Simple and rapid methods for the analysis of Sulfonamide bacteriostatic antibiotic in dosage forms

Two novel simple, precise and rapid spectrophotometric methods (Mehod A and Mehod B) are proposed for the determination of sulfamethaxazole (SFZ) using ferric chloride and potassium ferricyaide, sodium nitrite and resorcinol, as reagents. Method A is based reduction of Fe+3 by SFZ and Fe+2 produced forms complex with potassium ferricyanide to form a green colored chromogen having maximum absorption at 720nm. Method B is based on the diazotization of the drug by sodium nitrite in acidic medium at 5°C followed by coupling with resorcinol to form yellow colored species (λmax 430nm). Beer’s law is obeyed in the ranges, 4-20 and 2-10 μg/mL for method A and method B, respectively. The apparent molar absorptivities are calculated to be 0.61 x 104 and 1.089 × 104L mol-1cm-1 for method A and method B, respectively, and the corresponding Sandell sensitivity values are 0.04 and 0.023 ìg cm-2. The methods were successfully applied to the assay of SFZ in pharmaceutical formulations with satisfactory results.