Titrimetric and spectrophotometric assay of some antihistamines through the determination of the chloride of their hydrochlorides.

Two simple, rapid and reliable methods for the determination of four antihistamines based on the measurement of the chloride of their hydrochlorides are described. In the titrimetric method, the chloride content of each drug is determined by titrating with mercury(II) nitrate using diphenylcarbazone-bromothymol blue as indicator. In the spectrophotometric method, to a fixed concentration of mercury(II)-diphenylcarbazone complex different amounts of drug are added and the decrease in absorbance of mercury(II)-diphenylcarbazone complex, consequent to the replacement of diphenylcarbazone of the complex by the chloride of the drug, was measured at 540 nm. The stoichiometry of the reaction that forms the basis for titrimetry is assessed. Different variables affecting the color formation in spectrophotometry were studied and optimized. At the wavelength of maximum absorption, Beer's law is obeyed in the 0-100 microg ml(-1) range. The molar absorptivity and Sandell sensitivity are calculated. The proposed methods were applied for the analysis of pharmaceutical formulations containing these drugs. Statistical treatment of the experimental results indicates that the procedures are precise and accurate. Excipients used as additives in pharmaceutical formulations did not interfere in the proposed procedures as shown by the recovery studies.