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  • 1
    Electronic Resource
    Electronic Resource
    Effects of organic modifier and ion-pair reagent in liquid chromatography (1993)
    Springer
    Chromatographia 35 (1993), S. 390-394 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Electrostatic model ; Ion-pair reagent ; Organic modifier ; Prediction of k′ values
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The capacity factors of phenylamine and naphthylamine sulphonic acids in reversed-phase, ion-pair liquid chromatography (RP-IPC) were measured. The combined effects of organic modifier (Cb) and ion-pair reagent concentration (Cp) on retention follow an equation based on the electrostatic model: $$\ln k' = a + b lnC_p + cC_b $$ the experimental value of b correlates well with the value of 0.5 z (z=charge on analyte ion) predicted for mono and divalent ions. The measured value of b is, however, lower than that predicted for trivalent ions, which may be due to the effective number of charges being less than the apparent number. The absolute values of a and c are much larger than those in RP-HPLC in the absence of an ion-pair reagent, quantitative correlation of a and c with retention values in RP-HPLC and solute charges has been observed and a good linear relationship between a and c has been obtained, strongly supporting the validity of the electrostatic retention model. A critical value, R, at which the negative effect of methanol on retention is equal to the positive effect of the ion-pair reagent (TBAI) has been proposed. The critical values obtained are related to the behaviour of the solute, the ion-pair reagent and the stationary and mobile phases, and lies between −0.04 and −0.065 in most cases, which means that the increase by exp times (=2.718×) the ion-pair concentration the original is equivalent to a decrease of 0.04–0.065 in volume fraction of methanol
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02278591
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of inorganic salt concentration on the retention value in reversed phase ion-pair liquid chromatography (1991)
    Springer
    Chromatographia 32 (1991), S. 538-542 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02327899
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Role of solute hydrophobicity and charges in reversed-phase ion-pair liquid chromatography (1991)
    Springer
    Chromatographia 32 (1991), S. 329-333 
    Details
    ISSN: 1612-1112
    Keywords: Ion-pair chromatography ; Solute charges ; Solute hydrophobicity ; Quantitative correlation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The Logarithm of capacity factor in RP-HPLC and solute charges have been selected as descriptors of solute hydrophobicity and electrostatic interaction respectively. It has been observed that the logarithm of capacity factors (ln k ip ′ ) for a solute with one, two and three negative charges in RP-IPC can be well correlated with the logarithms of capacity factors (ln kR p ′ ) in RP-HPLC and solute charges (ne). Both the solute hydrophobicity and solute charges with opposite sign to those of the ion-pair reagent made a positive contribution to retention in RP-IPC. The logarithm of capacity factor linearly decreases with organic modifier concentration (Cb) and the logarithm of the inorganic salt concentration (lnCs). The intercept (ln k ip ′ , A) and slope (cip,B) values of a linear relationship between ln kR p ′ vs. Cb and ln k ip ′ vs. ln C5 also can be well correlated with ln kR p ′ and ne. The solute hydrophobicity and solute charges also made a positive contribution to the parameters ln k ip w and A, but a negative contribution to parameter cip. The parameter B, however is mainly determined by the solute charges.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02321429
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Combined effect of organic modifier concentration and column temperature on retention in reversed-phase ion-pair liquid chromatography (1992)
    Springer
    Chromatographia 34 (1992), S. 14-18 
    Details
    ISSN: 1612-1112
    Keywords: Column liquid chromatography ; Ion-pairing ; Temperature effects ; Organic modifier concentration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The retention behavior of phenylamine and naphthylamine sulphonic acid was evaluated in reversed-phase ion-pair liquid chromatography as a function of organic modifier concentration and column temperature. It has been observed that the logarithm of capacity factors decrease linearly with organic modifier concentration, and there is a good linear relationship between the intercept and slope for this relationship. Phenylamine and naphthylamine sulphonic acid retention decreases with increase in column temperature. A linear dependence of lnk ip ′ on the reciprocal of the absolute temperature, the Van't Hoff plot, was observed over the column temperature range studied, and the standard enhalpic change (ΔHo) for these sulphonic acid transfers from the mobile phaser to the stationary phase was determined. ΔHo was dependent on the solute structure and in the range from 2.5 Kcal/mol to 5.5 Kcal/mol, which is close to that observed in RP-HPLC. The enthalpy/entropy compensation effect was evaluated by plotting lnk ip(T) ′ vs. −ΔHo, and the apparent differences in retention mechanisms between the analytes were observed, which may arise from the significant differences in their configuration, hydrophobicity and the charges of the solutes as well as the complex retention processes of RP-IPC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02290452
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    Paper (German National Licenses)
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