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An spectrophotometric UV-visible technique used to quantify diclofenac and its application to pharmaceutical preparations is described, based on diclofenac oxidation by Fe(III) in the presence of ophenanthroline. The formation of tris (o-phenanthroline)-Fe(II) complex (ferroin) upon diclofenac reaction was investigated. Absorbance of ferroin complex was measured at 506 nm. This method was tested on 50 mg tablets. Operating with placebos, it was found that excipients do not interfere with the determination. A good linearity was found [y = (0.0294 ± 0.0041)x + (0.1326 ± 0.0559)] with r2 = 0.9982, calibration curve showed a linear range from 5-15 μg/mL of diclofenac. The proposed method was found to be highly precise, having a relative standard deviation (CV) below 2.0 % in repeatability and intermediate precision studies. Accuracy: based on the average recovery of known amounts of drug in placebo was 98.07-101.97 % values that fall within the requirements set by USP and ANMAT (98.0-102.0 %). This method was found to be simple, rapid, specific, linear, reliable and robust, allowing the determination without preliminary extraction procedures., Colegio de Farmacéuticos de la Provincia de Buenos Aires

A spectrophotometric method was developed for the analysis of metformin, based on its reaction with the biuret reagent. A complex with λmax = 495 nm and stoichiometry 2:1 (metformin-Cu) is generated wich allows the quantification of metformin in tablets. Physicochemical parameters of the product were determined. Sample conditioning by centrifugation was necessary to separate insoluble excipients. Polyvinylpyrrolidone (PVP) was isolated by a solid-liquid extraction with SPE-SCX resin in order to eliminate its interference on the absorbance of the complex. The proposed method was found to be highly precise, having a relative standard deviation, CV % = 0.68. Using this approach the calibration curve showed r2 = 0.9949 with 95 % confidence level, value included inside the limits established by USP. Accuracy based on the average recovery of known amounts of drug in placebo was in the range of 98.61 to 99.97. Results allow the application of this analytical methodology to metformin tablets., Colegio de Farmacéuticos de la Provincia de Buenos Aires

A spectrophotometric method is proposed for the analysis of atenolol, based on its reaction with the indicator phenol red in an acetone environment. Experimental conditions for the formation of an ion pair complex peaking at 388 nm were optimized. The method is linear in the range of 1 to 5 mg/mL with a correlation coefficient (n = 30) of 0.9968. Stoichiometry of the reaction is 1: 1. Free energy change (ΔG) for complex formation and stability constant (KF) have been calculated. Working with placebo it was found that excipients do not interfere in the analysis. The proposed method was applied to tablets provided by the Medicinal Plant of Corrientes (Plamecor), Argentina. Recoveries from 99.67 to 100.17 were achieved. Results were compared (F test and t test) favorably with those given by official methods. (HPLC - UV)., Colegio de Farmacéuticos de la Provincia de Buenos Aires