Dual-Mode Gradient HPLC and TLC Densitometry Methods for the Simultaneous Determination of Paracetamol and Methionine in the Presence of Paracetamol Impurities

Abstract

Abstract Background Paracetamol (PC) is one of the most widely used analgesic and antipyretic drugs and has recently been integrated into the supportive therapy of COVID-19. Pharmaceuticals containing methionine (MT) with PC may contribute to avoid hepatotoxicity and eventual PC overdose-dependent death. Objective The current work purposes to develop and validate two chromatographic methods for the simultaneous determination of MT and PC in the presence of two PC impurities (4-nitrophenol [NP] and 4-aminophenol [AP]). Method Two chromatographic methods were established and validated according to the International Conference on Harmonization guidelines. The first one was an RP-HPLC/UV method based on applying a “dual-mode” gradient elution. The separation was realized via varying both the composition of the ternary mobile phase (acetonitrile–methanol–water) and its flow rate. This strategy enabled a relatively rapid analysis with a satisfactory resolution, although the investigated compounds exhibit a significant difference in lipophilicity. The second one relied on TLC-densitometry, where the optimum separation was realized using a quaternary mobile phase system composed of butanol–dioxane–toluene–methanol (8:2.5:3.5:0.3, by volume). Both methods were monitored at 220 nm. Results The developed methods were proven to be robust, accurate, specific, and appropriate for the routine analysis of PC in its pure form or in pharmaceutical formulations with MT in quality control laboratories. Conclusions The corresponding methods are suitable to determine MT and PC in the presence of PC impurities. Highlights The study achieves the analysis of MT and PC in the presence of PC impurities via the application of HPLC and TLC-densitometry methods.