LCMS Method for the Determination of Illicit Drug Residues on Paper Currency

Lockie C. Ieong, Stanley D. Menacherry, Frederick P. Smith


A simple, sensitive, and specific method was developed for determination of cocaine-related substances, amphetamine-like stimulants, caffeine, and ketamine residues on paper currency. The method comprises of solvent extraction, solid phase cleanup and concentration, liquid chromatography separation, and ESI mass spectrometric detection in MRM mode (LCMS). Assay parameters showed high specificity, sensitivity, and excellent accuracy and precision. The assay had a sufficient dynamic concentration range to capture the large variation in residues observed on test samples. The LLOQ for the injected extract was 5 ng/mL for all analytes except for caffeine (50 ng/mL). Converted to the lowest quantifiable amount on a single banknote, this calculated as 2.5 ng of each analyte (25 ng for caffeine). Co-extracted substances from the banknotes were found to enhance the analyte signal in electrospray ionization. Enhancement ranged from 140% for caffeine to 480% for ketamine. The LCMS method was successfully applied to the analysis of banknotes originating from Macao, China. Banknotes were collected from four major metropolitan areas in Macao. Four or more drug residues were detected on the majority of the currency notes samples. Ketamine was the predominant analyte detected (98%), followed by methamphetamine (96%), cocaine (95%), metabolite benzoylecgonine (87%), methamphetamine/caffeine combination (“Magu”) (91%), and MDMA (14%).

Interestingly, ketamine was the predominant illicit drug detected on Macao banknotes. This was unexpected as ketamine is not known to be generally popular with the locals. The residue patterns demonstrate the role of external influences on illegal drug-use. Macao’s gaming-based economy attracts tourists from mainland China and surrounding regions such as Taiwan, Malaysia, Indonesia, and Hong Kong. Gaming attracts individuals who are thought to exceed the general population's average for controlled substance abuse and trafficking. These findings indicate that environmental residues of illicit drugs should be taken into account when interpreting drug testing results.

Keywords: Macao, China, Pataca, international drug trafficking, gambling, ketamine, Magu, LC-MS/MS, drug testing, contamination, signal enhancement, forensics

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