Simultaneous determination of norfloxacin and tinidazole binary mixture by difference spectroscopy

A simple and rapid difference spectroscopic method was developed for the simultaneous determination of binary mixture of norfloxacin (NF) and tinidazole (TZ) without prior separation. The proposed method depends upon measuring the absorbance of NF at 291.6 nm which is the zero crossing point on the difference spectra of TZ in 0.1 N NaOH vs. 0.1 N HCl. Similarly, the absorbance of TZ was measured at 344.4 nm which is the zero crossing point on the difference spectra of NF. Beer's law was obeyed in the concentration range of 2-20 and 5-50 μg/mL for NF and TZ, respectively. The lower limits of detection (LOD) of NF and TZ are 0.23 and 0.36 μg/mL, respectively, while the lower limits of quantification (LOQ) of NF and TZ were 0.70 and 1.08 μg/mL, respectively. The precision of the method was satisfactory; the maximum value of relative standard deviations did not exceed 1.5% (n=10). The accuracy, expressed as recovery is between 98.25 and 101.8% with relative error of 0.29 and 0.23 for NF and TZ, respectively. The proposed method was successfully applied for the determination of both drugs in bulk powder, laboratory prepared mixture and commercial dosage forms such as tablets without interference from the commonly encountered excipients and additives. The results obtained are in good agreement with those obtained by the reference methods.