Densitometric and UV-Spectrophotometric Methods for Simultaneous Determination of Spiramycin adipate in Binary Mixture with Oxytetracycline-HCl or Tetracycline-HCl

Abstract

Five methods were developed for simultaneous determination of spiramycin adipate and oxytetracycline-HCl and/or tetracycline-HCl in their pharmaceutical formulations. The first one was a densitometric evaluation of thin-layer chromatograms using a mobile phase of methanol: Butanol: Chloroform: Ammonia 1% (5:1:1:1, by volume). The plates were visualized under UV lamp at 254 nm where spots appeared at Rf 0.76, 0.30 and 0.37 for spiramycin adipate, oxytetracycline-HCl and tetracycline-HCl, respectively. The chromatograms of the drugs were measured densitometrically at 240 nm for spiramycin adipate and at 350 nm for both oxytetracycline-HCl and tetracycline-HCl in the range of 0.1-0.8 µg mL-1 and 0.1-1.0 µg mL-1, respectively. Likewise, the simultaneous estimation of the cited drugs was performed by four spectrophotometric methods. Method A was a mean centering (MC) which provided spiramycin adipate determination at 232 nm together with oxytetracycline-HCl or tetracycline-HCl, both at 282, 286, 321, 324, 345 and 364 nm. Method B was a third derivative (3D) through which spiramycin adipate could be estimated at 256 nm while the wavelength 281 nm was selected for oxytetracycline-HCl or tetracycline-HCl determination. Method C was a derivative ratio (1DR) that was established to determine spiramycin adipate only in the presence of oxytetracycline-HCl or tetracycline-HCl at 225.6 and 240 nm. Method D was an induced dual wavelength (IDW) which allowed the determination of oxytetracycline-HCl in presence of spiramycin adipate and up to 50% of its impurity tetracycline. The calibration curves were linear over the concentration range of 5-70 µg mL-1 for spiramycin adipate and 5-60 µg mL-1 for both oxytetracycline-HCl and tetracycline-HCl. The obtained results were statistically analyzed and found to be in accordance with those given by reported methods. The validity of the methods was evaluated according to ICH guidelines.