Forensic Electrochemistry: A Dual-Mode Strategy for Rapid and Selective Detection of Catecholamine Compounds

A novel colorimetric-electrochemical strategy was developed for the selective detection of catecholamine compounds, with application to the analysis of epinephrine (EPN) in forensic samples as a proof-of-concept. The method integrates a colorimetric step (Melo Test), based on ferricyanide oxidation in alkaline medium (ammonium buffer), with a two-stage electrochemical protocol employing screen-printed graphite electrodes (SPE-Gr). Three analytical responses are obtained: (i) the oxidation peak of EPN before the colorimetric reaction (O1); (ii) a distinct reddish-orange color following a positive Melo Test for catecholamine structures; and (iii) a new oxidation signal (P1) corresponding to the reaction product. The combined response also enabled discrimination between β-hydroxylated catecholamines and structurally related catecholamines lacking this functionality. The method was optimized using square-wave voltammetry, demonstrating good linearity (6 to 60 μg L-1), low limits of detection (1.5 and 2.3 μg L-1 for O1 and P1, respectively), and high reproducibility (RSD <5% for Ep and Ip). Application to biological matrices (urine, serum, saliva, and vitreous humor) yielded high recoveries, negligible matrix effects, and high selectivity even in the presence of structurally related compounds (18 substances individually and in mixtures). This approach offers a reliable tool for EPN screening in forensic toxicology, with potential extension to other catecholamine analytes.