Development of an RP-HPLC Method for Quantifying Diclofenac Diethylamine, Methyl Salicylate, and Capsaicin in Pharmaceutical Formulation and Skin Samples
Lubna H. M. AlNahwa, Hazim M. Ali, Tamer H. A. Hasanin, Khaled Shalaby, Mutairah S. Alshammari, Alaa Muqbil Alsirhani, Sabrein H. Mohamed
Abstract
An RP-HPLC method with a UV detector was developed for the simultaneous quantification of diclofenac diethylamine, methyl salicylate, and capsaicin in a pharmaceutical formulation and rabbit skin samples. The separation was achieved using a Thermo Scientific ACCLAIMTM 120 C18 column (Waltham, MA, USA, 4.6 mm × 150 mm, 5 µm). The optimized elution phase consisted of deionized water adjusted to pH = 3 using phosphoric acid mixed with acetonitrile in a 35:65% (v/v) ratio with isocratic elution. The flow rate was set at 0.7 mL/min, and the detection was performed at 205 nm and 25 °C. The method exhibits good linearity for capsaicin (0.05–70.0 µg/mL), methyl salicylate (0.05–100.0 µg/mL), and diclofenac diethylamine (0.05–100.0 µg/mL), with low LOD values (0.0249, 0.0271, and 0.0038 for capsaicin, methyl salicylate, and diclofenac diethylamine, respectively). The RSD% values were below 3.0%, indicating good precision. The overall greenness score of the method was 0.61, reflecting its environmentally friendly nature. The developed RP-HPLC method was successfully applied to analyze Omni Hot Gel® pharmaceutical formulation and rabbit skin permeation samples.