Safety Screening and Marker-Based Quality Assessment of Commercial Aucklandia costus (Mu Xiang) by LC–MS/MS

Background/Objectives: Aucklandia costus (Mu Xiang) is a widely used herbal product whose vernacular name is also applied to Aristolochia species. Aristolochia contains nephrotoxic and carcinogenic aristolochic acids, and misidentification can therefore contaminate costus products. This study aimed to develop and validate a liquid chromatography–tandem mass spectrometry (LC–MS/MS) method to screen for aristolochic acid I and quantify the quality markers costunolide and dehydrocostus lactone in one run. Methods: Ultrasonic-assisted extraction with 50% aqueous ethanol was followed by LC–MS/MS using an ethanol-based mobile phase, with all analytes eluting within 4 min. The method was validated following International Council for Harmonisation guidelines, tested on A. costus mixed with Aristolochia indica, and applied to 40 commercial A. costus samples from the Saudi market. Results: Aristolochic acid I (limit of detection 0.02 µg/L) remained detectable at 10% w/w Aristolochia adulteration but was not detected in any commercial sample. Total costunolide and dehydrocostus lactone content ranged from 0.19% to 1.82% w/w, against 2.10% in the authenticated reference, and only one sample met the 1.8% w/w minimum of the Chinese Pharmacopoeia. Conclusions: The absence of aristolochic acid I did not guarantee product quality. Combining aristolochic acid I screening with marker quantification in one run offers a promising quality-control tool for costus products, although other aristolochic acid congeners were not screened.