Straightforward screening of ketamine in forensic samples using voltammetry with screen-printed carbon graphite electrodes

Abstract

Ketamine (KET) is a controlled psychoactive substance widely misused for its stimulant and dissociative effects. Known by street names such as "Special-K," "Happy Water," "K Powdered Milk," "Pink Cocaine," and "Party Lollipops," its growing prevalence in illicit drug markets has raised significant public health and forensic concerns. In this work, an electrochemical method was developed for the selective and straightforward detection of KET in forensic samples using screen-printed carbon graphite electrodes (SPE-Gr) and differential pulse voltammetry (DPV). KET exhibited two oxidation peaks and, for the first time, three distinct reduction processes on a working electrode surface. Two of these cathodic peaks enable reliable differentiation of KET from several other drugs. The optimized method, based on Britton-Robinson buffer (0.1 mol L^-1, pH 7.0), produced highly reproducible responses, with relative standard deviations (N = 3) below 3.0 % for peak currents and below 1.0 % for peak potentials. Linear dynamic ranges were established for oxidation (3.7-54 μmol L^-1) and reduction (15-100 μmol L^-1) processes, with corresponding detection limits of 0.5 μmol L^-1 and 4.5 μmol L^-1. Interference studies confirmed the method's ability to discriminate KET from major interfering substances, including MDMA (ecstasy), MDA, amphetamine, methamphetamine, and cocaine. The approach also demonstrated reliable detection of KET in reference material certified by the United Nations Office on Drugs and Crime (UNODC), in addition to demonstrating excellent performance in the analysis of seized street samples. Overall, the proposed method is well-suited for straightforward, selective, and portable screening of KET in forensic contexts.

Keywords: Forensic investigation; Portable sensors; Presumptive tests; Street drugs; Stripping voltammetry.