Reversed-phase high performance liquid chromatographic method for the determination of lansoprazole, omeprazole and pantoprazole sodium sesquihydrate in presence of their Acid-induced degradation products

A simple sensitive, selective and accurate reversed-phase high performance liquid chromatographic method was developed and validated for the quantitative determination of lansoprazole, omeprazole and pantoprazole sodium sesquishydrate in the presence of their acid-induced degradation products. The three compounds were monitored at 280 nm using Nova-Pak C(18) column and a mobile phase consisting of 0.05 M potassium dihydrogen phosphate : methanol : acetonitrile (5 : 3 : 2 v/v/v). Linearity ranges were 2-20 mug ml(-1), 2-36 mug ml(-1) and 0.5-20 mug ml(-1) for lansoprazole, omeprazole and pantoprazole, respectively. The corresponding recoveries were 100.61+/-0.84%, 100.50+/-0.80% and 99.78+/-0.88%. The minimum detection limits were 0.55, 0.54 and 0.03 mug ml(-1) for lansoprazole, omeprazole and pantoprazole, respectively. The method could be successfully applied to the determination of pure, laboratory prepared mixtures and pharmaceutical dosage forms. The results obtained were compared with the reported methods for lansoprazole and pantoprazole or the official U.S.P method for omeprazole.     

Stability indicating methods for determination of Donepezil Hydrochloride according to ICH guidelines

Stability indicating assays for determination of Donepezil Hydrochloride in presence of its oxidative degradate were developed and validated. The first three are spectrophotometric methods depending on using zero order (D(0)), first order (D(1)) and second order (D(2)) spectra. The absorbance was measured at 315 nm for (D(0)) while the amplitude was measured at 332.1nm for (D(1)) and 340 nm for (D(2)) using deionized water as a solvent. Donepezil Hydrochloride (I) can be determined in the presence of up to 70% of its oxidative degradate (II) using (D(0)), 80% using (D(1)) and 90% using (D(2)). The linearity range was found to be 8-56 microg ml(-1) for (D(0)), (D(1)) and (D(2)). These methods were applied for the analysis of I in both powder and tablet form. Also, a spectrofluorimetric method depending on measuring the native fluorescence of I in deionized water using lambda excitation 226 nm and lambda emission 391 nm is suggested. The linearity range was found to be 0.32-3.20 microg ml(-1) using this method, I was determined in the presence of up to 90% of II. The proposed method was applied for the analysis of I in tablet form as well as in human plasma. The last method depends on using TLC separation of I from its oxidative degradate II and I was then determined spectrodensitometrically. The mobile phase was methanol : chloroform : 25% ammonia (16 : 64 : 0.1 by volume). The linearity range was found to be 2-15 microg/spot. This method was applied to the analysis of I in both powder and tablet form using acetonitrile as a solvent.     

Semiconductor–superconductor phase transition of the compound LaO0.89F0.11FeSb

We report the synthesis and superconductivity in iron-based oxypnictide LaO_0.89F_0.11FeSb, with the phase transition in the resistivity at 78.6 K and the onset transition temperature at 20.3 K. This compound showed an anomalous change in the resistivity slope, where a transition between the semiconducting and superconducting state has occurred.     

The Sun and Jupiter as a binary system

I view the solar system in my paper as basically a double star, with the sun and Jupiter as components. Although the acceptance of this model may still be a philosophical choice, I introduce in my paper powerful arguments in favor of its support. Those arguments cover a wide range of conceptual, physical, and mathematical analysis.     

The influence of some organic complexing agents on the potential of copper(II) - selective electrodes. application of the silicone rubber-based electrode to the determination of citrate ion and 8-hydroxyquinoline

The behaviour of the silicone rubber-based copper(II)-selective electrode in the presence of complexing agents is discussed. The electrode shows well defined responses to several complexing agents in solutions practically free of copper(II) ions. Titrimetric determinations of citrates and 8-hydroxyquinoline with potentiometric end-point detection are described.     

Kinetic salt effects in the acid hydrolysis of potassium ethyl malonate in water and in 50% dioxane—Water mixture

The rates of the acid hydrolysis of potassium ethyl malonate in presence of KCl, NaCl, Li₂SO₄ and MgSO₄ in water and in 50% by weight of dioxane—water mixture were measured. The concentration of the added salts covered the range 0–1M. A negative salt effect on the rate of the half-ester hydrolysis was observed. The applicability ofBrønsted's equation was tested and deviations found were explained as due among other reasons, to the operation of an iondipole type of interaction. The correlation between the hydration numbers as well as the radii of the cations of the added electrolytes and the reaction rate were discussed. The activation energy was found to increase with an increase of the concentration of electrolyte due to the relative changes in solvation of the transition state as a result of hydration of the electrolytes added. The thermodynamic properties of the activated complex were calculated and discussed as functions of the salt concentration. A remarkable linear compensation between H and S was found.

---

Der kinetische Salz-Effekt bei der sauren Hydrolyse von Kaliumethylmalonat in Wasser und in 50% Dioxan—Wasser

Zusammenfassung Es wurde die Kinetik der Hydrolyse von Kaliumethylmalonat in Gegenwart von KCl, NaCl, Li₂SO₄ und MgSO₄ (jeweils 0–1M) in Wasser und in 50% (w/w) Dioxan—Wasser untersucht. Es wurde ein negativer Salz-Effekt bezüglich der Hydrolysegeschwindigkeit des Halbesters beobachtet. Es werden sowohl Korrelationen zwischen Hydratationszahlen bzw. Ionenradien und der Reaktionsgeschwindigkeit, als auch zwischen Aktivierungsenergie und Elektrolytkonzentration diskutiert. Die thermodynamischen Parameter werden als Funktion der Salzkonzentration untersucht.