Validated simultaneous determination of antipyrine and benzocaine HCl in the presence of benzocaine HCl degradation product

Abstract

Two validated, sensitive and highly selective stability-indicating methods were adopted for the simultaneous quantitative determination of antipyrine (ANT) and benzocaine HCl (BEN) in the presence of the degradation product of benzocaine HCl [p-aminobenzoic acid (PABA)]. The first method was high performance liquid chromatography, where a mixture of antipyrine (ANT), benzocaine HCl (BEN) and degradation product of benzocaine HCl (PABA) is separated on a C₈ ZORBAX analytical column (5 μm, 4.6 × 150 mm I.D.) using acetonitrile–phosphate buffer of pH 5.5 (25 : 75, v/v) as the mobile phase. The drugs were detected at 270 nm over a concentration range of 10–100 μg mL⁻¹ and 5–100 μg mL⁻¹, with mean percentage recoveries of 100.22% (S.D. 1.375) and 99.77% (S.D. 1.089) for antipyrine and benzocaine HCl, respectively. The second method was thin layer chromatography combined with the densitometric determination of the separated bands at 275 nm. Adequate separation was achieved using silica gel 60 TLC F₂₅₄ plates and toluene–acetone–methanol–ammonia (8 : 3 : 3 : 0.1 by volume) as the mobile phase. The proposed methods were applied for the analysis of antipyrine and benzocaine HCl in their pharmaceutical formulation, and the results were statistically compared with the reported methods.