Detection of cocaine on euro banknotes; Development of a practical approach for the interpretation of suspect cases.

The presence of traces of narcotics, particularly cocaine, on banknotes in circulation is a known and widespread fact in all countries. While linked to consumption and trafficking (primary contamination), their spread is due to direct contact with other banknotes during machine counting and cash financial transactions. The mere detection of traces of cocaine on a sample of banknotes is therefore not sufficient evidence to establish the banknote's illegal origin. Increasing levels of contamination are recorded close to (in terms of both place and time) the first direct contact with the substance. The analysis must thus be able to demonstrate that the concentration of narcotics on the banknotes is significantly higher (statistically) in terms of value and frequency than would be expected from background noise alone. Even in that event, however, this evidence has to be substantiated with additional confirmations linking banknotes to the person and this latter to drug trafficking and/or dealing. In general, an in-depth and systematic analysis of all seized banknotes to search for traces of narcotics is not only prohibitive in terms of cost, but also unnecessary. If the sampling procedure is respected, the Swiss Federal Supreme Court actually recognizes IMS (ion mobility spectrometry) as a lawful method for checking the degree of banknote contamination, as well as all the statistical conclusions that can be drawn from it. In special cases, the prosecutor may require confirmation of IMS results by a laboratory test (liquid/gas chromatography-mass spectrometry). Using a non-destructive sampling procedure (suction on swabs) we determined the presence of cocaine on 978 circulating euro banknotes, randomly collected at 5 swiss customs offices, with IMS and LC-MS/MS in order to establish a normal (background) contamination level. A significant proportion (46.4%) of the euro banknotes analysed by LC-MS/MS had cocaine concentrations above the quantification limit (1 ng/swab). However, the extent of contamination is a determining factor: 94.6% of the banknotes in circulation have cocaine concentrations equal to or less than 10 ng/swab and only 3.4% have cocaine concentrations above 20 ng/swab. By comparison, only 27.3% and 13.4% respectively of the seized banknotes (2 real cases) had cocaine concentrations equal to or less than 10 ng/swab, but 63.5% and 86.7% respectively had cocaine concentrations above 20 ng/swab. We also describe a Komolgorov-Smirnov test model used to determine the presence of an "abnormal" level of contamination relative to the reference banknotes (banknotes in circulation or background noise) effectively and within realistic practical and theoretical frameworks. This model provides a quantifiable and statistically significant result that not only simplifies data interpretation, but also facilitates admissibility as forensic evidence in proceedings. When applied to the sized banknotes using both IMS and LC-MS/MS data, we obtain fully consistent and sounding conclusions.