Electrochemical Characterization of Common Cutting Agents Found in Illicit Drugs

Abstract

Nationwide use of illicit drugs has continued to rise over the last few decades, with more than a two-fold increase in global seizures from 2016 and 2020. Most seized drug samples are complex mixtures of drugs and cutting agents, which can complicate the detection and quantification of the illicit drugs in the sample. The presence of these cutting agents can however be beneficial for source tracing purposes, as the majority of cutting agents are selected based on availability in the area where the bulk drug was prepared. The goal of this work was to conduct a systematic study of the electrochemical characteristics of the most common cutting agents found in illicit drugs using unmodified, commercially available glassy carbon electrodes. The long-term goal is to establish an extensive database of electrochemical characterizations of cutting agents and illicit drugs encountered by law enforcement using unmodified, commercially available electrodes to help expand the developing field of forensic electrochemical analyses. This database could then be referenced for the identification of unknown samples to determine the presence of possible illicit drugs and cutting agents that are present to help guide the analyst in further testing. The standard methods for drug detection include a combination of laboratory testing and field-deployable assays ranging from colorimetric tests to gas chromatography-mass spectrometry instrumentation. These detection methods, as well as relevant literature were investigated in Chapter 1. The most used screening methods for illicit drugs are colorimetric tests; however, these assays are prone to false positives. Chapter 1 introduces the existing applications and current research efforts in forensic electrochemistry by describing relevant electrochemical sensors and methods and examining in particular their performance regarding accuracy, sensitivity, and low-cost claims. This overview highlights the broad possibilities of electrochemical analysis in forensics as well as the opportunities when applied to detection and quantification of illicit drugs, demonstrating the current needs for more systematic and consistent characterizations of cutting agents found in seized-drug samples. Chapter 2 details the material, reagents, and experimental conditions, showing their simplicity, and the standard electrochemical and preparative equipment used geared towards an easy implementation in any analytical laboratory. Chapter 3 describes the systematic voltametric characterizations performed on thirteen common cutting agents: phenacetin hydrochloride, levamisole hydrochloride, diphenhydramine hydrochloride, quinine, acetaminophen, ascorbic acid, caffeine, lactose, inositol, mannitol, glucose, sodium bicarbonate and calcium carbonate. In addition to the common, information-rich cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) were used as these pulsed electroanalytical methods are typically considered more sensitive than CV and often employed for quantitative analyses of species present at low concentrations (Chapter 3). Overall, DPV resulted in voltammograms with peaks shaped closer to the ideal redox peaks, also referred to as ‘better defined’, thus enhancing the analytical performance of the assay. For example, In the analysis of diphenhydramine hydrochloride, DPV permitted the measurement of an oxidation with a peak displayed at 1.0 V vs Ag/AgCl, which was not observable when performing CV or SWV. On the other hand, SWV provided noticeably greater intensities of peak current, which allowed for a better detection of the difficult-to-observe redox reactions of quinine occurring at -0.4, 0.0 and 0.4 V vs Ag/AgCl. Some chemical species when present in seized drugs can alter the pH of the tested samples, such as ascorbic acid. Changes in pH will impact the redox activity of the pH-dependent electroactive species present in a sample, thus we investigated how pH of the solvent affected the observation of the redox peaks of those susceptible cutting agents, namely ascorbic acid, quinine, diphenhydramine hydrochloride, and levamisole hydrochloride (Chapter 4). Of particular interest was a significant change in the electrochemical characterization of these species when the pH was varied around their pKa values. Additionally, the composition of the solvent, or supporting electrolyte (SE) solution, can in some cases result in interactions with the analytes in the sample; the study of caffeine with different SE in Chapter 4 illustrates this situation. Specifically, sulfuric acid was the most suited SE of those tested for caffeine analysis. The impact of successive voltametric scans, on the analysis of chemical species were also investigated, using acetaminophen and quinine, demonstrating the development of additional redox peaks in some situations that could provide additional elements towards a more individualized electrochemical profile for cutting agents (Chapter 4). The influence of the material of the working electrode on the electrochemical characterization of cutting agents was explored. Solutions of ascorbic acid, acetaminophen, quinine, and diphenhydramine hydrochloride were electrochemically characterized using a glassy carbon and a platinum working electrode, while ascorbic acid was also characterized on gold and silver electrodes. These examples demonstrate the adaptability of this electroanalytical method with various commonly used electrodes. (Chapter 4). In Chapter 5, we applied similar electrochemical method to the identification of cutting agents and illicit drugs in two-component mixtures. Specifically, these trials included mixtures of fentanyl with a cutting agent at a relative ratio of 1 : 100, using as cutting agents ascorbic acid, diphenhydramine hydrochloride, or glucose, demonstrating the ability of this simple electrochemical method using common commercial electrodes to simultaneously detect illicit drugs and cutting agents.