Spectrophotometric Determination of Chloramphenicol in Pharmaceutical Formulations by Diazotization and Coupling Reaction

Chloramphenicol (CAP), a broad-spectrum antibiotic, was quantitatively analyzed in various pharmaceutical formulations using a rapid and sensitive spectrophotometric method, with the characterization via Fourier-transform infrared (FTIR) spectroscopy. The reduction of CAP was achieved using zinc powder in the presence of concentrated hydrochloric acid, followed by diazotization with sodium nitrite (NaNO₂). The resulting diazonium salt was subsequently coupled with three distinct chromogenic reagents cresol, resorcinol, and 2-naphthol—yielding yellow, and red azo dyes, respectively. Maximum absorbance for the dye complexes was observed at wavelengths of 420 nm (cresol), 440 nm (resorcinol), and 540 nm (2-naphthol). The method exhibited linearity within the concentration ranges of 3.8–30 µg/mL for cresol, 0.9–10 µg/mL for resorcinol, and 3.7–25 µg/mL for 2-naphthol, in accordance with Beer’s law. Molar absorptivity and Sandell’s sensitivity were recorded as follows: 2.9 × 10³ L.mol⁻¹·cm⁻¹ and 0.112 µg.cm⁻² (cresol), 3.4×104 L.mol⁻¹·cm⁻¹ and 0.0094 µg.cm⁻² (resorcinol), and 1.4×10³ L.mol⁻¹·cm⁻¹ and 0.23 µg.cm⁻² (2-naphthol), indicating high sensitivity of the developed method. Precision analysis revealed that the 2-naphthol reagent provided the most accurate results with a coefficient of variation ranging from 0.81% to 2.59%, followed by resorcinol, while the cresol-based method demonstrated comparatively lower precision. This spectrophotometric technique was successfully applied for the determination of CAP in commercial pharmaceutical formulations, including 0.5% eye drops and 1% eye ointments.