Ratio subtraction and isosbestic point methods are 2 innovating spectrophotometric methods used to determine vincamine in the presence of its acid degradation product and a mixture of cinnarizine (CN) and nicergoline (NIC). Linear correlations were obtained in the concentration range from 840 g/mL for vincamine (I), 622 g/mL for CN (II), and 636 g/mL for NIC (III), with mean accuracies 99.72 0.917 for I, 99.91 0.703 for II, and 99.58 0.847 and 99.83 1.039 for III. The ratio subtraction method was utilized for the analysis of laboratory-prepared mixtures containing different ratios of vincamine and its degradation product, and it was valid in the presence of up to 80 degradation product. CN and NIC in synthetic mixtures were analyzed by the 2 proposed methods with the total content of the mixture determined at their respective isosbestic points of 270.2 and 235.8 nm, and the content of CN was determined by the ratio subtraction method. The proposed method was validated and found to be suitable as a stability-indicating assay method for vincamine in pharmaceutical formulations. The standard addition technique was applied to validate the results and to ensure the specificity of the proposed methods.
A high performance liquid chromatographic method was developed and validated for determination of meclophenoxate hydrochloride (I) in the presence of its degradation product (p-chlorophenoxy acetic acid) (II). Separation of (I) from (II) was performed using a ZORBAX ODS column with a mobile phase consisting of 0.2% triethylamine in 0.01 M ammonium carbonate: acetonitrile (70:30 v/v). The method showed high sensitivity with good linearity over the concentration range of 50 to 400 mg/ml. The method was successfully applied to the analysis of a pharmaceutical formulation containing (I) with excellent recovery. A kinetics investigation of the alkaline hydrolysis of (I) was carried out in sodium hydroxide solutions of 1, 1.5 and 2 N by monitoring the parent compound itself. The reaction order of (I) followed pseudo-ˆrst order kinetics. The activation energy could be estimated from the Arrhenius plot and it was found to be 12.331 kcal/mole.
The construction and electrochemical response characteristics of polyvinyl chloride (PVC) membrane sensors for the determination of meclophenoxate hydrochloride (I) and pyritinol dihydrochloride (II) in presence of their degradation products are described. The sensors are based on the use of the ion-association complexes of (I) and (II) cation with sodium tetraphenyl borate and ammonium reineckate counteranions as ion-exchange sites in the PVC matrix. In addition b-cyclodextrin (b-CD) membranes were used in the determination of I and II. These ion pairs and b-CD were then incorporated as electroactive species with ortho nitrophenyl octyl ether (oNPOE) as a plasticizer. Three PVC sensors were fabricated for each drug, i.e. meclophenoxate tetraphenyl borate (meclo-TPB), meclophenoxate reineckate (meclo-RNC) and meclophenoxate b-cyclodextrin (meclo-b-CD), and the same was done for pyritinol (pyrit-TPB), (pyrit-RNC) and (pyrit-b-CD). They showed near Nernestian responses for meclophenoxate over the concentration range 10 -5 -10 -2 with slopes of 52.73, 51.64 and 54.05 per concentration decade with average recoveries of 99.92± 1.077, 99.96±0.502 and 100.03±0.763 for meclo-TPB, meclo-RNC and meclo-b-CD respectively. Pyritinol also showed near Nernestian responses over the concentration range of 3.162×10 -6 -3.162×10 -4 for pyrit-TPB and pyrit-RNC, and 10 -6 -3.162×10 -4 for pyrit-b-CD with slopes of 30.60, 31.10 and 32.89 per concentration decade and average recoveries of 99.99±0.827, 100.00±0.775 and 99.99±0.680 for pyrit-TPB, pyrit-RNC and pyrit-b-CD respectively. The sensors were used successfully for the determination of I and II in laboratory prepared mixtures with their degradation products, in pharmaceutical dosage forms and in plasma.
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