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The density (q), viscosity (g) and ultrasonic speed (U) of the pure solvents: 1,4-dioxane (DO), ethyl acetate (EA), tetrahydrofuran (THF) and solutions of the biologically active 1,1 0 -bis(3-methyl-4-ethoxyacetylphenoxy)cyclohexane were investigated at four temperatures: 298, 303, 308 and 313 K over a wide range of concentrations (0.1-0.01 molÁdm -3 ) to understand molecular interactions in these solutions. Various acoustical and thermodynamic parameters such as specific acoustical impedance (Z), isentropic (adiabatic) compressibility (j S ), Rao's molar sound function (R m ), van der Waals constant (b), internal pressure (p), free volume (V f ), intermolecular free path length (L f ), classical absorption coefficient {(a/f 2 ) Cl }, viscous relaxation time (s), Gibbs energy of activation (DG*), enthalpy of activation (DH*) and entropy of activation (DS*) were determined using the q, g and U data. A good to excellent correlation between a given parameter and concentration (C) is observed at all temperatures (T) and solvent systems studied. A linear increase or decrease of acoustical and thermodynamic parameters with concentration and temperature indicate the presence of strong molecular interactions in the solutions. DG* decreases linearly with increasing concentration and temperature in the DO system, while it decreases with C and increases with temperature in the EA and THF systems. The enthalpy of activation (DH*) was found to be practically independent of concentration but DH* and DS* were found to be slightly concentration dependent. In the DO system they are positive, while in the EA and THF systems they are negative.

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Density (ρ), viscosity (η), ultrasonic speed (U), and thermo-acoustical parameters such as specific acoustical impedance (Z), adiabatic compressibility ( a ), internal pressure (π), free volume (V f ), inter molecular free path length (L f ), Van der Waals constant (b), viscous relaxation time (), classical absorption coefficient (α/f 2 ) cl , Rao's molar sound function (R m ), solvation number (S n ), Gibbs free energy of activation (ΔG*), enthalpy of activation (ΔH*) and entropy of activation (ΔS*) of biologically active 1,1'-bis(3-methyl-4-carboxyethylphenoxy)cyclohexane (BMCPC) in 1,4-dioxane (DO), ethyl acetate (EA), tetrahydrofuran (THF) have been studied at four different temperatures: 298, 303, 308 and 313 K to understand the molecular interactions in the solutions. A good to excellent correlation between a given parameter and concentration is observed at all temperatures and solvent systems studied. Linear increase or decrease [except (α/f 2 ) cl ] of acoustical parameters with concentration and temperature indicated the existence of strong molecular interactions. ΔG* decreased linearly with increasing concentration and temperature in DO and EA systems and increased with temperature in THF system. ΔH* and ΔS* are found practically concentration independent in case of DO and EA system but both are found concentration dependent in THF system

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Objective: A simple, sensitive, and accurate in-vitro dissolution method has been developed for Olmesartan Medoxomil (OLM), Chlorthalidone (CHLR) & Cilnidipine (CIL) drug combination according to USP dissolution testing methodologies with different discriminating mediums and validated as per ICH guidelines. Methods: The in-vitro dissolution profile was obtained using 900 ml of phosphate buffer pH 6.8 with 1.0% SLS at 37 °C ± 0.5 °C as dissolution medium and USP II (paddle) at 75 rpm. The average % in-vitro drug release was above 80% within 45 minutes for the above drug combination. The drug release profile was evaluated by RP-HPLC method. Chromatographic separation was done on Hypersil-BDS C-18 (12.5cm x 4.6mm x 5µm) column using gradient program with initial mobile phase ratio of 55:45 (v/v) mixture of ammonium acetate buffer (pH 5.0) and acetonitrile at a flow rate of 1.0 ml/min with detection wavelength 260 nm. Results: The method was validated with respect to specificity, linearity, precision, accuracy, and robustness. The method was found to be linear in the range of 7.0-21.0 μg/ml for CHLR (R2 = 0.9982), 22.5-67.5 μg/ml for OLM (R2 = 0.9999) and 5.5 -16.5 μg/ml for CIL (R2 = 0.9995) respectively. The % recovery data were found between 98.3 % to 104.1%. The % RSD for method and intermediate precision of method did not exceed more than 2%. Conclusion: The proposed in-vitro method can be applied successfully for routine quality control analysis to check the quality of above drug combination.