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 ± 2 °C). 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.