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- Development and validation of a method for the determination of cocaine and its metabolites in hair using QuEChERS and GC- MS/MSPublication . Brito, Hugo Bernardo Marques Antunes de; Alba, Maria Eugénia Gallardo; Pires, Bruno Miguel Pinheiro; Rosado, Tiago Alexandre PiresCocaine (COC) is one of the most widely consumed illicit stimulants worldwide, with a high addictive potential and severe toxicological effects. Hair analysis offers unique advantages in forensic toxicology, as it allows the documentation of chronic use and, in some cases, acute exposure. In this study, a miniaturised version of the QuEChERS (Quick, Easy, Cheap, Rugged, and Safe) extraction method was developed for the determination of COC and its major metabolites — anhydroecgonine methyl ester (AEME), ecgonine methyl ester (EME), cocaethylene (COET), benzoylecgonine (BEG), and norcocaine (NCOC) — in hair samples. The procedure involved 3 mL of formic acid (5%) in acetonitrile (ACN) and 625 mg of NH4HCO2 as solvent and partitioning salt, respectively, followed by a dispersive solidphase extraction (d-SPE) step using 175 mg of MgSO4 and 55 mg of primary secondary amine (PSA). Samples were analysed by gas chromatography coupled to tandem mass spectrometry (GC-MS/MS). Following optimisation through design of experiments (DoE), the method was validated according to the guidelines of the Society of Hair Testing (SOHT). The working range was set at 0.05–5 ng/mg for all analytes, except AEME (0.5–5 ng/mg). Recoveries ranged from 20–29% (AEME), 24–27% (EME), 33–42% (COC), 43–77% (COET), 25– 48% (BEG), and 27–37% (NCOC). The method was successfully applied to authentic hair samples, in which COC was detected in almost all cases, often accompanied by metabolites at concentrations above the lowest limit of quantification (LLOQ). The µ-QuEChERS method proved to be a sustainable, sensitive, and multi-analytical approach for the determination of cocaine and metabolites in hair, with strong potential for application in clinical and forensic toxicology.