Voltammetric determination of sulfamethoxazole using commercial screen-printed carbon electrodes

[Display omitted] •Commercial screen-printed electrodes were applied to voltammetric sensing of sulfamethoxazole.•Optimal results were obtained at pH 5.5, with an irreversible oxidation of SMX involving 2e−/2H+.•LOD 15 µg/L and linear range 50–600 µg/L achieved, with good repeatability and reproducibility.•Method sensitive to different sulfonamides with a free amino terminal group.•A spiked tap water sample was successfully analyzed with a good recovery. A differential pulse voltammetric (DPV) method using commercial screen-printed carbon electrodes (SPCE) is developed for a fast and cost-effective determination of the antibiotic sulfamethoxazole (SMX). Optimal measurements are carried out at pH 5.5 in acetate buffer and yield a detection limit of 15 µg/L and a linearity range of 50 – 600 µg/L with good repeatability (1.1%) and reproducibility (2.5%). The method is successfully applied to the analysis of a spiked tap water sample with very high reproducibility (0.4%) and good trueness (Recovery 95.2%). Additional considerations are made about the irreversible electrochemical oxidation of SMX, which is notoriously pH-dependent according to a process involving 2e- and 2H+, in agreement with several reported mechanisms in the literature. Besides, the analysis of other sulfonamide antibiotics is discussed, showing the key role of the free terminal amino group in oxidation, which makes almost undistinguishable voltammetric signals from different molecules sharing this moiety. In contrast, the acetylation of the mentioned group (e.g., in sulfonamide metabolites) drastically reduces the sensitivity of voltammetric measurements.