Simultaneous determination of norfloxacin and sulfadiazine by first-derivative spectrophotometry

Norfloxacin (nf) and sulfadiazine (sdz) are antibacterial agents of synthetic origin. nf is a second-generation fluoroquinolone clinically successful to treat urinary tract infections, which exhibits rapid bactericidal action, broad-spectrum efficacy, good tissue penetration, acceptable bioavailability, and tolerable adverse effects. sdz is a systemic antibacterial sulfonamide used for the treatment of urinary and genitourinary tract infections, burns, sinusitis, and meningococcal meningitis. in the present study, we set up and validated a spectrophotometric technique because of the need to determine and quantify both substances simultaneously. since zero-order uv absorption spectra of both drugs overlap in the region between 240 and 290 nm, we selected the first-order derivative strategy, measured as zero-crossing. this technique has the advantage of being simple, low-cost, and fast. the guidelines of the international conference on harmonization were followed. nf was determined at a λmax of 257 nm, and it showed linearity in the range 3.2 10^-6 – 3.2 10^-5, whereas sdz was determined at a λmax of 272 nm, and it showed linearity in the range of 3.0 10^-6 – 3.0 10^-5. in both cases, the correlation coefficient was 0.999. the methodology was statistically validated by evaluating the following parameters: limit of detection and quantification, precision (repeatability and intermediate precision), specificity, and accuracy. the results obtained indicate that the methodology proposed is suitable for the simultaneous determination of nf and sdz in solution.