On-site forensic analysis of colored seized materials: Detection of brown heroin and MDMA-tablets by a portable NIR spectrometer

Abstract

The increasing workload for forensic laboratories and the expanding complexity of the drug market necessitates efficient approaches to detect drugs of abuse. Identification directly at the scene of crime enables investigative forces to make rapid decisions. Additionally, on-site identification of the material also leads to considerable efficiency and cost benefits. As such, paperwork, transportation, and time-consuming analysis in a laboratory may be avoided. Near-infrared (NIR) spectroscopy is an analysis technique suitable for rapid drug testing using portable equipment. A possible limitation of spectroscopic analysis concerns the complexity of seized materials. NIR measurements represent composite spectra for mixtures and diagnostic spectral features can be obscured by excipients such as colorants. Herein, a NIR-based (1300-2600 nm) detection of heroin and MDMA in colored casework (i.e., brown powders and ecstasy tablets) using a portable analyzer is presented. The application includes a multistage data analysis model based on the net analyte signal (NAS) approach. This identification model was specifically designed for mixture analysis and requires a limited set of pure reference spectra only. Consequently, model calibration efforts are reduced to a minimum. A total of 549 forensic samples was tested comprising brown heroine samples and a variety of colored tablets with different active ingredients. This investigation led to a >99% true negative and >93% true positive rate for heroin and MDMA. These results show that accurate on-site detection in colored casework is possible using NIR spectroscopy combined with an efficient data analysis model. These findings may eventually help in the transition of routine forensic laboratories from laboratory-based techniques to portable equipment operated on scene.

Keywords: colored samples; forensic casework analysis; illicit drug analysis; near-infrared spectroscopy; portable devices.

FIGURE 1

Second derivative NIR spectra of heroin base (black trace in a and b) compared with common adulterants (a) and various brown heroin casework samples (b). (a) Paracetamol (red), caffeine (green). (b) Brown heroin samples (brown to orange shades), brown heroin sample highly adulterated with paracetamol and caffeine, H19 (red). (c) Heroin HCl·H2O (purple) and a white heroin casework sample, H8 (blue) [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 2

Second derivative NIR spectra of MDMA HCl (black trace in all panels) compared with other drugs (a), common excipients (b), and various MDMA‐containing casework samples (c). (a) Methamphetamine HCl (red), cocaine HCl (green), ketamine (blue), amphetamine sulfate (orange). (b) Microcrystalline cellulose (red), lactose (green), mannitol (blue), Mg stearate (orange). (c) MDMA crystals, M1‐3 (orange shades), crushed MDMA‐containing ecstasy tablets, P1‐4 (purple to red shades) [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 3

Normalized (raw) diffuse reflection NIR spectra of hydrated MDMA HCl crystals (black trace) and anhydrous MDMA HCl (red trace) [Colour figure can be viewed at wileyonlinelibrary.com]

FIGURE 4

VIS‐NIR spectrum of crushed MDMA‐containing ecstasy tablets. Plots in (a) were correctly identified as MDMA‐containing. Plots in (b) are samples with a false negative result on the MDMA matrix libraries. (a) P1 (gray); P9 (yellow); P13 (pink); P16 (red); P18 (purple); P25 (blue); P37 (green), and pure MDMA HCl hydrate (black). (b) P19 (yellow) and P30 (dark gray); the plot colors correspond with the actual color of the ecstasy tablets. [Colour figure can be viewed at wileyonlinelibrary.com]