Optical Spectral Analysis of 4-Aminobenzenesulfonamide through Azo Coupling Reaction and its Commercial Chemical Applications

Determination of 4-aminobenzenesulfonamide (SFA) by azo-coupling with quercetin, producing a dark yellow color. The method is based on an azo-coupling reaction between SFA and quercetin. The SFA is first diazotized using hydrochloric acid and sodium nitrite at 0–5 °C, then coupled in an alkaline medium. The resulting dark yellow, water-soluble product exhibits a maximum absorbance at 413 nm. The experimental conditions were initially optimized using a univariate approach (OVAT) by examining the effects of individual variables. For further improvement, a central composite design was used to characterize system behavior and identify optimal conditions across multiple variables. The method demonstrated good linearity, with Beer’s law obeyed over the concentration range of 1–10 μg.mL-1. The detection limit was 1.12 μg.mL-1. The molar absorptivity and Sandell’s sensitivity were 2.53×10⁴ L.mol⁻¹.cm⁻¹ and 6.82×10⁻³ μg.cm-2, respectively. The resulting color remained stable for more than one hour. The proposed method was successfully applied to sulfadiazine pharmaceutical formulations