RP-HPLC-DAD method development and validation of L-lysine hydrochloride: application to bulk drug substance and multivitamin oral suspension

L-lysine is an essential amino acid that contains a hydrophobic chain and fewer chromophore groups. Various L-lysine-based products are currently available in the market, and various analytical methods are reported in the literature; but their implementation to analyze L-lysine based products is highly cost-effective and requires considerable efforts to prepare the sample/derivatization. Currently, the developed method is being used to quantify L-lysine hydrochloride in the multivitamin oral suspension production in the pharmaceutical industry. Therefore, the aim of the work was to develop a novel, simple, sensitive, accurate, cost-effective, precise, and robust RP-HPLC-DAD method to quantify L-lysine hydrochloride in bulk drug substances and multivitamin oral suspension using C8 column, which may give more efficiency for amino acid analysis without any derivatization. Optimized mobile phase composition consists of solvent A (phosphate buffer: acetonitrile 95:5 v/v) and solvent B (Phosphate buffer: acetonitrile 5:95 v/v). Buffer pH was adjusted to 2.50 with 3 mol L⁻¹ Orthophosphoric acid. 1-Heptane sulphonic acid anhydrous sodium salt was used as an ion-pairing reagent in the buffer. The detector's wavelength was set at 208 nm with a mobile phase flow rate of 1 mL/minute. Limit of detection (\({L}_{\mathrm{D}}\)) and limit of quantification (\({L}_{\mathrm{Q}}\)) were found to be 17.80 g/mL and 53.94 g/mL, respectively. Excellent recovery was observed in the accuracy analysis of the sample L-lysine hydrochloride. The advantages of this newly developed method are very specific and cost-effective and do not require sample preparation and sample pretreatment. This analysis can be performed with an available C8 column and HPLC–UV detector that proves the cost-effectiveness of the developed method than the currently available analytical methods for the analysis of L-lysine based products.