Performance evaluation of handheld Raman spectroscopy for cocaine detection in forensic case samples

Abstract

Handheld Raman spectroscopy is an emerging technique for rapid on-site detection of drugs of abuse. Most devices are developed for on-scene operation with a user interface that only shows whether cocaine has been detected. Extensive validation studies are unavailable, and so are typically the insight in raw spectral data and the identification criteria. This work evaluates the performance of a commercial handheld Raman spectrometer for cocaine detection based on (i) its performance on 0-100 wt% binary cocaine mixtures, (ii) retrospective comparison of 3,168 case samples from 2015 to 2020 analyzed by both gas chromatography-mass spectrometry (GC-MS) and Raman, (iii) assessment of spectral selectivity, and (iv) comparison of the instrument's on-screen results with combined partial least square regression (PLS-R) and discriminant analysis (PLS-DA) models. The limit of detection was dependent on sample composition and varied between 10 wt% and 40 wt% cocaine. Because the average cocaine content in street samples is well above this limit, a 97.5% true positive rate was observed in case samples. No cocaine false positives were reported, although 12.5% of the negative samples were initially reported as inconclusive by the built-in software. The spectral assessment showed high selectivity for Raman peaks at 1,712 (cocaine base) and 1,716 cm −1 (cocaine HCl). Combined PLS-R and PLS-DA models using these features confirmed and further improved instrument performance. This study scientifically assessed the performance of a commercial Raman spectrometer, providing useful insight on its applicability for both presumptive detection and legally valid evidence of cocaine presence for law enforcement.

Fentanyl detection and quantification using portable Raman spectroscopy in community drug checking

“…For a preliminary assessment of these parameters, a 10-fold cross-validation was performed. [39,47] Final choices however were guided by minimization of the rootmean-square error of prediction (RMSEP) and the principles of parsimony, where appropriate. [36,46,[48][49][50] Hotelling's T 2 and Q residuals were used to explore potential calibration outliers.…”

“…Simulated street drugs, or those seized by law enforcement, have also been tested using Raman spectroscopy. [37][38][39] Additional challenges present themselves in shifting these technologies for use in a community-based harm reduction service. [40] For example, the consequences of low-concentration adulterants are less predictable than what may be encountered in pharmaceutical quality control applications.…”

A calibration friendly approach to identify drugs of abuse mixtures with a portable near‐infrared analyzer

“…Examples of fluorescent compounds include paracetamol and MDMA. Especially when mixed with other compounds (e.g., cocaine adulterated with paracetamol), this may limit the analysis of mixtures 16,21,22 . Several commercially available handheld Raman spectrometers can currently be used for presumptive testing of forensic samples, although the relatively high instrument price (30–80 k€) will limit their broad applicability in a law enforcement and crime scene setting.…”

Raman Scattering-Based Biosensing: New Prospects and Opportunities

“…The choice of a suitable laser avoiding fluorescent interference depends on the molecule to be identified. A number of studies have proven the effectiveness of handheld spectrometers for the detection of drugs [ 208 , 209 , 210 ] and different toxins [ 211 ]. Going forward, the miniaturization of equipment has also affected nonlinear optical microscopy techniques, CARS microscopy, and SRS microscopy.…”