Colorimetric determination of artemisinin derivatives using 4-nitro-1-naphthalene diazonium tosylate as a coupling reagent

Purpose: To present a cost-effective colorimetric method for quantifying artemisinin derivatives, and addressing detection limitations due to their weak chromophoric properties. Methods: The method utilizes 4-nitro-1-naphthalenyldiazonium tosylate as coupling reagent, which reacts with acid-decomposed artemisinin derivatives, forming colored azo adducts, which were optimized for analytical wavelength and detector response. Optimal reaction conditions, like temperature and time, were established, with stoichiometric ratios determined for each analyte. Validation confirmed the method's linearity, precision, accuracy, and limits of detection and quantitation. Results: Artemether, artesunate, and dihydroartemisinin, upon acid decomposition, coupled avidly with diazonium reagent, giving reddish adducts with maximum absorbances at 430, 440, and 430 nm, respectively. Overlaid absorption spectra relative to the reagent and analytes revealed a bathochromic effect. Optimum reaction conditions were established at 50 ⁰C for 15 - 25 min. Assays were linear over 0 - 16 (artemether), 7.33 - 27.33 (artesunate), 6.08 - 16.21 μg/mL (dihydroartemisinin), with limits of detection of 0.21, 0.073, and 0.068 μg/mL, and overall recovery of 100.9 ± 1.7, 101.9 ± 3.3, and 100.4 ± 3.2 %, respectively. The assay results agreed with International Pharmacopoeia methods. Conclusion: This colorimetric approach offers a reliable and sensitive alternative for artemisinin derivative an