: 1432-0649
    Keywords: 32.80.Pj ; 42.50.Vk ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The mechanism responsible for transitions of laser-cooled trapped ions from an ordered “crystal” state to an irregular “cloud” state has been discussed controversially. A numeric and analytic study of the relative motion of two trapped ions without laser cooling is performed and compared with the results of previous simulations involving the laser. It turns out that the system without laser, in spite of its simplicity, already exhibits a non-monotonic dependence of crystal stability on trap parameters, which is linked to the presence of low-order nonlinear resonances.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 55 (1992), S. 364-371 
    ISSN: 1432-0630
    Keywords: 79.20.N ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The emission of dimers during bombardment of a Cu(001) surface by Cu atoms of 300 and 1000eV energy is studied. A molecular dynamics simulation method based on many-body potentials is employed. At 300eV bombarding energy, around 81% of the sputtered dimers originate from second-nearest neighbor sites. 58% of these are ejected in a collision sequence correlated by the projectile. These dimers lead to a second maximum in the kinetic energy distribution of emitted dimers at around 8eV, besides a maximum at 4eV. Only the latter is found at 1000eV bombarding energy. As in this case mostly next-neighbor surface atoms are sputtered, the specific emission mechanism found at 300eV is irrelevant. Finally, we show that the direction of the angular momentum of sputtered dimers is correlated with the original surface site of the dimers.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 56 (1993), S. 215-217 
    ISSN: 1432-0630
    Keywords: 71.25.Mg ; 71.25.Rk ; 71.20.−b ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A tight-binding method which has been previously applied to study the effect of uncorrelated orientational disorder on conduction-band properties is extended here to the case of systems with long-range order and/or short-range correlations. The density of states and conductivity are not highly sensitive to the specific short-range correlations, so long as the system is not too close to being fully ordered. Hence the strong effects of disorder found previously appear to be robust and should play an important role in the interpretation of normal-state properties of A3C60.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 57 (1993), S. 101-104 
    ISSN: 1432-0630
    Keywords: 73.20.Mf ; 82.65.Pa ; 82.50.−m ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Laser-induced desorption of metal atoms from the surface of small metal particles has been investigated as a function of the shape of the particles and the polarization of the incident laser light. The particles were supported on LiF, quartz or sapphire substrates. In a first set of experiments, the shape of the particles was determined by recording optical transmission spectra with s- and p-polarized light incident under an angle of typically 40° with respect to the surface normal. The metal particles turn out to be oblate, the ratio of the axes perpendicular and parallel to the substrate surface being on the order of 0.5. This ratio decreases with increasing particle size. Also, the particles change shape if the temperature is raised. In further experiments, s- and p-polarized light has been used to stimulate desorption of atoms via surface plasmon excitation. It is found that the desorption rate markedly depends on the polarization of the light. This is explained by excitation of the collective electron oscillation along different axes of the non-spherical particles.
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  • 5
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Bovine milk ; Multivariate optimization ; Glycerophospholipids ; Molecular species separation ; Chemometrics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The molecular species profile, representing the fatty acid combinations on the glycerol backbone, is the most fundamental description of an intact glycerophospholipid class and provides a key to understanding its functional characteristics. We have developed a powerful RP-HPLC method for the separation of molecular species, including so-called “critical pairs”, of natural mixtures of 1,2-diacyl-sn-glycero-3-phosphocholine 1,2-diacyl-sn-glycero-3-phosphoethanolamine from bovine milk and other natural sources. We have used a novel multivariate development and optimization strategy to locate the region of optimum separation conditions within a prechosen domain of the chromatographic parameter space.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Open tubular columns ; Cross-linked polyacrylate stationary phase ; Photopolymerization ; Antracene derivatives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Polyacrylate films containing a lauryl moiety were fabricated on about 12 μm I.D. fused silica capillaries by in-situ photopolymerization of acrylates. Relatively thick films up to 1 μm were obtained by the technique. The films were tested as retentive layers for reversed phase open tubular liquid chromatography (OTLC). Due to the presence of the incorporated lauryl moiety in the layer considerable retention could be achieved for polar compounds with aqueous mobile phases. The efficiency of the prepared columns approximates to the theoretical value. The polyacrylate films appear to be extremely stable even under strong basic conditions. The films swell considerably in the presence of nonpolar solvents resulting in more favourable retention and a significant improvement of the chromatographic performance.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 627-630 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fatty acid analysis ; Fish oils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A chromatographic method has been developed for the determination of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in fish oil dietary supplements containing triglycerides rich in (n−3) polyunsaturated fatty acids (PUFAs). Following the ester saponification, free fatty acids were resolved by TLC into two fractions: i) a more mobile group of saturated and monounsaturated fatty acids and ii) a less mobile group containing PUFAs. The PUFA fraction was further analyzed by HPLC to determine the levels of EPA and DHA in the fish oil sample.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Carbidopa and levodopa in plasma ; Electrochemical detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A validated reversed-phase high-performance liquid chromatographic procedure employing electrochemical detection (LCEC) for the analysis of carbidopa and levodopa in human plasma is reported. The method is sensitive and specific with amperometric detection at a glassy carbon working electrode with Eapp=0.75 V vs. Ag/AgCl. The retention times of levodopa, internal standard, and carbidopa are 3.3, 4.5, and 9.7 minutes, respectively, with an overall chromatographic run time of 12.0 minutes. The peak height ratio versus plasma concentration is linear over the range of 5.0 to 500 ng/mL for each analyte and exhibits correlation coefficients of 0.9957 or better (n=9). The mean absolute recovery of carbidopa and levodopa using the described assay is 36.6 and 66.0%, respectively. The inter- and intra-day accuracy and precision are within 11.8% of the actual values for all concentrations. Also, due to the demonstrated instability of carbidopa and levodopa in plasma a procedure is provided to circumvent this. Blood collected in pre-treated Vacutainer tubes can be stored in an ice bath for up to 4 hours without any significant degradation, thereby providing a practical means for processing several clinical samples simultaneously.
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  • 9
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Fullerenes ; FullereneSep® ; Separation factor ; HPLC-particle beam mass spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High-performance liquid chromatographic separation of fullerene mixtures in the range C60 to C100 can be achieved using a novel stationary phase which rivals the performance of the more expensive ‘Pirkle-type’ columns currently employed.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Chromatographia 35 (1993), S. 675-678 
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Trace metal determination ; Sample contamination ; Human hair
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The dynamic ion-exchange chromatographic analysis of bivalent ions, such as Cu, Pb, Zn, Ni, Co and Mn in resistant organic matrices needs preliminary wet ashing with oxidizing acids (HNO3 and HClO4). Such treatment may lead to an increase in the amounts of metals present in the sample due to their release from containers or equipment used in an acidic environment and to metal impurities contained in the acids. The effect of these interferences in the determination of trace metals in human hair was studied.
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