Innovative UV derivative spectrophotometric method for simultaneous quantification of sulfadimethoxine and metronidazole

This study developed and validated an analytical method based on derivative spectrophotometry for the simultaneous determination of sulfadimethoxine (SDM) and metronidazole (MTZ) in veterinary medicines, without the need for prior separation of the drugs. The method employed acetonitrile PA as the solvent at room temperature (25 ± 2ºC). MTZ was quantified using zero-order spectrophotometry at 320 nm, while SDM was determined using first-order spectrum at 266 nm, applying the zero-crossing technique. Analytical validation of the developed methods demonstrated robust results, with a correlation coefficient (r) > 0.990 in the concentration range of 3.0-21.0 μg.mL -1 , satisfactory limits of detection (MTZ: 0.21 μg.mL -1 ; SDM: 0.17 μg.mL -1 ) and quantification (MTZ: 0.63 μg.mL -1 ; SDM: 0.51 μg.mL -1 ), precision (relative standard deviation (RSD) <1.9) and accuracy (recovery of 98.0-102.0%). With operational simplicity and low cost, the developed method can be adopted for the routine analysis and quality control of medicines with a fix dose combination of these two drugs. • A new derivative spectrophotometry was developed for simultaneous determination of metronidazole and sulfadimethoxine. • Metronidazole was determined by zero-order spectrophotometry at 320 nm. • Sulfadimethoxine was determined from first-order spectrum at 266 nm using zero-crossing technique. • The method was selective; no interference from pharmaceutical excipients was seen. • The method proved to be simple, cost-effective, and useful for routine quality control.