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  • 1
    Electronic Resource
    Electronic Resource
    Influence of pressure on sorption equilibrium: HPLC column packing-mixed eluent (1984)
    Springer
    Chromatographia 18 (1984), S. 668-672 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Mixed eluents ; Preferential sorption of eluents ; Pressure effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Pronounced base line perturbations were repeatably observed in LC both in alternating recycling and in backflushing experiments when binary eluents and refractometric detectors were used. The perturbations which we call eigenzones appeared immediately after operating the recycling or the backflushing valve, and their size and shape depended on the nature of both the column filling and the mixed mobile phase as well as on the pressure drop across the column. Experimental results presented confirm that the primary causes of the eigenzones were the pressure changes in the columns which influenced the sorption equilibrium of mixed eluent components within the column packing. Some practical consequences of this effect are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02265811
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  • 2
    Electronic Resource
    Electronic Resource
    Polymers immobilized on silica gels as stationary phases for liquid chromatography (1993)
    Springer
    Chromatographia 37 (1993), S. 549-561 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Stationary phases ; Polymer-coated silica ; Polymer-filled silica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A variety of stationary phases for HPLC can be prepared by immobilization of organic polymers on silica gels. Such silica-polymer adsorbents combine the strength of an inorganic matrix with the selectivity and chemical inertness of organic resins. Moreover, effective shielding of residual silanols and the increase of column packing stability can also be achieved by modification of silica gels with organic polymers. There are two main approaches to the preparation of such composite sorbents. The first includes various routes for coating the silica surface with a polymer layer and the second is by filling the silica pores with a polymer network. A survey of polymers immobilized on silica gels and of various experimental procedures which can be used for composite sorbent synthesis is given in this review.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275796
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  • 3
    Electronic Resource
    Electronic Resource
    Liquid chromatography of polymer mixtures by a combination of exclusion and full adsorption mechanisms. Three- and four-component polymer blends (1998)
    Springer
    Chromatographia 48 (1998), S. 65-70 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Multicomponent mixtures ; Separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Coupling of full adsorption-desorption and size-exclusion chromatography (FAD-SEC) has been applied to the separation and molecular characterization of three- and four-component polymer blends. The method is based on the full adsorption of alln orn−1 components of the polymer blend in a specially designed FAD minicolumn. By appropriate eluent switching the adsorbed polymers are desorbed stepwise from the FAD minicolumn into an on-line SEC column for molecular characterization. It is shown that the desorption isotherms of particular blend components give valuable information about the appropriate displacer composition. The exact position of the desorption isotherms depends, however, both on the amount of polymer adsorbed and in the presence of other, chemically different, polymers within FAD column. The nature and composition of the displacer must, therfore, be adjusted if the intervals between the desorption of particular blend components are to be large enough to prevent displacement overlap.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02467518
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  • 4
    Electronic Resource
    Electronic Resource
    Evaluation of various bonded-phase materials for the off-line clean-up procedure of urinary 5-hydroxyindolacetic acid prior to its determination by HPLC (1986)
    Springer
    Chromatographia 22 (1986), S. 299-302 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chemically bonded phases ; Off-line prepurification ; Urinary 5-hydroxyindolacetic acid ; Electrochemical detection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Determination of serotonin (5-hydroxytryptamine, 5-HT) and its main metabolite, 5-hydroxyindolacetic acid (5-HIAA), became important in clinical chemistry. Commercially available and newly synthetised bonded-phase materials were evaluated in the off-line clean-up procedure of urine samples prior to the determination of 5-HIAA by high-performance liquid chromatography using electrochemical detection. From the point of reproducibility and recovery the best results were obtained employing our newly synthetised material consisting of silica gel support with wide pore diameter (≥20 nm) and large pore volume (≥2.5 cm3 g−1) with a mean (B.E.T.) surface area of 196m2 g−1. It has been modified by mixed chemically bonded C16−C18 phase. The achieved surface carbon coverage was 14.7% C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02268778
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  • 5
    Electronic Resource
    Electronic Resource
    Preparation of silanized silica with high ligand density. The effect of silane structure (1987)
    Springer
    Chromatographia 23 (1987), S. 442-446 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Chemically bonded phases ; Kinetics of silanization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A wide-pore silica for HPLC with a particle size of 7.5 μm, specific surface area of 360m2/g, pore diameter of 20 nm and pore volume of 2.1 cm3/g was silanized with n-octadecyldimethyl-chlorosilane (ODMCS), n-octadecyldimethylmetoxysilane (ODMMS) and n-octadecyldimethyl-dimethylaminosilane (ODMAS), in sealed glass ampoules. The ligand density obtained with an excess of ODMCS and ODMMS was found to be limited by reaction equilibrium; at low (〈50%) conversion of the surface silanols, the reaction displays pseudo-first-order kinetics. Silanization with ODMAS, which seems to be sterically controlled at higher conversions, yields a relatively high concentration of bonded octadecyl ligands (4.24μmol/m2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02311822
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  • 6
    Electronic Resource
    Electronic Resource
    Silica gel and carbon column packings for use in high-performance liquid chromatography (1990)
    Springer
    Chromatographia 30 (1990), S. 582-590 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Column packings ; Silica gel ; Porous carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The basic properties of the most important groups of HPLC column packings are briefly compared. The physical properties of totally porous silica and carbon-based sorbents, especially the pecularities of their pore structure, are discussed in more detail. The advantages of the sponge-like sorbent structure over a corpuscular structure are elucidated. The unconventional concept of pellicular sorbents with a thick porous layer and, especially, the concept ofsuperficially crazed sorbents is presented. Besides pores of the sizes that are necessary for the particular application in HPLC, the latter material also contains large and relatively deep cracks with widths two to five times larger than the specific mean pore diameters. An experimental crazed silica gel is presented and some of its chromatographic properties are shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269808
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  • 7
    Electronic Resource
    Electronic Resource
    Pressure jumps due to flow interruptions as source of system peaks in liquid chromatography with mixed eluents (1989)
    Springer
    Chromatographia 28 (1989), S. 189-192 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Pressure effects ; System peaks ; Sorption equilibrium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Brief pressure changes take often place within a liquid chromatography column, e.g., during sample injection. It is shown that pressure jumps may cause local changes in the composition of a mixed effluent and the rise of system peaks in the chromatogram. This is a consequence of the dependence of sorption equilibrium on pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02319645
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