Abstract
The use of chemical analysis of fingerprints as an alternative approach for drug testing has become subject of recent publications. However, the significance of the detection of drugs in fingerprints compared to a background population of non-drug users has not yet been explored. In this research, the main area of research was to determine the forensic potential of detecting cocaine and heroin use through the analysis of fingerprints. Fingerprint samples deposited on paper were extracted using an extraction solution (10% dichloromethane in methanol) and analysed using liquid chromatography – mass spectrometry (LC-MS). This research showed that cocaine and benzoylecgonine were detected in 100 and 94% of natural fingerprint samples (n= 65) collected from drug users, and similarly, heroin and 6-acetylmorphine were detected in 98 and 100% of samples (n = 60). Cocaine and benzoylecgonine were also detected in 13 and 5% of natural fingerprints (n = 98) from a background population of non-drug users. In contrast, heroin and 6-acetylmorphine were detected in 0 and 1% of fingerprints from the background population. For cocaine, a threshold level was required to differentiate fingerprints from drug users and environmental exposure in non-drug users (at a ratio analyte (A) to internal standard (IS) 0.015). The analytes of interest could still be detected in fingerprint samples from drug users after a hand cleaning procedure, however this resulted in a lower detection rate compared to natural fingerprints. In contrast, the analytes were not present in fingerprints collected from non-drug users after handwashing (1% false positive rate for cocaine). Furthermore, cocaine, benzoylecgonine, heroin and 6-acetylmorphine can also be detected in fingerprint samples from dermal contact with the parent drug even after the use of hand cleaning procedures. The detection of illicit drugs in fingerprints is therefore not solely indicative of administration of a drug but does indicate that these analytes are not prevalent in a background population of non-drug users. Additionally, the detection of isoniazid and acetylisoniazid in fingerprint samples from tuberculosis medication showed the potential application of fingerprint testing to monitor adherence to drug treatments. The detection window of isoniazid and acetylisoniazid (<2 days) suggests that a fingerprint may confirm when a patient stops complying to their treatment. This demonstrates that a fingerprint test could confirm non-adherence to treatment, which can be used to help improve treatment plans for patients and improve success rates. Furthermore, the presence of cocaine and benzoylecgonine in urine and saliva collected from drug users was determined using portable mass spectrometry to show the potential for on-site sample analysis for drug testing. Previous work has shown that illicit drugs can be detected in fingerprints, however the suitability of fingerprints for drug testing (namely cocaine and heroin use) has not yet been explored. This research provides information on the influence of the fingerprint sampling strategy, presence of contact residue and transfer of drugs between individuals. These aspects are important to consider in relation to the stages of fingerprint testing and highlight its strengths and weaknesses for further applications (e.g. workplace drug testing, rehabilitation centres and hospitals). To improve fingerprint testing, further work is required on the standardisation of a fingerprint collection procedure, including validation procedures.