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Introduction: Nutricosmetics derived from Silybum marianum, known for their anti-inflammatory and hepatoprotective properties, necessitate accurate quantification of silybin, a key bioactive component., Objectives: This study aims to develop a novel high-performance liquid chromatography (HPLC) method with amperometric detection (HPLC-ECD) for the precise determination of silybin. An ultrasound-assisted extraction (UAE) procedure is also established for solid sample preparation prior to chromatographic analysis., Materials and Methods: Chromatographic separation of silybin was performed on a C18 column and using methanol-0.035 M potassium phosphate (pH 4.0) at 1.0 mL min -1 flow rate as mobile phase in gradient mode. The electrochemical detection (ECD) of silybin was carried out on a glassy carbon electrode (GCE) at +1.10 V versus Ag/AgCl. The UAE procedure for silybin extraction from solid samples was performed by 15 min sonication in an ultrasonic bath (80 kHz and 100% power) at room temperature., Results: Under the optimal chromatographic conditions, silybin diastereoisomers (silybin A and silybin B) can be separated from other S. marianum flavonolignans in less than 20 min, with a detection limit (LOD) of 0.060 mg L -1 and a reproducibility (RSD) of 5%. This method was successfully applied to analyze silymarin-containing products with recoveries close to 100%., Conclusions: This work presents the first HPLC method for silybin determination using an amperometric detector with a GCE. The LOD is competitive in comparison with previously published HPLC-DAD methods. This HPLC-ECD method allows silybin diastereoisomers identification without interferences of other flavonolignans present in silymarin extracts., (© 2024 The Author(s). Phytochemical Analysis published by John Wiley & Sons Ltd.)