Potentiometric determination of the second-stage dissociation constant of N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid in various water + organic solvent mixtures

1993 ◽  
Vol 38 (2) ◽  
pp. 231-233 ◽  
Author(s):  
H. A. Azab ◽  
Ahmed Hassan ◽  
Z. A. Khafagy
Keyword(s):  
Organic Solvent ◽  
Dissociation Constant ◽  
Potentiometric Determination ◽  
Solvent Mixtures ◽  
Second Stage

Chromatographic and Surfactant Based Potentiometric Determination of Aqueous Dissociation Constant of Mupirocin

2020 ◽  
Vol 16 (2) ◽  
pp. 158-165 ◽  
Author(s):  
Natalija Nakov ◽  
Katerina Brezovska ◽  
Vasil Karchev ◽  
Jelena Acevska ◽  
Aneta Dimitrovska
Keyword(s):  
Linear Relationship ◽  
Dissociation Constant ◽  
Spectrophotometric Method ◽  
Tween 80 ◽  
Potentiometric Determination ◽  
Chromatography Method ◽  
Pka Values ◽  
Pka Value ◽  
Aqueous Pka

Background: The available data concerning aqueous dissociation constant of mupirocin (sparingly soluble drug) are scarce. In this study, chromatographic, surfactant based potentiometric concept and spectrophotometric method were used for determination of the aqueous pKa value of mupirocin. Methods: Different approaches were used for estimation of the aqueous pKa value from the apparent pKa values obtained at four ACN concentrations, ranging from 22% to 30%. The potentiometric determination of the pKa value of mupirocin was performed using different concentration of Tween 80 as a surfactant. Results: The aqueous pKa value of mupirocin, determined for the first time by reverse-phase liquid chromatography method, was found to be 4.76. The obtained value was confirmed by potentiometric method (4.85). It was found that Tween 80 increases the pKa values. The linear relationship between the apparent pKa values and the surfactant concentrations was used as an approach for estimation of the aqueous pKa value. Both methods gave similar values for aqueous pKa which correspond with the theoretically obtained pKa value (4.88) using Pallas computer program. It was found that mupirocin gives pH-indipendent spectra, thus spectrophotometric method is not applicable for determination of pKa of this compound. Conclusion: This comprehensive approach used for the pKa determination enable us to obtained reliable results for the aqueous pKa value of mupirocin. The linear relationship between the pKa values and the nonionic surfactant concentrations could be used as a reliable and simple approach for determination of aqueous pKa value of sparingly soluble drugs.

Medium effect on the second-stage dissociation constant of N-(2-acetamido)imino diacetic acid (H2ADA)

1992 ◽  
Vol 70 (6) ◽  
pp. 1684-1687 ◽  
Author(s):  
Ahmed Hassan ◽  
H. A. Azab ◽  
S. A. El Gyar ◽  
Z. A. Khafagy
Keyword(s):  
Dissociation Constant ◽  
Aqueous Media ◽  
Acid Dissociation ◽  
Medium Effect ◽  
Solvent Mixtures ◽  
Diacetic Acid ◽  
Imino Group ◽  
Second Stage ◽  
Dissociation Equilibrium ◽  
Imino Diacetic Acid

The second-stage dissociation constant values of N-(2-acetamido)imino diacetic acid (H2ADA) were determined at 25 ± 0.1 °C by potentiometric titration in different mixed-solvent mixtures (methanol, ethanol, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, and dioxane). It was observed that the pKa value is slightly influenced as the solvent is enriched in methanol and ethanol, and remains practically constant in the presence of different amounts of DMF and DMSO. A prounounced change in the pKa value was observed as the solvent is enriched in acetone or dioxane. These results are discussed in terms of various solvent characteristics. It is concluded that the electrostatic effect has only a relatively small influence on the dissociation equilibrium of the imino group [Formula: see text]. Other solvent effects such as solvent basicity, different stabilization of the free base of the conjugate acid by hydrogen bonding interactions in aquoorganic solvent media relative to pure aqueous media, as well as proton–solvent interaction play an important role in the acid dissociation equilibrium.

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