Protolitičke ravnoteže u homogenom i heterogenom sistemu ketokonazola i njegovo direktno spektrofotometrijsko određivanje u tabletama

The acid-base equilibria of a diprotic, slightly hydrosoluble base ketoconazole were studied in homogeneous and heterogeneous water systems. The determinations were performed at 25ºC at a constant ionic strength of M(NaCl). The acidity constant Ka1 was determined by potentiometric (pKa1 3.20) and spectrophotometric (pKa1 3.26) methods. A pKa2 constant of 6.10 was obtained based on the equilibrium constants pKs0 4.84 and pKs1 -1.26, determined in a heterogeneous ketoconazole system. The obtained values of the constants served to calculate the solubility and the distribution of the equilibrium forms of ketoconazole as a function of pH. On the basis of the distribution of the equilibrium forms of ketoconazole, a spectrophotometric method for the determination of its content in commercial tablets was developed. The determinations were performed at 225 nm in 0.1 M HCl. The method is simple and rapid and enables the direct spectrophotometric determination of the content of ketoconazole without previous isolation.Proučene su kiselinsko-bazne ravnoteže u homogenom i heterogenom vodenom sistemu ketokonazola, diprotične teško rastvorne baze. Određivanja su vršena na temperaturi 25ºC i pri konstantnoj jonskoj sili 0,1M(NaCl). Kiselinska konstantaKa1 određena je potenciometrijski (pKa1 3,20) i spektrofotometrijski (pKa1 3,26). Konstanta pKa2 6,10 izračunata je iz ravnotežnih konstanti određenih u heterogenom sistemu: pKs0 4,84 i pKs1 -1,26. Na osnovu dobijenih vrednosti za konstante izračunata je rastvorljivost i raspodela ravnotežnih oblika ketokonazola u funkciji pH. Na bazi raspodele ravnotežnih oblika ketokonazola predložena je spektrofotometrijska metoda za njegovo određivanje u komercijalnim tabletama. Određivanja su vršena na talasnoj dužini 225 nm u 0,1M HCl.Metoda je jednostavna i brza, i omogućava direktno spektrofotometrijsko određivanje ketokonazola, bez prethodnog izolovanja

Protolytic equilibria in homogeneous and heterogeneous systems of ketoconazole and its direct spectrophotometric determination in tablets

The acid-base equilibria of a diprotic, slightly hydrosoluble base ketoconazole were studied in homogeneous and heterogeneous water systems. The determinations were performed at 25 ºC at a constant ionic strength of 0.1M(NaCl). The acidity constant Ka1 was determined by potentiometric (pKa1 3.20) and spectrophotometric (pKa1 3.26) methods. A pKa2 constant of 6.10 was obtained based on the equilibrium constants pKs0 4.84 and pKs1 1.26, determined in a heterogeneous ketoconazole system. The obtained values of the constants served to calculate the solubility and the distribution of the equilibrium forms of ketoconazole as a function of pH. On the basis of the distribution of the equilibrium forms of ketoconazole, a spectrophotometric method for the determination of its content in commercial tablets was developed. The determinations were performed at 225 nm in 0.1 M HCl. The method is simple and rapid and enables the direct spectrophotometric determination of the content of ketoconazole without previous isolation

The point of zero charge and sorption of cadmium (II) and strontium (II) ions on synthetic hydroxyapatite

Surface properties of synthetic well-crystallized hydroxyapatite were investigated. Points of zero charge (pH(PZC)) for different solid to solution ratios were determined by the batch equilibration technique, using KNO3 as a background electrolyte. It has been found that the decrease in solid to solution ratio from 1:100 to 1:500 leads to a decrease in pH(PZC) from 6.1 to 4.1, respectively. Sorption of Cd2+ ions is not influenced by the initial pH value in the investigated range (5-7), while sorption of Sr2+ -ions, determined in the wider pH range (4.5-11.5), depends only on the initial pH higher than 10, i.e. final pH values higher than 4.5. Negative surface charge established when pH of the solution is higher than pH,, leads to a more effective cation sorption. (C) 2000 Elsevier Science B.V. All rights reserved

A Contribution to the Glimepiride Dissociation Constant Determination

Knowledge of druglike properties, such as dissociation constants (pK(a)), is of great importance in drug development and analysis. However, poor aqueous Solubility often Causes serious limitations ill accurate determination of a drug's pK(a). In this Study, the apparent dissociation constant (pK(a)') of the poorly soluble drug, glimepiride, has been determined by application of the spectrophotometric and Solubility methods. Compared to the literature reported glimepiride pK(a)' values of 4.99 +/- 0.50 and 6.2 +/- 0.1, the values obtained in the present study were 8.07 +/- 0.02 and 7.26 +/- 0.01 determined by the spectrophotometric and Solubility method, respectively. In addition, the advantages of these two methods in pK(a)' determination of glimepiride are discussed