TLC vs. HPLC: A green comparison for veterinary drug analysis

This work describes two analytical methods for determining lidocaine (LD) and oxytetracycline (OTC) in veterinary dosage form: a traditional Thin-Layer Chromatography (TLC) method and a more environmentally friendly Reversed-Phase High-Performance Liquid Chromatography (RP-HPLC) method. Initially, the TLC method was used due to its speed, simplicity, and accuracy. It successfully separated LD and OTC in veterinary dosage forms with a linearity range of 0.5-11.0 mu g/band for LD and 4.0-34.0 mu g/band for OTC. However, TLC proved to be inadequate for resolving the binary mixture in the presence of toxic lidocaine impurity (2,6-dimethylaniline) (DMA), and was less environmentally friendly. Consequently, an RP-HPLC method was developed using a C18 column and a mobile phase consisting of ethanol and phosphate buffer (pH 7) in a 70:30 ratio, with a flow rate of 1.0 mL/min. This method effectively separated OTC, LD and DMA, using a PDA detector at wavelengths of 272, 232, and 210 nm and with retention times of 1.529, 2.77, and 3.581 min for OTC, DMA, and LD respectively. The RP-HPLC method showed linearity ranges of 270.0-972.0 mu g/mL for OTC, 0.5-25.0 mu g/mL for DMA, and 5.0-18.0 mu g/mL for LD. Both methods were validated for linearity, precision, accuracy, robustness, detection limit, and quantitation limit. The greenness of each method was evaluated using NEMI, Eco-scale, and Agree tools, with results demonstrating the RP-HPLC method as the more environmentally sustainable method.