The development of spectrophotometric and electroanalytical methods for ascorbic acid and acetaminophen and their applications in the analysis of effervescent dosage forms

The electroanalytical study of ascorbic acid, acetaminophen and of several mixtures of these compounds in different ratios has been made by using a ca rbon paste electrode (CPE-graphite:solid paraffin 2:1) as working electrode and an Ag/AgCl reference electrode. The potential curves were recorded usi ng different concentrations of ascorbic acid and acetaminophen by measuring samples between 10 and 50 mu l. The oxidation reactions were studied in a potential range from -0.1 to + 1.3 V with different sweep rates, at differe nt current sensitivities, in stationary working conditions and stirring bef ore each replicate. The oxidation of ascorbic acid occurs at + 0.31 +/- 0.0 2 V and the oxidation of acetaminophen at + 0.60 +/- 0.05 V: meanwhile, the current has a linear variation for the following concentration ranges: 10( -3)-10(-2) M for the ascorbic acid and 3 x 10(-6)-7.5 x 10(-3) M for acetam inophen (r(2) = 0.999 for both ascorbic acid and acetaminophen). The mixtur es of ascorbic acid and acetaminophen were made as follows: 1:1, 1:2, 1:3, 2:1, and 3:1. The studies revealed the alteration of the voltammograms proc essed according to the validation methodology. The best potential variation range for different current sensitivities, the influence of the sweep rate , of the solvent volume and of the pH were studied. The mutual interference s of the compounds in the mixtures and the electroactive compounds in the p harmaceutical dosage forms, especially effervescent ones, also made the obj ect of the research. The same mixtures were studied using the direct spectr ophotometric method that revealed a lot of spectral interferences. In order to solve this problem, an appropriate separation or an indirect spectropho tometric method (the apparent content curves method) were used. The spectro photometric and voltammetric methods developed were used to determine ascor bic acid and acetaminophen in different dosage forms (vials, tablets, suppo sitories and effervescent dosage forms). The results were compared with tho se obtained by other techniques. (C) 2000 Elsevier Science B.V. All rights reserved.