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Two UV spectrophotometric methods have been developed, based on first derivative spectrophotometry for simultaneous estimation of doxylamine succinate, pyridoxine hydrochloride, and folic acid in tablet formulations. In method I, the concentrations of these drugs were determined by using linear regression equation. Method II is also based on first derivative spectrophotometry however simultaneous equations (Vierdot's method) were derived on derivative spectra. The first derivative amplitudes at 270.0, 332.8 and 309.2 nm were utilized for simultaneous estimation of these drugs respectively by both methods. In both the methods, linearity was obtained in the concentration range 2.5-50 μg/ml, 1-40 μg/ml and 1-30 μg/ml for doxylamine succinate, pyridoxine hydrochloride, and folic acid respectively. The developed methods show best results in terms of linearity, accuracy, precision, LOD, LOQ and ruggedness for standard laboratory mixtures of pure drugs and marketed formulations. The common excipients and additives did not interfere in their determinations.

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A highly sensitive differential pulse polarographic method has been developed for the estimation of tegaserod maleate after treating it with hydrogen peroxide solution. The oxidation of tegaserod maleate is a reversible process as the oxidized product could be reduced at hanging mercury drop electrode in a quantitative manner using differential pulse polarography mode. The limit of quantification was 0.1ng/ml. The voltametric peak was obtained at -1.05 volts in presence of 0.1M potassium chloride as supporting electrolyte. The technique could be used successfully to analyze tegaserod maleate in its tablet formulation.

A new plastic membrane ion-selective electrode for determination of metformin hydrochloride has been prepared, after forming the ion pair of metformin hydrochloride with sodium tetraphenylborate. Dioctyl phthalate and sodium tetraphenylborate were used as plasticizer and counter ion respectively. The electrode exhibited a linear potential response in the concentration range 1 × 10 -5 M-1 × 10 -1 M with slope of 42.0±0.82 mv per decade. The electrode has a rapid response time (45 s), shorter conditioning time (2 h) and a lower limit of detection (1 × 10 -5 M). The electrode showed high selectivity for metformin hydrochloride with respect to some common ions, excipients and other drugs present as combined dosage formulations. Stability studies of ion-selective membrane were carried out by differential scanning calorimetry. The electrode can successfully be applied for the analysis of metformin hydrochloride in pure solution, pharmaceutical preparations, biological fluid and in presence of its degraded products.