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  • 1
    Electronic Resource
    Electronic Resource
    Retention of some ring-substituted aniline derivatives by porous graphitized carbon. Dependence on physico-chemical parameters (1992)
    Springer
    Chromatographia 33 (1992), S. 356-360 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Porous graphitized carbon ; Ring-substituted aniline derivatives ; Electronic interactions ; Principal component analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention characteristics of 22 aniline derivatives were determined on a porous, graphitized-carbon column in unbuffered acetonitrile-water and methanol-water mixtures. Each aniline derivative gave symmetrical peaks in each eluent without buffers. Good linear correlations were found between the log k′ and the concentration of the organic component in the eluent. The slope and intercept values differed according to the type of organic modifier and the charcter, number and position of substituents, indicating the different selectivities of methanol and acetonitrile and the good separating power of the column. Multivariate mathematical-statistical calculations proved that the retention of ring-substituted aniline derivatives is mainly governed by electronic parameters and the hydrogen acceptor capacity of substituents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275918
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  • 2
    Electronic Resource
    Electronic Resource
    Retention characteristics of an aluminium oxide HPLC column (1990)
    Springer
    Chromatographia 29 (1990), S. 593-596 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Alumina adsorbent ; Substituted anilines ; Retention data
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention of 29 aniline derivatives was determined by high performance liquid adsorption chromatography using an alumina column and dichloromethane-n-hexane mobile phases in various vol. ratios. The retention parameters of anilines (log k′ and the slope and intercept value of the correlation between log k′ and the dichloromethane concentration in the eluent) were correlated with the physicochemical parameters (lipophilicity and adsorption capacity of silica) of aniline derivatives. The retention of anilines decreased with their increasing lipophilicity and increased with their increasing silica adsorption capacity. The alumina columns was found to be an appropriate support for the adsorptive phase separation of polar compounds as aniline derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02261229
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of nature of support and impregnating agent on lipophilicity determination for nonionic surfactants by reversed-phase thin-layer chromatography (1991)
    Springer
    Chromatographia 31 (1991), S. 152-156 
    Details
    ISSN: 1612-1112
    Keywords: Thin-layer chromatography ; Nonylphenyl ethylene oxide oligomers ; Lipophilic solid phases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention of 9 nonylphenyl ethylene oxide oligomers was determined in 15 reversed-phase chromatographic systems using silicone oils of various molecular mass as impregnating agents and silica, cellulose and alumina supports. The data were evaluated with principal component analysis carried out on the covariance and the correlation matrices. The RM values did not follow the additivity rule and they did not change linearly with increasing length of the ethylene oxide chain. This is probably due to the folded state of the chain in the eluent. The molecular mass of the silicone oils had a negligible effect on the retention whereas the retention increased with increasing level of impregnation. The support considerably influenced the lipophilicity values of these nonionic surfactants and cellulose seemed to be the most appropriate support. Calculations proved that the application of a correlation matrix may cause data distortion; therefore, the use of a covariance matrix is strongly proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274564
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of various salts on the reversed-phase retention of some dansylated amino acids in TLC (1993)
    Springer
    Chromatographia 36 (1993), S. 302-306 
    Details
    ISSN: 1612-1112
    Keywords: Thin-layer chromatography ; Dansylated amino acids ; Salting-out effect ; Alkali metal chlorides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention of 14 dansylated amino acid derivatives was determined using aqueous LiCl, NaCl, KCl, RbCl and CsCl solutions as eluents in reversed-phase thinlayer chromatography. The salts exerted typical salting-out effects, the retention of each dansylated amino acid increased with increasing concentration of salt in the eluent. This effect has been tentatively explained by the suppression of the dissociation of the polar groups in the solute molecules resulting in increased apparent lipophilicity. The correlation between the increased retention of dansyl amino acids and the salt concentration was found to be linear. The hydrated radii and energy of hydration of cations as well as the hydrophobicity of free amino acids and the pK value of the α-amino groups simultaneously influenced the retention.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02263882
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  • 5
    Electronic Resource
    Electronic Resource
    Determination of the lipophilicity of some anti-hypoxia drugs: Comparison of TLC and HPLC methods (1993)
    Springer
    Chromatographia 35 (1993), S. 275-280 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Thin-layer chromatography ; Anti-hypoxia drugs ; Lipophilic character and retention
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The lipophilicity of 14 anti-hypoxia drugs has been determined by reversed phase thin-layer (RPTLC) and reversed phase high performance liquid chromatography (RPHPLC) in eluent systems containing different concentrations of acetonitrile and potassium dihydrogen phosphate. There was significant correlation between lipophilicity and the specific hydrophobic surface area of the drugs in RPTLC, indicating that the drugs behave as an homologous series of compounds. In RPTLC the concentration of buffer has a negligible effect on the retention of the drugs whereas in RPHPLC the buffer concentration influenced the retention. This discrepancy can be explained by the lower sensitivity of RPTLC. There was strong correlation between lipophilicity values determined by both methods, proving that both are suitable for the determination of molecular lipophilicity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02277509
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of some new polysiloxane stationary phases by principal component analysis (1994)
    Springer
    Chromatographia 38 (1994), S. 227-231 
    Details
    ISSN: 1612-1112
    Keywords: Gas chromatography ; Stationary phase characterization ; Principal component analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary In this study, several new stationary phases were characterized by principal component analysis. Fourteen new stationary phases, including substituted phenyl and oligoethyleneoxide functionalities on polysiloxane polymers, were tested and compared to three well known stationary phases. The main features of these phases were studied using a series of test solutes of varying chemical characteristics representing the data set for principal component analysis. Two principal compounds were found to account for 99.20% of the variance (the first accounted for 94.96% and the second for 4.24%). The data were represented as a two-dimensional map for visual representation of the characteristics of these stationary phases. The first principal component represented a selectivity based on polarity (r2=0.998), while the second showed Lewis acid-base characteristics of the phases. Polarizable and amphoteric characteristics of these phases also became evident using this evaluation method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290341
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  • 7
    Electronic Resource
    Electronic Resource
    Chromatographic methods (1990)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 337 (1990), S. 60-72 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00325724
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  • 8
    Electronic Resource
    Electronic Resource
    Interaction of diquat and paraquat with humic acid and the influence of salt concentration and pH on the strength of interaction (1993)
    Springer
    Fresenius' Zeitschrift für analytische Chemie 345 (1993), S. 541-544 
    Details
    ISSN: 1618-2650
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The interaction of the herbicides diquat and paraquat with humic acid and the influence of various salts and pH on the strength of interaction was studied by charge-transfer chromatography. Interactions between humic acids and both herbicides, probably by complex formation, were confirmed; they were stronger with paraquat than with diquat. The complex formation makes the herbicides more hydrophilic, facilitating their movement on cellulose surface. Salts in the environment significantly decreased the strength of interaction, indicating the hydrophilic character of the interactive forces. The charge of the cation also influenced the strength of interaction whereas the effect of ion radii was negligible. The effect of pH was lower than that of salt concentration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00326348
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  • 9
    Electronic Resource
    Electronic Resource
    Comparison of the retention behaviour of phenol derivatives on porous graphitized and octadecylsilica columns (1993)
    Springer
    Chromatographia 36 (1993), S. 19-26 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Structure-retention relationships ; Mathematical data analysis ; Phenol derivatives ; ODS and graphitized carbon columns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention of 22 ring-substituted phenol derivatives on porous graphitized carbon (PGC) (eluents: acetonitrile — water and methanol — water mixtures) and on octadecylsilica (ODS) (eluents: methanol — 0.025 M KH2PO4 mixtures) was determined, and the relationship between retention and physicochemical parameters were evaluated by principal component analysis followed by two-dimensional nonlinear mapping and by cluster analysis as well as by canonical correlation analysis. Calculations proved that marked differences can be detected between the retention characteristics of PGC and ODS columns, and the electronic parameters of phenol derivatives have the highest impact on their retention. The comparison of various multivariate mathematical-statistical methods indicated that principal component analysis followed by two dimensional non-linear mapping is the most appropriate method for the evaluation of large data matrices in RP-HPLC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02263830
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Reversed-phase thin-layer chromatography of various pesticides in the presence of water-soluble beta-cyclodextrin polymer (1994)
    Springer
    Chromatographia 38 (1994), S. 509-513 
    Details
    ISSN: 1612-1112
    Keywords: Thin-layer chromatography ; Commercial pesticide ; Water-soluble β-cyclodextrin polymer ; Salting-out effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The modification of the hydrophobicity of 28 commercial pesticides with a water-soluble β-cyclodextrin polymer (SCDP) in the presence of aqueous NaCl has been studied by reversed-phase thin-layer chromatography. The pesticides formed inclusion complexes with SCDP and these complexes are less lipophilic than the parent pesticides. The sodium chloride exerted a typical saltingout effect, the retention of each pesticide increased with increasing concentration of the salt in the eluent. This effect can be tentatively explained by the suppression of the dissociation of the polar groups in the solute molecules resulting in increased apparent lipophilicity. The correlation between lipophilicity and salting-out effect was found to be significant, that is the salting-out effect increases with increasing polarity (lower lipophilicity) of the pesticides, whereas the lipophilicity has negligible influence on the inclusion-forming capacity of non-homologous series of pesticides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02269844
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