Stability indicating methods for assay of mequitazine in presence of its degradate

Six procedures have been suggested for the determination of the antihistaminic agent, mequitazine, in the presence of its degradate. Mequitazine, having a phenothiazine group, undergoes peroxide oxidation and the corresponding sulphone is produced. Its identity was confirmed by IR and MS. The first procedure is based on determination of mequitazine by HPLC with UV detection at 256 nm. The mobile phase used is acetonitrile, ortho phosphoric acid (50:50) using caffeine as an internal standard. Linearity range is 1.00-9.00 microg/ml. The second determination is a densitometric procedure based on the determination of mequitazine in the presence of its degradate at 256 nm using the mobile phase, chloroform:methanol:ammonia (50:18:3). Linearity range is 1.25-7.50 microg per spot. The third procedure is spectrophotometric, where a mixture of mequitazine and its degradate are resolved by first derivative ratio spectra. Linear calibration graphs of first derivative values at wavelengths 210.2, 247 and 259.8 nm are obtained. On carrying out measurements at the three mentioned wavelengths, the linearity range is found to be 1.00-10.00 microg/ml. The fourth procedure is based on first derivative spectrophotometry, where D(1) measurements are carried out at 290 nm. Linearity range is 1.00-10.00 microg/ml. The fifth procedure is based on the reaction of mequitazine with 3-methyl-2-benzothiazolinone hydrazone (MBTH) in the presence of ferric chloride. A stable violet colored oxidative coupling product is formed, which is measured spectrophotometrically at 685 nm. The optimum experimental parameters for the reaction have been studied and assigned. Linearity range is 1.00-16.00 microg/ml. The sixth procedure is based on the reaction of mequitazine in the presence of its degradate with 2,6-dichloroquinone-4-chloroimide (Gibbs reagent) in aqueous methanolic medium. The reddish-brown colored condensation product is measured at 405 nm. The optimum experimental conditions for the reaction have been studied. Linearity range is 50.00-600.00 microg/ml. The validity of the described procedures was assessed by applying the standard addition technique. Statistical analysis of the results has been carried out revealing high accuracy and good precision. The suggested procedures could be used for the determination of mequitazine, both in pure and dosage forms, as well as in the presence of its degradate.