Phenylurea herbicides are persistent contaminants, which leads their transport to the surface and ground waters, affecting human and aquatic organisms. Different analytical methods have been reported for the detection of phenylureas; however, several of them are expensive, time-consuming, and require complex pretreatment steps. Here, we show a simple method for the simultaneous electrochemical determination of two phenylurea herbicides by differential pulse adsorptive stripping voltammetry (DPAdSV) using a modified platinum/chitosan electrode. The one-step synthesized platinum/chitosan PtNPs/CS was successfully characterized by TEM, XRPD, and FT-IR, and applied through the sensing platform designated as PtNPs/CS/GCE. This bio-based modified electrode is proposed for the first time for the individual and/or simultaneous electrochemical detection of the phenylurea herbicides diuron and isoproturon compounds extensively used worldwide that present a very similar chemical structure. Electrochemical and interfacial characteristics of the modified electrode were evaluated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that the oxidation mechanism of diuron and isoproturon occurs in two different pathways, with a peak-to-peak definition of ca. 0.15 V. Under differential pulse adsorptive stripping voltammetry (DPAdSV) optimized conditions, the limit of detection (LOD) was estimated as 7 μg L^-1 for isoproturon and 20 μg L^-1 for diuron (E_d = +0.8 V; t_d = 100 s). The proposed method was successfully applied to the determination of both analytes in river water samples, at three different levels, with a recovery range of 90-110%. The employment of the bio-based sensing platform PtNPs/CS/GCE allows a novel and easy analytical method to the multi-component phenylurea herbicides detection.

An electrochemical sensor based on carbon paste modified with polyethyleneimine was developed and employed for the determination of caffeic acid in aromatic herbs. The sensor was prepared by mixing polyethylenimine (1.5% v/v), graphite powder, and mineral oil. The polyethylenimine-based electrode showed an enhancement of charge transfer at the electrode–solution interface and a higher current intensity for the electrochemical reaction of caffeic acid, in comparison to the unmodified electrode. The calibration plot of caffeic acid constructed in 0.1 mol L⁻¹ acetate buffer (pH 5.0) by square wave voltammetry was linear in the range of 1.25 to 19.9 μmol L⁻¹ with a limit of detection of 0.13 μmol L⁻¹, respectively. Finally, the proposed sensor was employed to monitor the caffeic acid with accuracy in dried Thymus vulgaris and Salvia officinalis samples, with recovery results from 93 to 105%.