A new methodology employing capillary electrophoresis with UV detection (CE-UV) was developed, validated, and applied to determine the presence of cocaine on Brazilian banknotes. Some of the banknotes analyzed were obtained directly from general circulation (well used) while others were collected from Automated Teller Machines (ATMs) (relatively new). The background electrolyte optimized using Peakmaster 5.1 software was composed of 60？mmol？L？1 TRIS(hydroxymethyl)aminomethane and 20？mmol？L？1 2-hydroxyisobutyric acid, at pH 8.4. The separation time achieved for cocaine was only 2.5？minutes. The figures of merit obtained in the evaluation of the proposed method were good linearity ( ) in the concentration range of 0.8–8.0？mg？L？1 and acceptable limits of detection and quantification (0.2？mg？L？1 and 0.8？mg？L？1, resp.). The relative standard deviations of the instrumental precision, repeatability (intraday), and intermediate precision (interday) were less than 4.5% (peak area). The accuracy evaluated through comparing the cocaine results for the banknotes determined by the proposed CE-UV method and using an LC-MS/MS method showed no significant difference between the methods (95% confidence level). In the analysis of the samples cocaine was detected on 93% of the circulating banknotes in amounts ranging from 11.5？μg to 2761.9？μg per note. 1. Introduction Since the 1980s it has been known that banknotes in North America and Europe are contaminated with cocaine residues. This results from the sale and consumption of this drug, because many cocaine users use a wrapped banknote as a kind of straw to inhale the drug. The presence of traces of this drug on banknotes is often used as forensic evidence to establish a connection between a suspect and illicit drugs [1]. Other explanations for the presence of cocaine on banknotes have been proposed, including contamination due to handling during drug dealing, the transfer from a contaminated note to “clean” ones during counting in financial institutions, and also banknotes coming into contact with one another within the ATM [2, 3]. To ensure the determination of cocaine with precision and accuracy, it is necessary to quantitatively extract the drug from the banknotes. In studies reported in the literature, the extraction technique most commonly employed involves the use of organic solvents and a dilute aqueous acid. For the analysis of US dollar banknotes, the solvents chloroform [4, 5], acetonitrile [6], and ethanol [7] have been used, together with procedures involving vortex agitation and centrifugation, followed by
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