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  • Column liquid chromatography  (88)
  • 36.40. +d  (35)
  • Springer  (123)
  • 1990-1994  (123)
  • 1970-1974
  • 1950-1954
  • 1991  (123)
Collection
Keywords
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  • 1990-1994  (123)
  • 1970-1974
  • 1950-1954
Year
  • 1
    Electronic Resource
    Electronic Resource
    Retention characteristics of chlorinated polycyclic aromatic hydrocarbons in normal phase HPLC. I. Chloro-added PAHs (1991)
    Springer
    Chromatographia 32 (1991), S. 334-340 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Normal phase separations ; Cyanopropyldimethyl silica ; Chloro-added polycyclic aromatic hydrocarbons ; Environmental samples
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention characteristics in normal phase HPLC of highly biologically active chloro-added polycyclic aromatic hydrocarbons (PAHs) were studied. Silica, cyanopropyldimethylsilyl- and aminopropylsilyl- modified stationary phases were investigated. Retention properties of chloroadded PAHs on these phases were shown to be strongly influenced by the number of chloro-additions. This is due to the strong polarity of the methylene carbon at the chloro-addition site. Active silica had a strongly degrading effect on the unstable chloro-added PAHs during separation. Aminopropylsilica did not exhibit sufficient selectivity towards chloro-added PAHs when compared to chlorosubstituted PAHs. Cyanopropyldimethylsilica was shown to be applicable to a group separation of chloro-added and chloro-substituted PAHs. A fast clean-up procedure for chloro-added PAHs in complex samplesis outlined. It involves an initial elimination of more polar substances on a short open column with strongly deactivated silica and a subsequent separation on a cyanopropyldimethylsilyl HPLC column in normal phase mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02321430
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  • 2
    Electronic Resource
    Electronic Resource
    Chromatography in pore networks II — The role of structure and adsorption in the band broadening (1991)
    Springer
    Chromatographia 32 (1991), S. 345-349 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Column packings ; Pore size distribution ; Diffusion and adsorption ; Band broadening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The complex intraparticle structure typical of chromatographic column packings has been analyzed by use of an equivalent network model which emphasizes pore size distribution and connectivity. Special attention is given as to the way in which diffusion and adsorption interact and display modified peak spreading characteristics according to the morphology of the pore space. This study reveals a very significant increase in the column band broadening over that expected from physical adsorption which can arise from particular distributions of pore sizes. This has implications for designing packings which take advantage of the separating power due to adsorption but do not compromise the resolution of the chromatographic system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02321432
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic shells and shells of atoms in metallic clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 25-29 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 82.80Ms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Intensity anomalies (magic numbers) have been observed in the mass spectra of sodium clusters containing up to 22 000 atoms. For small clusters (Na n ,n≤1500) the anomalies appear to be due to the filling of electronic shells (groups of subshells having the same energy). The shells can be characterized rather well by a pseudoquantum-number, indicating the possible existence of a symmetry higher than spherical. The mass spectra of larger clusters (1500≤n≤22 000) are well explained by the completion of icosahedral or cuboctahedral shells of atoms. The fact that the two types of shells (electron and atom) occur in distinct and non-overlapping size intervals might indicate the existence of a “liquid” to “solid” transition in going from small to large clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448248
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  • 4
    Electronic Resource
    Electronic Resource
    Electronic structure of selenium- and tellurium-clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 233-235 
    Details
    ISSN: 1434-6079
    Keywords: 33.60.Cv ; 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The vacuum-UV-photoelectron spectra (hν=10.0 eV or 8.3 eV) of selenium- and tellurium-clusters of different sizes (up to Se25 and Te8) were measured in a molecular beam by a photoion-photoelectron-coincidence experiment. Especially, the photoelectron spectra (4p-π-electrons) of the selenium-clusters converge with growing cluster size to the well known spectra of amorphous solid selenium by taking into account the dielectric constant of the bulk material. The experimental results indicate the first evidence that larger selenium aggregates are van der Waals clusters of the molecules Se5, Se6, Se7 and Se8 which are contained in the equilibrium vapour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448300
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  • 5
    Electronic Resource
    Electronic Resource
    Comparison between selenium and tellurium clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 237-239 
    Details
    ISSN: 1434-6079
    Keywords: 35.20.Vf ; 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Selenium and tellurium clusters are produced by the inert gas condensation technique. The mass spectra of both species are completely different and reveal different properties. In selenium, a periodicity of 6–7 is observed and may be interpreted by the binding energy between small cyclic molecules. Moreover, it was very difficult to obtained large clusters probably because the binding energy between these molecules is very small. In tellurium, these periodic structures do not exist and large clusters are easily obtained in nucleation conditions where only small selenium clusters are present. These results are discussed and a simple nucleation model is used to illustrate this different behavior. Finally these clusters properties are correlated to the bulk structure of both materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448301
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic properties of free alkali and transition metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 241-245 
    Details
    ISSN: 1434-6079
    Keywords: 75.50.Bb ; 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Stern-Gerlach deflections of small alkali clusters (N〈6) and iron clusters (10〈N〈500) show that the paramagnetic alkali clusters always have a non-deflecting component, while the iron clusters always deflect in the high field direction. Both of these effects appear to be related to spin relaxation however in the case of alkali clusters it is shown that they are in fact caused by avoided level crossing in the Zeeman diagram. For alkali clusters the relatively weak couplings cause reduced magnetic moments where levels cross. For iron clusters however the total spin is strongly coupled to the molecular framework. Consequently this coupling is responsible for avoided level crossings which ultimately cause the total energy of the cluster to decrease with increasing magnetic field so that the iron clusters will deflect in one direction when introduced in an inhomogeneous magnetic field. Experiment and theory are discussed for both cases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448302
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  • 7
    Electronic Resource
    Electronic Resource
    Metallic susceptibility in giant molecule: Pd561Phen36O200 (1991)
    Springer
    The European physical journal 19 (1991), S. 267-270 
    Details
    ISSN: 1434-6079
    Keywords: 75.20.−g ; 35.20.My ; 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The giant metal cluster molecule Pd561Phen36O x is the largest member of a series that has recently been prepared by Schmid [1]. Pronounced size effects are expected to show up in the magnetic properties of metal particles of the size of the Pd-561 core of the molecule. We have measured the susceptibility on four different batches of the material, with quite satisfactory reproducibility. There is a low temperature tail that is attributed to small amounts of impurities. The nearly temperature-independent paramagnetism that is observed is most probably due to an exchange enhanced Pauli spin susceptibility and is already close to the bulk value. The absence of size effects, i.e. a drop at low temperatures, is either due to interactions between the clusters or a result of a very small energy level spacing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448308
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  • 8
    Electronic Resource
    Electronic Resource
    Electronic properties of divalent-metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 165-167 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The transition from van der Waals to metallic bonding expected to occur in divalent-metal clusters (e.g., Be n , Mg n , Hg n ) as a function of cluster size is discussed. Theoretical results for several electronic properties reflecting this transition in Hg n -clusters are briefly reviewed and compared with available experiments. The limitations of the present theory particularly concerning the role of correlations and van der Waals interactions are discussed and possible improvements are suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448282
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  • 9
    Electronic Resource
    Electronic Resource
    Semiclassical variational calculation of liquid-drop model coefficients for metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 101-103 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 31.20.Lr ; 31.20.Sy ; 03.65.Sq
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report on semiclassical density variational calculations for spherical alkali metal clusters in the jellium model. We derive liquid-drop model expansions for total energy, ionisation potential and electron affinity and test the coefficients numerically for clusters with up toN=105 atoms. From the limitN→∞, we obtain excellent agreement with surface tensions and work functions evaluated for an infinite plane metal surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448265
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  • 10
    Electronic Resource
    Electronic Resource
    Ultraviolet photoelectron studies of the molecules Se5, Se6, Se7 and Se8 with relevance to their geometrical structure (1991)
    Springer
    The European physical journal 19 (1991), S. 229-231 
    Details
    ISSN: 1434-6079
    Keywords: 31.20. +Z ; 33.60.Cv ; 35.20.Vf ; 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The vacuum-UV-photoelectron spectra (hν=10.0 eV) of Se2, Se5, Se6, Se7 and Se8 were measured. The isolated particles were examined in a supersonic molecular beam employing the photoelectron-photocation-coincidence technique. The structures of the photoelectron spectra of selenium molecules with even and odd numbers of atoms differ in a characteristic manner. Whereas the spectra of Se6 and Se8 show one single broad band, three separated bands with different intensities are observed for Se5 and two for Se7. An attempt to connect these experimental observations with the geometrical structure of the molecules shows that the photoelectron spectra are consistent with theC 1h -symmetry of the Se5 and Se7 rings proposed in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448299
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  • 11
    Electronic Resource
    Electronic Resource
    Simple metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 1-6 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 35.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The response of alkali cluster ions to an optical excitation is investigated for two different photon energy domains. Below the ionization potential giant resonances in the photoabsorption cross-section are observed for closed shell species. Above the ionization potential, the ionization process competes with the photofragmentation process. The number of valence electrons determines both the behavior of the photoabsorption spectrum and the evolution of the ionization cross-section with the cluster size. The stability of the clusters against an excess of charge is examined through the observation of an asymmetric fission of Na n ++ . Experimental results are discussed in term of an electrostatic model giving an estimate of the critical size of stability and of the height of the coulombic barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448244
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  • 12
    Electronic Resource
    Electronic Resource
    Optical spectra of sodium microclusters (1991)
    Springer
    The European physical journal 19 (1991), S. 43-45 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 33.20.Kf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photoabsorption spectra have been measured for free neutral sodium clusters containing fromN=3 to 40 atoms. In the size range ofN≈3 to 5, a transition occurs from molecule-like absorption to collective excitations of the valence electrons. ForN≈6 to 12, the data are well described by an ellipsoidal shell model. In open-shell clusters, the multiple surface plasma resonances expected for spheroidal or ellipsoidal shapes are observed. The experimental resonance positions provide a sensitive measurement of the cluster distortions. ForN≳13, the per atom strength of these collective resonances is reduced; this may be due to peak fragmentation caused by interaction between the surface plasmon and nearby single-electron resonances. In three distinct wavelength regions, one of which corresponds to the position of the Na atom “D-lines”, additional absorption is seen in the spectra of all investigated clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448251
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  • 13
    Electronic Resource
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    Thermal electronic properties of alkali clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 51-53 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 31.20.Sy ; 05.30.−d ; 65.60. +m
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We apply the finite-temperature Kohn-Sham method to alkali metal clusters, using the spherical jellium model and treating the valence electrons as a canonical system in the heat bath of the ions. We study the shell effects in the total free energyF(N) and the entropyS(N) for neutral clusters containingN atoms. Their strongest temperature dependence is due to the finite ground-state valueS 0〉0 of the electronic entropy for non-magic clusters. It leads to a decreasing amplitude and an increasing smear-out of the saw-tooth structure in the first difference Δ1 F(N)=F(N−1)−F(N) with increasing temperatureT and cluster sizeN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448253
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  • 14
    Electronic Resource
    Electronic Resource
    Applying ZEKE-spectroscopy to clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 59-61 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 33.60. −q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we describe the application of a special form of electron photodetachment spectroscopy, zero electron kinetic energy (ZEKE) spectroscopy, to the study of cold metal cluster anions. From this study we have obtained vibrational and thus structural information of several neutral and charged clusters, e.g. Au 2 −/0 , Ag 3 −/0 , Sn 2 −/0 and Al 3 −/0 . In addition, in separate measurements of the relative photodetachment cross section of Au 2 − , we have discovered sharp resonances which are due to electronic autodetachment from a short lived excited state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448255
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  • 15
    Electronic Resource
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    A pseudo-Jahn-Teller treatment of the B system of Na3 (1991)
    Springer
    The European physical journal 19 (1991), S. 63-66 
    Details
    ISSN: 1434-6079
    Keywords: 33.10 Lb ; 33.70. −w ; 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract TheB system of the two-photon ionization spectrum of Na3 often is quoted as an example of fractional quantization of the pseudorotational motion. In the present paper we investigate the influence of a nearby electronic state on the nuclear motion. It turns out that the experimental results may be understood equally well in a picture which implies integer instead of fractional quantization of the pseudorotation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448256
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  • 16
    Electronic Resource
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    Photoabsorption spectra of Cs n O and Cs n clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 81-84 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 33.20 Ea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photoabsorption spectra of several Cs N+2O and Cs N clusters were obtained by means of laser-induced beam-depletion techniques. The strong absorption of clusters withN≥3 in the near infrared indicates that collective motion might play an important role. Dipole transitions between molecular orbitals, enhanced by plasmon oscillations, generate remarkably distinct spectra for(a) closed-shell clusters atN=8 and(b) geometrically symmetric clusters like Cs6O and Cs14O.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448260
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  • 17
    Electronic Resource
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    The response of metal clusters toq- andL-dependent external fields (1991)
    Springer
    The European physical journal 19 (1991), S. 89-91 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 31.20.Sy ; 71.45.Gm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have calculated the static polarizability and mean excitation energy of metal clusters submitted toq-andL-dependent external fields ofj L (qr)Y L0(Ω) type. Use has been made of an Extended Random-Phase Approximation which includes exchange and correlation effects within a local model, and of the spherical jellium model to describe the neutralizing positive background.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448262
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  • 18
    Electronic Resource
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    Surface and volume collective modes in small clusters and their interaction with single-particle levels (1991)
    Springer
    The European physical journal 19 (1991), S. 105-107 
    Details
    ISSN: 1434-6079
    Keywords: 36.40. +d ; 72.45. −d ; 31.20.Lr
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract As has been recently established, collective excitations in small metal clusters exhibit some unusual features. A theoretical analysis of cluster photoabsorption spectra is presented. It is shown that small systems can support volume collective modes which, unlike in the case of bulk metals, make a noticeable contribution to photoabsorption. Furthermore, single particle-hole transitions cause splitting of resonance peaks. The theory agrees well with experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448266
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  • 19
    Electronic Resource
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    The self-consistent spheroidal jellium model of open-shell monovalent metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 109-111 
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    ISSN: 1434-6079
    Keywords: 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recently, we have proposed a microscopic model, describing the properties of open-shell, Jahn-Teller deformed monovalent-metal clusters [1]. The model is based on the self-consistent ground-state calculation, allowing the spheroidal (axial) deformation of the ionic jellium background, driven by the open-shell valence electron structure. The ground state electronic properties of such clusters are further investigated and compared to recent experimental data: ionization potentials, electron affinities and binding energies of neutral monomers to cationic clusters [2].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448267
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  • 20
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    Calculated electronic properties of medium sized sodium clusters: the inhomogeneous jellium model (1991)
    Springer
    The European physical journal 19 (1991), S. 113-115 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 31.20.Sy ; 71.25.M
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recently observed magic number data for Na N clusters in the size range from 100 to 900 atoms cannot be fully explained by density functional calculations using a homogeneous, spherical positive charge background. However, a centrally compressed spherical background yields steps in the ionization potential at just those magic numbers observed experimentally.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448268
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  • 21
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    Investigation of large electronic shells in Cs-compound clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 117-119 
    Details
    ISSN: 1434-6079
    Keywords: 71.50. +t ; 31.20.Sy ; 36.40. +d ; 82.80.Ms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Magic numbers in cluster mass spectra can be caused by either geometric or electronic structure. The study of metallic compound clusters allows the number of atoms and the number of electrons in clusters to be controlled independently. We report magic numbers in the mass spectra of Cs-compound clusters containing up to 700 free electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448269
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  • 22
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    Multipotential model for atoms in alkali microclusters (1991)
    Springer
    The European physical journal 19 (1991), S. 121-124 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 21.60.Cs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An alkali-atom shell model for alkali microclusters is introduced, where the quantum constituent is the neutral atom itself considered as a heavy fermion in a central potential created by all atoms in each shell of the cluster. Thus, here the magic numbers are due to atoms and not to electrons as in jellium models. The model is applicable under conditions (of production, temperature, size, etc.) not favoring delocalization of valence electrons. For conditions favoring electron delocalization the jellium model is applicable. New experiments are suggested via nuclear methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448270
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  • 23
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    Small clusters made up of three kinds of neutral alkali atoms (1991)
    Springer
    The European physical journal 19 (1991), S. 125-127 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 21.80. +a
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Small clusters made up of three kinds of neutral alkali atoms, i.e. clusters of the form X ℓ Y m Z n , are theoretically studied. These clusters exhibit three series of magic numbers, one for each kind of atoms. That is,ℓ,m, andn independently can be magic numbers rather than their cumulative numberℓ+m+n or, in other words, magic numbers in alkali clusters composed of neutral atoms are due to atoms rather than to delocalized electrons as in jellium model. Of course, if conditions favor delocalization of electrons,ℓ+m+n can be magic but then we have no neutral atoms which are prerequisite for an application of the present model.
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    URL: http://dx.doi.org/10.1007/BF01448271
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  • 24
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    Electronic properties of aluminum clusters compared with the jellium model (1991)
    Springer
    The European physical journal 19 (1991), S. 133-135 
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    ISSN: 1434-6079
    Keywords: 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The experimental polarizabilities, ionization potentials and electron affinities of aluminum clusters are compared with jellium predictions. It is found that the clusters have radii and work functions which are close to the jellium model predictions for clusters with more than 13 atoms. The polarizabilities of Al n correspond with the jellium only forn〉40 and the shell structure features in the ionization potentials are anomalous up to 37. We conclude that nonjellium effects are important up ton=40.
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    URL: http://dx.doi.org/10.1007/BF01448273
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  • 25
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    Stability of isomeric Na n clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 141-143 
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    ISSN: 1434-6079
    Keywords: 31.20.Sy ; 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A method which combines density functional theory and the use of pseudopotentials is applied to obtain ground state and low-lying metastable geometries of Na n clusters (7≤n≤40). The large variation in the magnitude of energy gaps between isomers suggests that the melting temperature is not a simple monotonous function of size. A detailed study of the differences between electronically stabilized (n=8, 20, 40) and structurally stabilized (n=13) clusters suggests some clues to understand the intriguing behaviour of Na13.
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    URL: http://dx.doi.org/10.1007/BF01448275
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  • 26
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    Shell effects on fragmentations of doubly-charged silver clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 149-150 
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    ISSN: 1434-6079
    Keywords: 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Shell effects are found in the size distributions of fission fragments from doubly-charged silver clusters. The energy differences between parent cluster and sum of a pair of fragmented clusters are calculated for various fission channels using the theory of shell corrections. Oscillative structures observed in the size distribution are shown to be due to shell effects of fragments. It is also found that the cluster deformation due to shell effects produces the even-odd alternation in the size distribution.
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    URL: http://dx.doi.org/10.1007/BF01448277
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  • 27
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    Shell effects on symmetric fragmentations of alkali-metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 145-147 
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    ISSN: 1434-6079
    Keywords: 36.40. +d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Symmetric fragmentation of multiply charged alkali-metal clusters consisting of several tens of atoms is studied. The energy variation during the fragmentation process is calculated using the theory ofshell corrections, in which total energy is written as a sum of the liquid-droplet and shell correction terms. It is found that the variation of the shell correction term is much larger than that of the liquid-droplet one if the parent cluster is metastable. Fragmentation into nearly-magic cluster is most favored regardless of parent size since the barrier height for fragmentation is mainly determined by the shell configuration of fragments rather than that of the parent.
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    Electronic shell structure in multiply charged silver clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 151-152 
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    ISSN: 1434-6079
    Keywords: 36.40. +d
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    Topics: Physics
    Notes: Abstract Silver clusters are generated by standard laser vaporization technique and ionized via multiphoton ionization. Time-of-flight mass spectrometry reveals singly, doubly and triply charged clusters, Ag n z+ (z=1,2,3). The spectra show, for all charge states, intensity variations, indicating enhanced stabilities for cluster sizes with closed electronic configurations in accord with the spherical jellium model.
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    Photoelectron spectroscopy and UV/Vis-photoabsorption spectroscopy of isolated clusters (1991)
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    The European physical journal 19 (1991), S. 161-164 
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    ISSN: 1434-6079
    Keywords: 33.60.Cv ; 35.20.Vf ; 36.40. +d
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    Topics: Physics
    Notes: Abstract Experimental innovations have allowed for the application of rather conventional spectroscopic molecular beam techniques to the study of electronic properties of molecular beam isolated neutral aggregates. Recent results for mercury clusters obtained by photoelectron spectroscopy and photoabsorption spectroscopy will be discussed. The experimentally available data for mercury clusters indicate a size dependent gradual evolution of metallic bulk properties in the approximate size region between 13 and 70 atoms.
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    Optical spectroscopy on size selected gold clusters deposited in rare gas matrices (1991)
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    The European physical journal 19 (1991), S. 157-159 
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    ISSN: 1434-6079
    Keywords: 29.25.Cy ; 36.40. +d ; 78.40. −q
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    Topics: Physics
    Notes: Abstract We report on the successful “soft-landing” of size selected Au trimers in solid Krypton matrices. The Au cations are produced by sputtering, mass-selected in a quadrupole mass spectrometer, co-deposited with Krypton on a cooled CaF2 substrate, and neutralized by low energy electrons. The deposition of low kinetic energy cations (10 eV) gives rise to strong excitation bands, detected by the emitted fluorescence light, which are unambiguously attributed to Au trimers. The deposition and fragmentation process is qualitatively discussed.
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    Bonding properties of IIA and IIB dimers in density functional theory with gradient corrections to the local density approximation (1991)
    Springer
    The European physical journal 19 (1991), S. 169-171 
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    ISSN: 1434-6079
    Keywords: 31.20. −d ; 31.20.Sy ; 36.40. +d
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    Topics: Physics
    Notes: Abstract We have computed bonding properties of the IIA and IIB homonuclear dimers within the Pseudopotential — Density Functional scheme, including Gradient Corrections to the Local Density Approximation (LDA). Our computations confirm that Gradient Corrections offer a significant improvement over LDA for what concerns ground state properties of finite systems: The LDA error on bond energies is reduced by more than 50%. Although less impressive, the relative improvement on equilibrium distances and vibrational frequencies is also systematic and important. We briefly discuss the relevance of our results to the description of the non-metal to metal transition expected in clusters of these elements as a function of size.
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    Structural and dynamical properties of magnesium microclusters (1991)
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    The European physical journal 19 (1991), S. 173-176 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 31.20.Sy ; 61.50.Cj
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    Topics: Physics
    Notes: Abstract We present systematic Density Functional Theory-Local Density Approximation computations for neutral Magnesium clusters Mg n withn≤13. For the smaller sizes the ground state structure is optimized starting from selected symmetries and allowing for relaxation, Jahn-Teller distorsion and spin polarization. For the larger sizes we perform a simulated annealing based on the ab-initio Molecular Dynamics. By the same method, we study the thermal and dynamical properties of Mg10 and Mg16. The general picture emerging from these computations shows that already atn ≈10 these clusters have acquired many characteristic features of metallic Magnesium.
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    Structure of small rare earth clusters (1991)
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    The European physical journal 19 (1991), S. 191-193 
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    ISSN: 1434-6079
    Keywords: 35.20.Vf ; 36.40. +d
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    Topics: Physics
    Notes: Abstract Rare earth clusters are produced by the inert gas condensation technique. The observed size distribution shows large peaks atn=13, 19, 23, 26, 29, 32, 34, 37, 39, 45, ... The beginning of this sequence (up to 34) has been already observed in argon clusters and recently by our group in barium clusters; this sequence may be interpreted in terms of icosahedral structures corresponding to the addition of caps on a core icosahedron of 13 atoms.
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    Generation of rare earth metal clusters by means of the gas-aggregation technique (1991)
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    The European physical journal 19 (1991), S. 195-197 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 35.20 Wg
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    Topics: Physics
    Notes: Abstract Generation of rare-earth clusters is achieved using a gas aggregation technique. Varying the nucleation conditions induces a change in the relative cluster abundances. This can be understood in terms of competing cubic versus icosahedron structures.
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    Photoabsorption spectra ofs 1-electron metal clusters (1991)
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    The European physical journal 19 (1991), S. 13-17 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 33.80.Gj ; 33.20Kf
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    Topics: Physics
    Notes: Abstract Collinear laser/molecular beam photodepletion spectroscopy has developed into a powerful tool for the determination of electronic absorption in neutral alkali metal clusters free of perturbing matrix effects. We briefly discuss the method, present data on selected Na x and Li y Na x−y ,x≤20, contrast measurements with the known optical response of larger colloidal metal clusters, compare microcluster spectra with the predictions of various models and speculate on future experimental and theoretical developments in this field.
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    Silver-halogen cluster compounds Ag n X m (n≥2; 0≤m≤n;X=F, Br) (1991)
    Springer
    The European physical journal 19 (1991), S. 401-404 
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    ISSN: 1434-6079
    Keywords: 36.40. +d
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    Topics: Physics
    Notes: Abstract Nonstoichiometric silver-halogen cluster compounds Ag n X m (0≤m≤n;X=F, Br) are generated by cocondensation of Ag atoms and AgX species using a slightly modified gas aggregation technique. The AgX molecules are produced by partial decomposition of SF6 and Br2 respectively at the surface of the hot silver containing crucible, followed by the reaction of halogen atoms with silver, giving rise to the formation of AgX molecules. In a heterogeneous nucleation between these molecules and evaporated Ag atoms the afore mentioned cluster compounds are formed. The degree of halogenation can either be controlled by the adjustment of the silver evaporation rate, or even more easily by controlling the partial pressure of the halogenating agent. The mass spectra of singly charged halogenated clusters, which are generated by electron impact ionization, reflect the stability of ions. These mass spectra demonstrate that there is an alternation in the intensity pattern up to a relatively high degree of halogenation (m) for each of the investigated compound series Ag n X m ,n≤8. This behavior is similar to the well-known odd-even effect for pure metal clusters, allowing us to postulate the existence of a “metallic” core which governs the stability of the cluster ion (at least for not too high degree of halogenation).
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    Size effect in3He n aggregates. A Gutzwiller approach (1991)
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    The European physical journal 20 (1991), S. 273-276 
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    ISSN: 1434-6079
    Keywords: 36.40. +d ; 31.20.Tz ; 67.50. -b
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    Topics: Physics
    Notes: Abstract The Hubbard hamiltonian (where only intraatomic correlations between fermions are taken into account) is particularly well suited for the description of3He systems. It has already been used in the description of point defects (such as spin polarons) in the bulk. The variational Gutzwiller method is one of the most useful way for treating the Hubbard hamiltonian. This technique has been applied with success by Vollhardt to the bulk. We apply it here to aggregates. Our main results are the following: 1 existence of a critical size,N c , above which3He n begin to be stable; 2 calculation of the magnetic susceptibility. In this part two cases are studied: low magnetic field where only the density of states, σ(E F), at the Fermi level is needed and high magnetic field where the whole density of states is needed. The results are compared with other theoretical calculations.
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    Separation and characterization of a viscosity index improver copolymer by high-performance liquid chromatography (1991)
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    Chromatographia 31 (1991), S. 71-74 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Size exclusion chromatography ; Styrene-methacrylate polymers ; IR and UV spectroscopy ; Lubricating oils additives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Characterization of a poly(styrene-alkyl methacrylate) viscosity index improver according to its chemical composition distribution and molecular weight distribution was carried out by liquid adsorption chromatography, size exclusion chromatography and infrared and ultraviolet spectrophotometry. The industrial polymer was fractionated by liquid chromatography using silica gel as adsorbent and a mixture of 1,2-dichloroethane and methanol as mobile phase. Each fraction was analyzed by size exclusion chromatography and infrared and ultraviolet spectroscopy. The number average molecular weight ranged from 10000 to 36000 and the weight average molecular weight from 19000 to 264000. The styrene content of the various fractions analysed was between 29.5% and 72.2%.
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    Determination of laidlomycin and 26-deoxylaidlomycin by high-performance liquid chromatography (1991)
    Springer
    Chromatographia 31 (1991), S. 603-605 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Laidlomycin, 26-deoxylaidlomycin
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    Topics: Chemistry and Pharmacology
    Notes: Summary High performance liquid chromatography on an octadecyl silica column has been used to determine laidlomycin: 26-deoxylaidlomycin ratios and to determine the concentration of both compounds by standard addition in samples prepared from fermentation broths ofStreptoverticillium olivoreticuli. A refractive index detector was preferred to an ultraviolet detector owing to the presence of UV-absorbing impurities which could not be completely separated from the substances of interest. Linear relationships were obtained from the calibration data. The coefficient of variation for the estimation of ratio and concentration of the compounds determined was better then 5%. The estimated limit of detection for both substances was about 50μg·ml−1.
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    Prediction of retention of O-ethyl, O-aryl and N-isopropyl phosphoroamidothioates in RP-HPLC from molecular structure parameters (1991)
    Springer
    Chromatographia 31 (1991), S. 143-146 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Molecular structure parameters ; Prediction of retention ; Phosphoroamidothiotes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Multi-variable regression analysis between lnkw, c (in retention equation lnk′=lnkw+cCb) and molecular structure parameters, including hydrophobicity, electric effect, field effect and position-specific effect constant, was carried out with O-ethyl, O-aryl and N-isopropyl phosphoroamidothioates as test solutes. With these quantitative relationships, the retention behaviour of these solutes for different mobile phase compositions was predicted. The results showed that there are only 26.7% of total, experimentally measured, capacity factors with relative deviations larger than 5% and only 2.2% with deviations larger than 10%, which means that it is possible to apply the method reported to predict retention values for qualitative purposes for different mobile phase compositions.
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    A method for the determination of histamine in wine by HPLC with precolumn derivatization with phenylisothiocyanate (1991)
    Springer
    Chromatographia 31 (1991), S. 133-136 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Histamine in wine ; Pre-column derivatization ; Solid phase extraction
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    Topics: Chemistry and Pharmacology
    Notes: Summary A method for determining histamine in wine by precolumn derivatization with PITC (phenylisothiocyanate) with reversed-phase HPLC and UV detection is reported. Histamine can be determined together with the 24 amino acids within 40 min, or separately in a shorter time (less than 4 min) if a prior solid phase extraction clean-up is used.
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    Retention behavior of the inclusion complexes of some polycyclic aromatic hydrocarbons with β-cyclodextrin (1991)
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    Chromatographia 31 (1991), S. 157-162 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cyclodextrin inclusion complexes ; Structure-retention relationships ; Polycyclic aromatics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention behaviour of a group of polycyclic aromatic hydrocarbons having nearly equal ionization potentials but different molecular polarizability values was investigated by reversed-phase HPLC and gas chromatography, using β-cyclodextrin as a selective inclusion reagent. In HPLC, the cyclodextrin was applied as an additive to the ethanolwater binary mobile phase, while in gas chromatography β-cyclodextrin served as the stationary phase coated on an inert support. The relationships between the capacity factors, molecular polarizabilities and the shape parameter of solute molecules is discussed.
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    Quantitation of cortico-steroids as common adulterants in local drugs by HPLC (1991)
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    Chromatographia 31 (1991), S. 67-70 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Cortico-steroids ; Drug adulterants
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    Topics: Chemistry and Pharmacology
    Notes: Summary A sensitive and specific method for quantitation of the steroids betamethasone, prednisolone and cortisone acetate commonly used as adulterants in locally produced herb extracts and in certain homeopathic drugs is described. Reverse-phase liquid chromatography with UV detection has been used.
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    Chromatography of inorganic anions on poly(vinyl alcohol) gel columns with acidic eluents (1991)
    Springer
    Chromatographia 31 (1991), S. 80-84 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion chromatography ; Poly(vinyl alcohol) gel ; Inorganic anions ; UV detection for IC
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Poly(vinyl alcohol) (PVA) gel shows ionic retention properties for common inorganic anions when an acidic eluent is used. The ionic property of the PVA gel is due to the proton-acceptable nitrogen atoms of the cross-linking agent and the carboxylic residues being comprised in the gel matrix. The extent of the net charge on the gel surface depends on the pH of the eluent. At a pH ranging from 2.3 to 5.3, the PVA gel behaves as a weak anion exchanger with very low ion-exchange capacity. At these conditions four UV-absorbing inorganic anions (bromate, bromide, nitrate, and nitrite) are separated by eluting with aqueous sulfuric acid. Alkyl groups introduced on the gel surface hinder the ionized solute molecules from accessing to the positively charged functional groups on the gel surface. A neutral solute (HNO2) is retained with non-ionic interactions.
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    Influence of injection conditions in reversed-phase high-performance liquid chromatography of chlorophylls and carotenoids (1991)
    Springer
    Chromatographia 31 (1991), S. 589-594 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Injection conditions ; Chlorophylls and carotenoids ; Extraction solvents ; Phytoplankton pigments
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The RP-HPLC analysis of chlorophylls, their degradation products (chloropigments) and carotenoids is very sensitive to the nature of the injection solvent. The effect of sample-solvent interaction can result in the production of distorted, or even false, peaks that could be erroneously interpreted as “pigment like” or as poor chromatographic resolution. The previously suggested theoretical explantion, based on differences in solvent characteristics as expressed by the Polarity Index (P′) or even by the more precise solvent strength parameter for reversed-phase systems (S) we use, was unsatisfactory. The problem seems more complex, with other parameters such as injection volume and solute concentration or solvent selectivity also playing a role. As a practical consequence, however, suggesions are made for optimum injection conditions. Also, the presence of ion-pairing reagents in the injection solvent is demonstrated to be unnecessary.
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    The influence of end-capping on the enantioselectivity of a chiral phase (1991)
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    Chromatographia 31 (1991), S. 129-132 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; End-capping ; Chiral stationary phase ; Enantioselectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effect of end-capping chiral stationary phases (CSP's) derived fromN-(2-naphthyl)alanine undecyl ester has been examined using either trimethylchlorosilane (TMCS), hexamethyldisilazane (HMDS), or bis(trimethylsilyl) trifluoroacetamide (BSTFA) as end-capping reagents. The separation factor (α) and capacity factor (k′) of the enantiomers ofN-(3,5-dinitrobenzoyl)leucine octadecyl amide andN-(3,5-dinitrobenzoyl)alanine butyl ester were evaluated on three columns all packed with material from the same batch of stationary phase. These columns were essentially identical before, but not after end-capping with the above reagents. TMCS and HMDS were found to be superior to BSTFA, which appears to cause a significant loss of bonded phase from the silica surface. It seems that residual silanols affect the retention either by interacting with the analyte or by interacting with strands of stationary phase. End-capping usually increases enantioselectivity, sometimes by decreasing k′ for the first enantiomer and increasing k′ for the second enantiomer. The enhancement in enantioselectivity is greatest in relatively nonpolar mobile phases and occurs to a greater extent for phases having incomplete surface coverages.
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    Chromatographic characterization of a bonded liquid crystal stationary phase for HPLC (1991)
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    Chromatographia 31 (1991), S. 147-151 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Liquid crystal bonded phase ; Polycyclic aromatics ; Carvone and pulegone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A chromatographic and thermodynamic study of the compound [4-(allyloxy)benzoyl]-4-methoxyphenyl (ABMP) as a model of a chemically bonded liquid crystal stationary phase for HPLC was undertaken. A number of polycyclic aromatic hydrocarbons (PAHs) and two small solutes, carvone and pulegone, were studied under varying solvent and temperature conditions. Plots of log k′ vs. % organic in the mobile phase were not completely linear in all cases. The van't Hoff plots revealed at least one phase transition. The enthalpies of solute transfer from the mobile phase to the ABMP phase were determined for several PAHs. All tests indicate that ABMP possess liquid crystal properties when bonded to particulate silica.
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    Silica surface controversies, strong adsorption sites, their blockage and removal. Part II (1991)
    Springer
    Chromatographia 31 (1991), S. 193-205 
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    ISSN: 1612-1112
    Keywords: Gas chromatography ; Column liquid chromatography ; Silanol adsorption centres ; Strongly interacting adsorption sites ; Suppression of adsorption activity
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    Topics: Chemistry and Pharmacology
    Notes: Summary In this second part of the review heterogeneity of the silica surface is described and evidence is presented for the existence of a low population of strong adsorption sites. Methods of detection and determination of these strongly interacting sites are discussed. The last part of the review is devoted to the suppression of unwanted adsorption activity. Methods of blockage and special methods for the preparation of HPLC packings are described.
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    A rapid HPLC determination of narasin in fermentation broth (1991)
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    Chromatographia 31 (1991), S. 277-280 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Simplex optimization ; Narasin in fermentation broth ; Vanillin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid HPLC assay with post-column derivatization has been developed for the determination of narasin in fermentation broth. The reaction of narasin with substituted benzaldehydes was investigated under first order conditions and the rate constants were determined for a variety of substituted benzaldehydes. Vanillin reacted most rapidly to produce a red color. The reaction conditions were optimized to acheive a maximum response with a minimum analysis time.
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    The effects of pH and alcoholic organic modifiers on the direct separation of some acidic, basic and neutral compounds on a commercially available ovomucoid column (1991)
    Springer
    Chromatographia 31 (1991), S. 329-334 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ovomucoid stationary phase ; Chiral separations ; Mobile phase effects ; Protein conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The effects of alcoholic modifiers and pH on the chromatographic properties of an immobilized ovomucoid chiral stationary phase have been investigated using acidic, basic and neutral solutes. A series of primary, secondary and tertiary alcohols and pH's ranging from 3.5 to 6.0 were used in this study. The results indicate that both the shape and the hydrophobicity of the alcoholic modifier affect retention (k') and enantioselectivity (α). In general, an increase in the hydrophobicity of the modifier results in a decrease in k's and α's. However, this is not the case whent-butanol is the modifier, suggesting that the size of the alkyl moiety attached to the carbinol carbon also contributes to the chromatographic results. The pH studies indicated that Coulombic interactions play a role in the retention of the acidic and basic solutes. The results also suggest that in addition to ethanol and 1-propanol,t-butanol should be considered during optimization and that maximum efficiencies may be obtained at pH 5.0.
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    Influence of the mobile phase composition on the adsorption isotherms of an amino-acid derivative on immobilized bovine serum albumin (1991)
    Springer
    Chromatographia 31 (1991), S. 323-328 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Adsorption isotherms ; Immobilized serum albumen ; Chiral stationary phase ; Leucine, N-benzoyl derivative
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The saturation capacity of columns packed with bovine serum albumin immobilized on silica has been determined for the N-benzoyl derivative of leucine at different compositions of a 1-propanol/water mobile phase. In all cases it has been found that the equilibrium adsorption data are well accounted for by a biLangmuir isotherm. The experimental data are consistent with the assumption that the column saturation capacity of the chiral selective sites as well as the saturation capacity of the non-selective sites are independent of the 1-propanol concentration in the range 0–10%.
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    New synthesis of alkyldihydrosilanes and their applications in modification of silica gel (1991)
    Springer
    Chromatographia 31 (1991), S. 335-341 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Bonded phase synthesis ; Alkyl and aryldimethyl phases ; CP/MAS NMR spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A comparison of newly synthesized, reversed-phase bonded stationary phases is presented. The materials studied include monomeric n-octyl, n-octadecyl, aryl and n-octyldihydrogeno bonded-phases. Differences in reactivity of the silane functional groups are demonstrated and the high coverage obtained with the hydrogeno-bonded phases is shown. The structures of the bonded phases have been determined by29Si and13C CP/MAS NMR spectroscopy.
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    Comparison of surface states of chemically modified silicas in aqueous acetonitrile and methanol (1991)
    Springer
    Chromatographia 31 (1991), S. 347-350 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chemically modified silicas ; Surface states ; n-alkylbenzenes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The thermodynamic behaviour of n-alkylbenzenes on chemically modified silicas in reversed-phase liquid chromatography has been examined in acetonitrile-water and methanol-water systems. Plots of the thermodynamic parameters obtained against the organic solvent compositions indicate an interesting trend which implies that the surface states of the chemically modified silicas under the two eluent systems are different.
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    A particle size distribution analysis of stressed HPLC column packing material (1991)
    Springer
    Chromatographia 31 (1991), S. 362-366 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Particle size distribution ; Stationary phase stress ; Silica gel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A particle size distribution analysis has been completed on three different HPLC column packing materials including silica gel (Si60) and two bonded phases (RP8 and RP18). The stationary phases were subjected to 18 hours stress with 1 N or 3 N KOH and found to have quantitatively different distribution patterns initially, at 13 hours and finally at 18 hours although the average particle diameters for the Si60 and RP8 were the same or higher at 18 hours as initially. Thirteen hoursstress with sodium octanesulfonate, tetrabutylammonium phosphate and ammonium acetate at exaggerated conditions also resulted in distributional changes with the Si60 and RP8 decreasing in average particle diameter when exposed to ammonium acetate and tetrabutylammonium stressing respectively.
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    URL: http://dx.doi.org/10.1007/BF02262193
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    Separation of food-related biogenic amines by ion-interaction reversed-phase high performance liquid chromatography. Tyramine, histamine, 2-phenylethylamine, tryptamine and precursor aminoacids. Application to red wine (1991)
    Springer
    Chromatographia 31 (1991), S. 381-386 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Biogenic amines ; Wine ; Food-related biogenic amines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Methods for the separation of food-related biogenic amines (histamine, tyramine, 2-phenylethylamine and tryptamine) have been developed based on ion-interaction reversed-phase liquid chromatography. Two different interaction reagents have been comparatively used, namely octylamine ortho-phosphate (at wave-lengths of 230, 254 and 280 nm) and octylamine salicylate (at a wavelength of 254 nm). The different elution sequence orders shown by the investigated amines for the two reagents are discussed and compared. The detection limits obtained were 20 ppb for tryptamine (λ =280 nm), 500 ppb for 2-phenylethylamine (λ=254 nm), 400 ppb for tyramine (λ=230 or 280 nm) and 900 ppb for histamine (λ=230 nm). The method was applied to the analysis of a five years old Italian red wine, in which 2-phenylethylamine (at a concentration of 72±3 ppm) and tryptamine (at a concentration of 4.0±0.3 ppm) were found to be present.
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    Estimation of the degree of self-association of water using a novel retention model (1991)
    Springer
    Chromatographia 31 (1991), S. 387-392 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Retention model ; Self-association of water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An attempt has been made to gain a semi-quantitative insight into the self-association of water molecules through hydrogen bonds. This was only possible with the use of a new solute retention model for the chromatographic systems by considering intermolecular interactions between the constituents of binary mobile phases. Four different sizes of the average associative aqueous multimer were assumed. By comparing measured and calculated retention values, the existence of associated aqueous multimers consisting of 100 aqueous monomer units is postulated as an average multimer structure.
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    Analysis of nucleotides, nucleosides, nucleobases in cells by ion-pair reversed-phase HPLC (1991)
    Springer
    Chromatographia 31 (1991), S. 401-410 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair reversed-phase separations ; Nucleotides ; Extraction from cells and tissue ; Retention mechanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary HPLC methods for the separation of nucleotides, nucleosides and nucleobases by ion-pair reversed-phase are reviewed. The advantages of these are discussed versus anion-exchange and reversed phase separations. Extraction procedures for nucleotide determinations from cells and tissues are pointed out in detail. Extracts from red blood cells, Ehrlich ascites tumour cells, hepatocytes, intestine are used for determination of nucleotide concentrations by the methods described.
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    Automated HPLC-amino acid determination of protein hydrolysates by precolumn derivatization with OPA and FMOC and comparison with classical ion exchange chromatography (1991)
    Springer
    Chromatographia 31 (1991), S. 441-447 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion exchange chromatography ; Quantitative amino acid analysis ; OPA/FMOC precolumn derivatization ; Cheese
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An improved HPLC method for the quantitative determination of the amino acids from hydrolysed cheese proteins and peptides is described. Some important improvements to the existing method are suggested. The addition of piperidine-4-carboxylic acid (PICA) as a hydrolysis-resistant internal standard enabled the quantification of secondary amino acids. The following analytical parameters have been determined: repeatability, detection limit and linearity in the measuring range. A statistical comparison with the classical ion chromatographic method gave an excellent correlation for all determined amino acids. Both methods are free of artifacts and systematic errors. Compared with ion chromatography, HPLC shows the following advantages: faster equilibration of the column, shorter retention times, more stable baseline, narrower peaks and more sensitive fluorescence detection. A drawback is the slightly lower repeatability for some amino acids.
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    Chiral amino acid microanalysis by direct optical resolution of fluorescent derivatives on BSA-based (resolvosil) columns (1991)
    Springer
    Chromatographia 31 (1991), S. 429-433 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral separations ; Amino acids ; Fluorogenic derivatization ; N-(Chloroformyl)-carbazole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A new reagent for fluorescence labelling of amino acids, N-(chloroformyl)-carbazole, has been used in order to achieve high sensitivity of detection as well as good optical resolution. The derivatization reaction is fast and conveniently carried out at room temperature by shaking a buffered aqueous solution of the amino acids with an acetone solution of the reagent. The individual derivatized amino acids are first separated and collected via chromatography on a standard octadecyl-silica column. Each amino acid derivative is then analyzed for enantiomer composition by re-injection on a BSA-silica (Resolvosil®) column using fluorescence detection. For some amino acids (alanine, threonine, phenylalanine, tryptophan) enantiomeric separation factors exceeding α=3 have been obtained. The phosphonic acid analogue of alanine (1-aminoethylphosphonic acid) was also found to be well resolved into its enantiomers.
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    Analysis of catechins and proanthocyanidins in grape seeds by HPLC with photodiode array detection (1991)
    Springer
    Chromatographia 31 (1991), S. 465-468 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Catechins ; Grape seeds ; Proanthocyanidins ; UV-visible spectroscopy/diode array detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Reversed-phase, high-performance liquid chromatography coupled to photodiode array detection has been used to analyse catechins and proanthocyanidins extracted from grape seeds. Results show that the ethyl acetate fraction obtained by passing extracts of samples adjusted to pH 7.0 through preconditioned C18 SEP-PAK cartridges contains several catechins and proanthocyanidins. Seven peaks have been assigned to standard catechins and proanthocyanidins on the basis of their retention times and UV spectra. Other peaks which appear in the chromatogram show spectral behaviour similar to that of standard catechins and proanthocyanidins.
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    HPLC of individual site glycoforms in serum orosomucoid (1991)
    Springer
    Chromatographia 31 (1991), S. 478-480 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Orosomucoid ; Complex glycans ; α1 glycoprotein ; Glycopeptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The glycoforms contained within each glycosylation site of orosomucoid can be separated by reverse-phase HPLC without removal of the associated peptide or chemical derivatization. The chromatographic properties of the glycopeptides are dominated by the peptide portion but modified by the hydrophilicity of the glycan in a regular manner depending on its size. Assignments for known structures are readily made, permitting quantitative assessment of changes in glycoform concentration at individual glycosylation sites.
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    Immunoaffinity precolumn for selective sample pretreatment in column liquid chromatography: Immunoselective desorption (1991)
    Springer
    Chromatographia 31 (1991), S. 469-477 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Immunoaffinity precolomn ; Oestrogens ; Bioanalysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An automated liquid chromatographic system is described using immunoaffinity precolumns for sample pretreatment. The system consists of a column-switching unit allowing preconcentration from a large volume of sample (e.g. 15 ml of urine) onto an immunoaffinity precolumn (containing polyclonal antibodies immobilized on Sepharose). After sorption, the analytes are desorbed by a mixture of two cross-reacting solutes, followed by reconcentration on a C-18-bonded silica precolumn, and then separation on a C-18-bonded silica analytical column. Using oestrogen steroids as model compounds and UV absorbance detection, the minimum detectable concentration is ca. 200 ng/l with a repeatability of 6–8%. The total analysis time is 45 min which allows the unattended analysis of 30 samples per day. The features of the sample pretreatment method, especially of the immunoselective desorption, are evaluated and the general applicability of the system is discussed.
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    Chromatographic optimization for the determination of traces of selenonium and arsonium cations by HPLC with on-line detection by AAS (1991)
    Springer
    Chromatographia 31 (1991), S. 481-488 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Selenonium and arsonium cations ; AAS detection ; Chromatographic optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Optimal mobile phase compositions were determined for the separation of selenonium ions [trimethylselenonium, (2-hydroxyethyl)dimethylselenonium and (2-acetoxyethyl)dimethylselenonium] and, separately, for arsonium ions (tetramethylarsonium, arsenobetaine, and arsenocholine) by HPLC with detection by atomic absorption spectrometry (AAS). Surface response methodologies were used to predict the variations in detector response (peak area), capacity factors, and selectivities as a function of the mobile phase composition. For selenonium analytes, a mixture of triethylammonium and trimethylsulfonium ions in the methanol-1% acetic acid mobile phase provided a compromise between resolving power and chromatographic efficiency. By contrast, optimum chromatography of the arsonium analytes was obtained by replacing onium additives in the mobile phase by picrylsulfonic acid. For both selenonium and arsonium analytes, the dominant interaction with the stationary phase was with residual silanols and improvements to the chromatographic performance of these analytes resulted in appreciable decreases in their limits of detection.
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    Flame ionization detection for the determination of the chemical composition distribution of non-UV absorbing copolymers (1991)
    Springer
    Chromatographia 31 (1991), S. 493-499 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Flame ionization detection ; Poly(styrene-co-methyl acrylate) ; Poly(methyl acrylate-co-n-butyl acrylate) ; Chemical composition distribution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This investigation is focused on the development of HPLC with subsequent flame ionization detection as a tool to determine the chemical composition distribution of non-or poorly UV absorbing copolymers. Experiments were carried out with poly(styrene-co-methyl acrylate) and poly(methyl acrylate-co-n-butyl acrylate) copolymers. HPLC combined with FID provided useful qualitative information. Quantitative information could be obtained after calibration.
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    Separation of glycated hemoglobin A1C by high-performance liquid chromatography on a non-porous exchanger (1991)
    Springer
    Chromatographia 31 (1991), S. 505-506 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Non-porous cation exchanger ; Hemoglobin A1C ; pH gradient elution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary High-performance ion exchange chromatography on a nonporous cation exchanger was examined for the separation of glycated hemoglobin. A standard sample of human hemoglobin was separated with salt or pH gradient elution. Glycated hemoglobin A1C was well separated from other hemoglobin variants in less than 10 minutes. pH gradient elution gave better resolution than salt gradient elution.
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    Packing meterials with surface barriers, controlled distribution and topography of ligands for sample clean-up and analysis of biologically active solutes in HPLC (1991)
    Springer
    Chromatographia 31 (1991), S. 507-511 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Restricted access packings ; Packings with surface barriers ; Sample clean-up of biologically active analytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Various types of, so-called, restricted access packings have been developed for sample clean-up and analysis of biologically active solutes by means of HPLC. The unique feature of these packings is that they prevent the access of matrix components such as protein whilst selectively retaining the drug components and their metabolites. This results from the fact that the particles of the packings possess a surface barrier for large solutes at the external or internal surface area and exhibit a controlled gradient in the chemical surface composition. They are grouped, according to their particle structures, into internal-surface reversed phases (ISRP), shielded hydrophobic phases (SHP), semi-permeable surfaces (SPS), dual zone phases (DZP) and mixed functional phases (MFP). The structural characteristics and the chromatographic properties of these packings are reviewwed, especially with regard to their use in the assaying of drugs.
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    Determination of carbonyl compounds in air by HPLC using on-line analyzed microcartridges, fluorescence and chemiluminescence detection (1991)
    Springer
    Chromatographia 32 (1991), S. 33-39 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Air analysis ; Dansylhydrazones of carbonyl compounds ; Chemiluminescence ; Fluorescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Sensitive and selective detection of dansylhydrazones of atmospheric carbonyl compounds (aldehydes and ketones) can be achieved using high performance liquid chromatography (HPLC) with fluorescence or chemiluminescence detection. The carbonyl compounds are derivatized by drawing air through small glass cartridges packed with porous glass particles impregnated with dansylhydrazine. After sampling, the contents of the cartridges are analyzed on-line by using a small plug of water (200 μL) to transfer and focus the hydrazone derivatives at the head of a HPLC column. Greatly increased sensitivity over traditional methods derives from 1) analysis of the entire contents of the sampling cartridge, and 2) detection by fluoresence or peroxyoxalate chemilum-inescence. Results are compared for photo-initiated and H2O2-initiated peroxyoxalate chemiluminescence. This novel and practical system enables the detection of sub-ppbv concentrations of formaldehyde, acetaldehyde, acetone and higher carbonyls in air using relatively short sampling times.
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    Use of a displacement model for solvent sorption to study non-specific selectivity in reversed-phase liquid chromatography (1991)
    Springer
    Chromatographia 32 (1991), S. 13-18 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Alkyl bonded phases ; Non-specific selectivity ; Hydro-organic mobile phases ; Retention of alkanoate esters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A thermodynamic equation is derived for the non-specific selectivity of alkyl bonded phases as a function of the mobile phase composition using a displacement mechanism to model the sorption of solvents into the bonded phase. The equation is used to calculate the thermodynamic parameters which characterize the incremental behavior of a hydrophobic group in ethyl alkanoate and methyl perfluoroalkanoate ester solutes chromatographed with water-methanol and water-acetonitrile mobile phases on both octyl and octadecyl bonded phases.
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    High performance liquid chromatography assay for alanine amino transferase (1991)
    Springer
    Chromatographia 32 (1991), S. 23-26 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enzyme assay ; Alanine amino transferase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An improved method of alanine-amino transferase determination is proposed. The reaction is carried out with alanine and 2-oxoglutarate as substrates and analysis is by HPLC on a reversed-phase chromatographic system using a C18 column and tetrabutylammonium phosphate in phosphate buffer (pH 7.0)-acetonitrile as mobile phase. The enzyme activity was determined by directly following the formation of pyruvic acid without employing any secondary reaction, which is necessary in the spectrophotometric method. The detection limit of pyruvic acid is 10 pmole μl−1 and the standard deviation for the enzymatic activity of standard solutions is 5.4%. Furthermore under the chromatographic conditions selected it is possible to detect the presence of some intermediate species.
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    High-performance liquid chromatographic determination of furfural and hydroxymethylfurfural in apple juices and concentrates (1991)
    Springer
    Chromatographia 32 (1991), S. 45-48 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Furfural ; Hydroxymethylfurfural ; Apple juice
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A rapid and sensitive method for determining 2-furaldehyde (FUR) and 5-hydroxymethyl-2-furaldehyde (HMF) in apple juices and juice concentrates has been developed. The method for FUR and HMF involves the solid-liquid extraction of the juice by using a C-18 cartridge prior to reversed-phase separation with detection at 280 nm. The mobile phase was acetonitrile-water (8/92, v/v) at a flow rate of 1.0 ml/min. Recoveries from apple juices and juice concentrates spiked at different levels ranged from 94.1 to 104.0 (FUR) and 94.5 to 100.5 (HMF). The quantification limit for both, FUR and HMF, was 5 ppb.
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    Sample-induced internal pH gradients in microcolumn liquid chromatography of proteins (1991)
    Springer
    Chromatographia 32 (1991), S. 61-64 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Sample-induced pH gradients ; Separation of proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The technique of an internal pH gradient induced by the sample is applied to the separation of proteins by liquid chromatography. Compatibility of the method with microcolumns is demonstrated and examples of separations on different types of sorbents are given.
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    Distribution behavior of some drug enantiomers in an aqueous two-phase system using counter-current extraction with protein (1991)
    Springer
    Chromatographia 32 (1991), S. 56-60 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Counter-current extraction ; Chiral resolution ; Ofloxacin enantiomers ; Aqueous two-phase system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The partial resolution of some drug enantiomers by counter-current extraction in an aqueous two-phase system using bovine serum albumin (BSA) or ovomucoid (OVM) as chiral discriminator is described. The phase system was prepared with dextran 40, polyethylene glycol and a protein. Ofloxacin (OFLX) enantiomer was well recognized by the BSA system, whereas the enantiomers of carvedilol (β-blocker) and DG-5128 (a new oral hypoglycaemic drug) were hardly recognized by the OVM system. The distribution coefficients of (S)-, (R)- and rac-OFLX varied with pH. Good enantioselectivity for OFLX was obtained at relatively high pH (≥ pH 9). The crude optically enriched OFLX enantiomers were extracted from the aqueous fractions and finally purified by thin-layer chromatography.
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    Evaluation of octadecyl-bonded alumina for separations of proteins and peptides by reversed-phase high-performance liquid chromatography (1991)
    Springer
    Chromatographia 32 (1991), S. 49-55 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Protein separations ; Peptide separations ; Octadecylalumina
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A recently-developed octadecyl-bonded alumina (ODA) stationary phase was evaluated for the separation of peptides and proteins by reversed phase high performance liquid chromatography. Using standard water-acetonitrile mobile phase gradients containing 0.1 % trifluoroacetic acid, the average peak capacity obtained for the separation of a mixture of ribonuclease a, cytochrome c, lysozyme and carbonic anhydrase on an ODA column are similar to that obtained on a widely used octadecylsilane (ODS) column. However, overall chromatographic resolution of the components of this mixture on ODA is inferior to that obtained on ODS. Cytochrome c peak areas were found to be ∼50% smaller on the ODA column than on ODS. On the other hand, both peak capacities and resolutions of octapeptide mixtures were found to be generally superior on the ODA column, and peak areas for a representative octapeptide were found to be virtually identical for both ODA and ODS columns. The differences in the results obtained on the ODA and ODS columns for these separations are attributed to the smaller pore size and unique fused-microplatelet shape of the ODA particles. Comparisons of the separations of the tryptic digest of cytochrome c on the ODS and ODA columns demonstrate that the ODA phase is potentially as useful as ODS for peptide mapping applications.
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    Analysis of enantiomeric flavanones in plant extracts by high-performance liquid chromatography on a cellulose triacetate based chiral stationary phase (1991)
    Springer
    Chromatographia 32 (1991), S. 69-72 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Enantiomeric separation ; Chiral stationary phase ; Cellulose triacetate ; Flavanones ; Plant extracts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Flavanones ofArachis hypogaea, Hemizonia increscens, Eriodictyon glutinosum andThymus vulgaris extracts have been stereospecifically analysed by gradient elution on a column of cellulose triacetate supported on silica gel diol. The stereochemistry of naringenin, eriodictyol and homoeriodictyol was in favour of the 2S-configurated flavanones.
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    Studies of the influence of hydrogen chloride on the liquid chromatographic properties of amino bonded phases (1991)
    Springer
    Chromatographia 32 (1991), S. 79-81 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Amino bonded phases ; Hydrogen chloride treatment ; Retention anomalies ; Normal-phase separations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The influence of hydrogen chloride on the retention properties of aminopropyl bonded phases is studied using a series of simple aromatics, phenols and acids. The result of the HCL treatment is to mediate the hydrogen bonding interaction between the solute's polar functional groups and the bound amino groups.
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    Ion-pair chromatography of dianionic species by dionium reagents (1991)
    Springer
    Chromatographia 32 (1991), S. 73-78 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair separations ; Dianionic species ; Dionium reagent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Dionium cations, polymethylenebis(tributylphosphonium)s (BuCnBPs), were used as ion-pair reagents for ion-pair chromatography of dianionic species, such as maleate, fumarate, phthalates, and naphthalenedisulfonates. The longer the length of methylene chain connecting the two phosphonium cationic ceterns within BuCnBP, the larger was the retention of these dianionic species. The dionium reagents had a higher retention ability compared to conventional monoonium reagents, and enabled a higher resolution among the dianionic species of structural isomers. The extraction behavior of the dianionic species in a loctanol/water system was also investigated. The retention behavior by the use of BuCnBP was discussed in comparison with the extraction behavior.
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    Enantioseparation of α-phenylglycine by HPLC on an ODS column coated with chiral crown ether (1991)
    Springer
    Chromatographia 32 (1991), S. 82-84 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chiral separation ; Chiral crown ethers ; Phenylglycine enantiomers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Previous work has demonstrated the possibility of crcating chiral stationary phases by coating a suitable support material via the mobile phase. The result is a wide variety of chiral phase systems which can be used in liquid chromatogrphy to separate enantiomers by a liquid-solid adsorption mechanism. The present paper demonstrates the potential of this technique for chiral crown ethers incorporating an α-D-mannopyranoside unit using the separation of phenyglycine enantiomers as an example.
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    Rapid separation of some antiepileptic drugs in serum by HPLC (1991)
    Springer
    Chromatographia 32 (1991), S. 85-86 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Antiepileptic drugs ; Optimised separation ; Serum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A fast and easy, iscratic high-performance liquid chromatographic method for the simultaneous determination of primidone, phenobarbital, phenytoin, carbamazepine and thiobutabarbital from serum samples has been developed. The optimal eluent composition is 36% acetonitrile, 24% methanol and 40% phosphate buffer. Using a programmable wavelength detector very low (sub-therapeutic) levels of the drugs can be measured.
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    URL: http://dx.doi.org/10.1007/BF02262474
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    Effect of inorganic salt concentration on the retention value in reversed phase ion-pair liquid chromatography (1991)
    Springer
    Chromatographia 32 (1991), S. 538-542 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair separation ; Salt concentration ; Charge number of solute ; Gouy-Chapman theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Thermodynamic and numerical treatments have been combined with Gouy-Chapman theory were to show that the effect of the salt concentration on the capacity factor in reversed-phase ion-pair liquid chromatography (RP-IPC) can be expressed as lnk′=A+blnCs. The parameter B is related to the charge number of the solute, and the parameter A is determined by both electrostatic and nonelectrostatic interaction, and can the linearly correlated with logarithm of the capacity factor in RP-HPLC for the solute with one negative charge. It also been observed that the electrostatic interaction is reduced with increasing salt concentration in RP-IPC, and this effect is more remarkable for solutes with more than the one negative charge of sulphonic acids.
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    URL: http://dx.doi.org/10.1007/BF02327899
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    Study of the efficiency of a mobile phase used in size-exclusion HPLC for the separation of peptides from a casein hydrolysate according to their hydrodynamic volume (1991)
    Springer
    Chromatographia 32 (1991), S. 499-504 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Size-exclusion ; Peptides ; Casein hydrolysate ; FAB-MS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A casein hydrolysate was eluted on a TSK G-2000 SW sizeexclusion high-performance liquid chromatography (SE-HPLC) column using a mobile phase which gives a correlation coefficient of 0.98 for the separation of 20 pure and synthetic peptides and proteins of molecular weight (M. W.) varying from 243.28 (Ala-Pro-Gly) to 43 000 (Ovalbumine) daltons. Further isolation and purification of peptides present in each of the 8 different fractions collected from the SE-HPLC were done by reversed-phase HPLC (RP-HPLC). Peptide experimental M. W. determined from the calibration curve obtained for synthetic or purified peptides was compared to their precise M.W. obtained by fast atom bombardment-mass spectrometry analysis (FAB-MS). The results do not show a separation of this complex hydrolysate by SE-HPLC according to the hydrodynamic volume of its constituents.
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    Applicability and precision of simultaneous chromatographic determination of some characteristics of solid phases and their beds (1991)
    Springer
    Chromatographia 32 (1991), S. 514-522 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Streaming current ; Specific pore volume and surface area ; Specific weight ; Bed porosity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The applicability and precision of the method allowing the determination of several characteristics of the sorbent and its bed from two simple chromatographic retention measurements were tested with porous metal oxides and some other solids. The typical time of one retention experiment is 1–3 minutes. The method was verified with chromatographic solid phases containing both mesopores and macropores. The agreement between the retention volume of the streaming current response, caused by the change in the concentration of the polar component of the binary hydrocarbon-based mobile phase, and the total volume of the liquid in the column is decisive for the applicability of the method. If the influence of the error in the determination of the sorbent's weight in the column and of the column tube's volume are neglected, the external and the total bed porosities and the specific weight of the sorbent can be determined with the relative error of the retention volume measurement. The error of the determination of the specific pore volume and internal bed porosity will be twice as much. The specific surface area can be determined approximately for sorbents with average and large surface areas.
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    URL: http://dx.doi.org/10.1007/BF02327896
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    High-performance liquid chromatographic assay of debrisoquine and its 4-hydroxy metabolite in human urine (1991)
    Springer
    Chromatographia 32 (1991), S. 523-526 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Debrisoquine ; Urine ; Phenotype
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An isocratic HPLC method is described. It allows the simultaneous determination of debrisoquine and 4-hydroxydebrisoquine in urine. Sample preparation involves a rapid and simple (one step) liquid-liquid extraction without derivatization. Separation, followed by UV-detection, is carried out on a nitrile column in reversephase mode with a binary, aqueous mobile phase. This rapid assay uses a new internal standard (guabenxane) and allows the determination of urinary concentrations with good precision and appropriate sensitivity.
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    URL: http://dx.doi.org/10.1007/BF02327897
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    Elution behavior of N-heterocyclic derivatives of mixed ruthenium(II)-sulfoxide complexes in reversed-phase high-performance liquid chromatography (1991)
    Springer
    Chromatographia 32 (1991), S. 546-548 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ruthenium mixed complexes ; Sulfoxides ; N-Heterocyclic bases ; Hydrophobic properties of aromatic ligand
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The elution behaviour of a series of dichlorobis-(dimethylsulfoxide)bis(N-heterocyclic)ruthenium(II) complexes has been investigated using reversed-phase HPLC. Similar trends as those displayed by the free N-heterocyclic bases have been observed for the complexes, essentially reflecting the hydrophobic properties of the aromatic ligands.
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    Sample preparation by supercritical fluid extraction in environmental food and polymer analysis (1991)
    Springer
    Chromatographia 32 (1991), S. 527-537 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Supercritical fluid chromatography ; Supercritical fludi extraction (SFE) ; Explosives ; Cholesterol ; Polymer additives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Extraction with supercritical CO2 is a versatile method for sample clean-up and trace enrichment. The off-line coupling of SFE and HPLC is used to determine various explosives in debris as well as pesticides in soil. In food analysis the metod could be applied to determine cholesterol in noodles quantitatively. Correlations between the retention in RP chromatography and required extraction conditions could the established. The higher the organic modifier concentration in the eluent has to be, the smoother the extraction conditions required. With the non-volatile solutes studied, extraction temperature had no influence on extraction yield and speed. On-line coupling of SFE and capillary SFC is a very convenient and sensitive method for the determination of polymer additives. The coupling device described can also be used for “solventless” injection in capillary SFC.
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    Reverse-phase HPLC of organic acids in musts (1991)
    Springer
    Chromatographia 32 (1991), S. 555-558 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Organic acids ; Grape musts ; Direct injection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A simple method for reverse-phase HPLC analysis of organic acids present in must has been developed. It is carried out in isocratic conditions, with a weak dilute acid as eluent and U.V. detection. The aim is to minimize sample preparation merely to filtration: direct injection is proposed as an approach toin vivo conditions.
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    Optimization of isocratic mobile phase composition for HPLC analysis of eleven substituted phenols (1991)
    Springer
    Chromatographia 32 (1991), S. 566-572 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Isocratic Optimization ; Overlapping Resolution mapping method ; Substituted Phenols
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The Overlapping Resolution Mapping (ORM) method has been applied to predict the best mobile phase composition for the separation of eleven substituted phenols. This separation was carried out by HPLC using reversed-phase isocratic elution and UV detection with a diode array detector. The effect of temperature on the separation process was also taken into account. The optimized method was applied to identify phenols in waste and drinking water.
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    A computer routine for the selection and optimization of multisolvent mobile phase systems in reversed-phase liquid chromatography (1991)
    Springer
    Chromatographia 32 (1991), S. 559-565 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Multisolvent mobile phase ; Optimization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A computer program is described for the optimization of reversed-phase multisolvent separations. After four initial gradient runs are carried out, calculation will locate a possible optimum with binary systems or select two binary mixtures with respect to both the analysis time and the selectivity. In this latter case, two additional experiments will locate the true optimum on a straight line joining these two binary compositions on the solvent triangle (ternary system). The efficiency of this procedure is demonstrated with an illustrative example.
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    Separation of copoly(styrene/acrylonitrile) samples according to composition under reversed phase conditions (1991)
    Springer
    Chromatographia 32 (1991), S. 107-112 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Styrene/acrylonitrile polymers ; Gradient elution ; Solubility effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Copoly(styrene/acrylonitrile) samples (S/AN) have been repeatedly separated according to composition by gradient HPLC with alkane hydrocarbons as a starting eluent A and dichloromethane (DCM) or tetrahydrofuran (THF) as a solvent B. In these systems, retention increased with AN content of the copolymers. The chemical nature of the column packings used had almost no influence on the retention of S/AN samples. The present paper shows thatn-pentane andn-heptane, when used in a given volumetric gradient with DCM+20% methanol as a solvent B, lead to identical solution characteristics of S/AN on silica columns. A similar result was obtained on C18 columns withn-heptane or cyclohexane, whereas gradient elution with toluene as a starting eluent caused insufficient resolution. Reversed phase separation of S/AN copolymers could be achieved on polystyrene gel columns through gradients with methanol as a starting eluent and DCM or THF as a solvent B. In both systems, retention decreased with increasing AN content of the copolymers. The elution characteristics were almost linear in the range 0–20 wt% AN. This behaviour can be understood in the context of polymer solubility: in both systems, the solubility borderline of S/AN has a distinct maximum at about 25 wt% AN. Reversed phase separation was achieved at the lefthand slope of these curves where the dissolution of a sample with a higher AN content requires less DCM or THF solvent than the dissolution of copolymers which are poorer in AN. This idea predicts that samples with more than 25 wt% AN should elute later than S/AN whose composition is near to the solubility maximum. This indeed was found with a copolymer containing 36.2 wt% AN.
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    URL: http://dx.doi.org/10.1007/BF02325011
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    Improved HPLC methodology in occupational exposure studies on formaldehyde (1991)
    Springer
    Chromatographia 32 (1991), S. 113-115 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Formaldehyde in air ; Dinitrophenyl hydrazine ; Occupational hygiene studies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary This work describes an HPLC method for the determination of formaldehyde concentration in air. Traps containing 20–40 mesh silica gel coated with 2,4-dinitrophenylhydrazine (DNPH) are used. After aspiration of air the traps are eluted with methanol. The hydrazone formed is then separated on a C18 column using a mobile phase of methanolwater (50–50 v/v). The effluent is monitored with a UV detector at 365 nm. To calibrate and to compare this method with that of Niosh 2502 (traps coated with 2 benzylamino ethanol on Chromosorb 102), a mixing chamber that generated atmospheres of known concentration of formaldehyde was used.
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    Identification of by-products in phenylisocyanate pre-column derivatization by thermospray liquid chromatography-mass spectrometry (1991)
    Springer
    Chromatographia 32 (1991), S. 125-129 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Phenylisocyanate derivatization ; By-products of derivatization ; Thermospray LC/MS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Thermospray liquid chromatography-mass spectrometry has been applied to the identification of by-products in precolumn derivatization by phenylisocyanate. These byproducts are eluted early in the same chromatographic region as the low molecular weight derivatives and were located by chromatographic analysis of a blank sample. Their identification would offer further qualitative information in the use of phenylisocyanate as a derivatizing agent. Five compounds resulted from the reaction of phenylisocyanate and the reaction medium were identified: two from a reaction between phenylisocyanate and methanol, two from the reaction between phenylisocyanate and water, and one from the polymerisation of phenylisocyanate.
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    Determination of micelle-solute association constants of some benzene and naphthalene derivatives by micellar high-performance liquid chromatography with butanol and sodium chloride additives to mobile phase (1991)
    Springer
    Chromatographia 32 (1991), S. 148-154 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Micelle-solute association constants ; Benzene and naphthalene derivatives ; Butanol and NaCl additives
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The interaction between some benzene and naphthalene derivatives and sodium dodecyl sulphate and hexadecyltri-methylammonium bromide in the presence of n-butanol and sodium chloride has been evaluated by high-performance liquid chromatography using micellar mobile phases. Micelle-solute association constants are given for the compounds investigated. The results show that addition of n-butanol to the mobile phase decreases the association constant values relative to those in the absence of any additive. Conversely, when sodium chloride is added to the mobile phase, an increase of the association constant is obtained in most cases. Good correlation between free energy of transfer for water-micelles and for octanol-water has been observed.
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    Dependence of the retention volumes of additional streaming current responses and of the column void volume on mobile phase composition (1991)
    Springer
    Chromatographia 32 (1991), S. 130-136 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Streaming current ; Column interparticle volume ; Column void volume ; Column hold-up volume
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The influence of the alcohol content of the mobile phase and water, acetic acid and aniline as mobile phase additives on the generation and shape of two additional changes of the streaming current, generated inside the liquid chromatography column by injection of any sample and recorded before the responses of retained solutes, was studied in a normal-phase system using silica gel as the stationary phase. The mobile phases were based on a n-heptane-1-propanol mixtures. Under the same conditions the relationships between the column interparticle volume, the column void volume and the total liquid volume in the column and the retention volumes of these two streaming current responses, having the form of chromatographic peaks, were studied. The column void volume was identified with the retention volume of n-octane. The total liquid volume in the column (column hold-up) was calculated from the weight loss of the column wetted with water at first and then dried in nitrogen stream. The retention volume of the first streaming current response equals the column interparticle volume disregarding the mobile phase composition. If the 95∶5 n-heptane-1-propanol mobile phase contains water up to 80% of its saturated concentration (up to 0.114% by vol.), the retention volume of the second response agrees with the total volume of the liquid in the silica gel column, with a precision better than 2%. At a higher relative water saturation the retention volume of the second response increases, while the column void volume decreases. Both changes are explained by the spontaneous formation of a highly polar stagnant liquid in the pores of the silica gel.
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    Liquid chromatography of erythromycin A and related substances on poly(styrene-divinylbenzene) (1991)
    Springer
    Chromatographia 32 (1991), S. 162-166 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Erythromycin A and related substances ; Poly(styrene-divinylbenzene)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An isocratic liquid chromatography method for assay and purity control of erythromycin is presented. Erythromycin A is separated from all its potential impurities, except erythromycin D. The selectivity depends on the pore size of the poly(styrene-divinylbenzene) stationary phase. Wide pore PLRP-S 8 μm 1000 Å shows the best selectivity. The column is heated at 70°C. The mobile phase is acetonitrile-2-methyl-2-propanol-0.2 M potassium phosphate buffer pH 9.0-water (3:16.5:5:75.5). The flow rate is 2 ml/min. UV detection is performed at 215 nm. The total analysis time is about 30 min. The method was used to compare official standards.
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    Poly(methylglutamate)-coated surfaces in HPLC and CE (1991)
    Springer
    Chromatographia 32 (1991), S. 171-178 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Capillary Electrophoresis ; Surface Coating ; Poly(methyglutamate)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Thermal polymerization of the N-carboxyanhydride of glutamic acid-5-methylester was used to coat microparticulate silica and the surface of capillaries with poly(methylglutamate) (PMG). By increasing the thickness of the PMG layer the hydrophobicity of the stationary phases could be increased. However, total shielding of surface silanols was not achieved. The PMG-coated silicas for HPLC showed unexpected and strange behavior in the chromatography of proteins. Nevertheless, capillaries coated with PMG proved to be excellent for highly efficient CE separations of proteins at medium pH values.
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    Porous copolymer-based cation exchanger for the off-line preconcentration of aromatic amines from water (1991)
    Springer
    Chromatographia 32 (1991), S. 167-170 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Porous copolymer-based cation exchanger ; Solid-phase extraction ; Aromatic amines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A weakly polar porous copolymer and the sulfonic acid cation exchanger based on this copolymer were tested as sorbents for off-line preconcentration of aromatic amines from water. Minicolumns packed with the 1,4-di(methacryloyloxymethyl)naphthalene—divinylbenzene copolymer and the cation exchanger were used for the solid-phase extraction of polar amines. In order to study the sorption properties of these polymeric materials, the recoveries and breakthrough volumes ofp-aminophenol,o, m andp-phenylenediamine, aniline,o andp-anisidine,p-nitroaniline, ando-toluidine were determined.
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    An application of fast protein liquid chromatography (FPLC) in the purification of retinol binding protein from rat serum (1991)
    Springer
    Chromatographia 32 (1991), S. 229-232 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Affinity chromatography ; SDS-PAGE ; Ultrafiltration ; Retinol binding protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retinol Binding Protein (RBP) is the specific plasma protein for the transport of retinol from liver to peripheral tissues. It is a single polypeptide chain of approximately 21 KDa, and circulates as a 1∶1 molar complex with transthyretin (TTR). The relative low concentration in plasma (40–50 μg/ml and its chromatographic behaviour on ionic exchangers render the purification of rat RBP particularly laborious. In this paper we report a simple and semi-automatic method for the preparative purification to homogeneity of rat serum RBP. The method includes: (1) Selective removal of albumin by affinity chromatography on a Blue Sepharose column; (2) Chromatography on a Mono Q strong anion exchange column; (3) Dissociation of the RBP-TTR complex by 3 M urea; (4) Concentration, desalting and freeze drying. The purified RBP has been used for the production in rabbit of antirat RBP specific antibodies for studies on nutritional control of RBP synthesis and metabolism.
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    Retention behavior of some monobasic penicillins and their quaternary ammonium ion pairs in reversed-phase high-performance liquid chromatography (1991)
    Springer
    Chromatographia 32 (1991), S. 436-440 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pair chromatography ; Quaternary ammonium ion pairs ; Penicillins ; Retention behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention behavior of some monobasic penicillins (penicillin G, penicillin V, oxacillin, cloxacillin and dicloxacillin) and their quaternary alkylammonium ion pairs has been studied in a reversed-phase high-performance liquid chromatographic system using Partisil 5 μm ODS-3 asstationary phase and mixtures of acetonitrile and aqueous phosphate buffers as mobile phases. The influence of pH, pairing-ion chain length and concentration, and column temperature on retention has been investigated and the observed behavior of the compounds during the chromatographic process has been discussed.
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    A quantitative study of the adsorption effect on the retention of dicarboxylic acids in ion-exclusion chromatography (1991)
    Springer
    Chromatographia 32 (1991), S. 453-456 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-exclusion ; Retention ; Adsorption effects ; Dicarboxylic acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Retention values and distribution coefficients for C4−C9 dicarboxylic acids on a column packed with cation exchange resin in the H+ form were determined, using dilute HCl solution as eluent. Based on the Donnan membrane equilibrium and adsorption equilibrium, adsorption coefficients were evaluated, and the adsorption contributions to the retention of these analytes were estimated.
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    Determination of polar pollutants in water using an on-line liquid chromatographic preconcentration system (1991)
    Springer
    Chromatographia 32 (1991), S. 445-452 
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    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; On-line preconcentration ; Polar pollutants ; Water (tap and surface)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An isocratic column liquid chromatographic system with UV absorbance detection at 230 nm has been developed for the rapid trace-level determination of a large number of polar pollutants in water. The systems contains two precolumns, in series, which are packed with a styrenedivinylbenzene (PLRP-S) polymer. The second precolumn is also loaded with sodium dodecylsulphate before use. Each precolumn is combined with a PLRP-S analytical column, and aqueous acetonitrile mixtures (pH 3) are used for the separation of neutral as well as acidic and basic pollutants. With 10-ml water samples the detection limits for all analytes, in tap water, are in the low to sub μg/l range. Relevant analytical data are reported and the advantage of using a dodecylsulphate-loaded precolumn over a cation-exchange precolumn is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02327976
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    Electronic Resource
    Determination and quantification of dimethyl sulphoxide by HPLC (1991)
    Springer
    Chromatographia 32 (1991), S. 461-462 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; DMSO in water and wastewater
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A high-performance liquid chromatographic method has been developed for detecting and quantifying dimethyl sulphoxide (DMSO) in water and especially in wastewater. The detection limit for the quantification of DMSO is 0.5 ppm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02327979
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