Scientists have developed a new weapon for the war on drugs: a novel method for tracing the illicit substances on currency. Study results indicate that the pattern of contamination on money recovered from drug-related crime scenes is significantly different than that seen on notes in regular circulation.

Previous studies had revealed that many bank notes around the world contain trace amounts of cocaine, but contamination with other controlled substances is still relatively rare. In the new work, Karl Ebejer of Mass Spec Analytical Ltd. in Bristol, U.K., and his colleagues analyzed currency using mass spectrometry to look for a fingerprint of the chemical diacetylmorphine (DAM), an active component of heroin. The researchers exposed money recovered in a police raid to high temperatures that cause many compounds to vaporize. The gas was then fed into a mass spectrometer, which separates fragmented chemicals according to mass. Because certain chemicals routinely break into the same fragments, scientists can determine which molecules were present by searching for specific pieces. For example, to identify DAM on the bank notes, the team searched for two particular ions.

The new approach is sensitive enough to allow analysis of single bills, an improvement over other methods that must test entire bundles at once to detect what might be very small amounts of chemicals. Identifying more individual bills that are contaminated reduces the likelihood that a person came into possession of them by chance, the authors argue. "The association doesn't prove guilt," Ebejer cautions, "but cries out for an explanation. If a defendant can offer no reasonable explanation as to why they possess a large quantity of cash and why this cash is highly contaminated with heroin, a jury must draw its own conclusions." The findings appear in the latest issue of the journal Rapid Communications in Mass Spectrometry.

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