Heroin can be detected on banknotes by a rapid procedure that permits the analysis of hundreds of notes per hour. The method enables the large-scale comparison of seized currency to that in general circulation to establish an association with criminal activity.

It seems that everyone nowadays can recite the cocaine/banknote fact at parties: "every US banknote note in circulation is contaminated with cocaine", although this is not exactly true. It takes a few exchanges of a brand new note with used notes for contamination to reach the general level.

The situation is almost as severe in the UK, where up to 80% of the paper currency in circulation (but 99% in the London area) was estimated to be contaminated with drugs in general, and cocaine in particular. Some notes are so dirty that they are destroyed as a health measure. The other main drugs that have been found on banknotes are heroin, ecstasy and cannabis.

The UK organisation Mass Spec Analytical Ltd. (MSA) developed a technique in 1997 for detecting drugs on banknotes and other media like clothing and dust and reported on many different applications at the 2001 ASMS meeting, as described in Fragments. Since then the technique has been refined and used to provide forensic evidence in court cases. Now, they have used the technique to analyse heroin-contaminated notes, with co-researcher Richard Brereton from the School of Chemistry at the University of Bristol.

When bundles of banknotes are seized in drug-related crimes, their analysis can lead to one more piece in the prosecutor's armoury, if they can be shown to have more drug on them than others in general circulation. Much of the cocaine contamination comes from using banknotes to take the drug, whereas heroin contamination generally arises by direct contact with the notes or by secondary transfer via drug-contaminated surfaces.

Cocaine is easily transferred from one note to another, and is relatively stable, but heroin is stickier and is easily hydrolysed by moisture. So banknotes in general circulation are likely to have low heroin levels and the presence of comparatively high levels would appear to suggest recent contact with the drug.

The methodology, described in Rapid Commun. Mass Spectrom. 2005, 19, 2137 by senior reporter James Carter, is based on a thermal desorption unit (pictured) linked to a triple quadrupole mass spectrometer. A single note is placed between the hot blocks (285 °C) of the unit for one second. The debris on the surface is desorbed and carried rapidly into the mass spectrometer by a stream of lab air where the compounds are ionised by atmospheric pressure chemical ionisation (APCI) tandem mass spectrometry (MS/MS).

If it appears simple, that's because it is. The short heating times remove sufficient material from the notes without destroying them, an important consideration in forensic work. Analysis was based on the detection of diacetylmorphine (DAM), the major active component of heroin. In MS/MS, two product ions (m/z 328 and 268) from the protonated molecular ion (m/z 370) were required to be present within certain intensity ratios for a "positive" result.

Carter told Fragments that around 500 notes can be analysed in one hour, including the strict paperwork that is required for train of evidence. However, even at this speed, the analyst can see the response on the instrument's data system before inserting the next note. By comparison, a typical GC/MS analysis of 500 notes would take about 170 hours.

Background levels of DAM on notes in general circulation were determined over 5 years by analysing 48 batches (13,159 banknotes) that were collected from banks at different locations in the UK. Both ends of each note were analysed to give a more accurate value, leading to an average figure of 2.26% of all notes being contaminated with DAM (range 0-5.71%).

This distribution was modelled using two data transformations, an arcsin (square root) and a lognormal distribution, which gave the same results: a maximum contamination level of 9-10% for notes in general circulation. So any batches of banknotes found with a higher percentage of contamination can be regarded as highly suspicious.

The method was applied to 422 banknotes, representing about 33% of a seized batch, selected from the top, middle and bottom of the bundles. In this case, all notes were inserted in blocks in the same orientation and only one end was analysed, in order to preserve the evidence on the other end for later analysis if required. The proportion of the seized notes contaminated was far greater than for those in general circulation.

In routine drug analysis work, MSA test for the presence of four drugs or drug components, Carter told Fragments. Tetrahydrocannabinol (cannabis), cocaine, MDMA (ecstasy) as well as DAM (heroin) are the main targets, although other drugs such as amphetamine or cutting agents such as caffeine can be added as required. The rapid analytical technique ensures the accurate analysis of banknotes and is easily adapted to the analysis of drugs found on other surfaces such as mobile phones, car interiors and house furniture.

Related links:

• The Observer on contaminated banknotes
• Mass Spec Analytical Ltd.
• Fragments on drug analysis by thermal desorption
• School of Chemistry, University of Bristol
• Rapid Commun. Mass Spectrom. 2005, 19, 2137

Article by Steve Down