Dual-mode gradient HPLC and TLC densitometry methods for the simultaneous determination of paracetamol and methionine in the presence of paracetamol impurities

Ibrahim, Hany; Hamdy, Abdallah M; Merey, Hanan A; Saad, Ahmed S

BACKGROUND: Paracetamol is one of the most widely analgesic and antipyretic drugs recently integrated into the supportive therapy of COVID-19. The pharmaceuticals containing methionine with paracetamol may contribute to avoid hepatotoxicity and eventual paracetamol overdose-dependent death. OBJECTIVE: The current work purposes to develop and validate two chromatographic methods for the simultaneous determination of methionine and paracetamol in presence of two paracetamol impurities (4-nitrophenol and 4-aminophenol). METHODS: Two chromatographic methods were established and validated according to the International Conference on Harmonization guidelines. The first one was a 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 paracetamol in its pure form or in pharmaceutical formulations with methionine in quality control laboratories. CONCLUSIONS: The corresponding methods are suitable to determine methionine and paracetamol in the presence of paracetamol impurities. HIGHLIGHTS: The study achieves the analysis of methionine and paracetamol in the presence of paracetamol impurities via the application of HPLC and TLC- densitometry methods.