An electroanalytical methodology was developed for the direct determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) using a graphite-polyurethane composite electrode and square wave voltammetry (SWV). 2,4-D exhibited one reduction peak with characteristics of an irreversible process at ？0.54？V (versus Ag/AgCl), which is controlled by the diffusion of the reagent on the electrode surface. After the experimental parameters optimization (pH 2.0, ？s？1, ？V, and ？V), analytical curves were constructed in the range of 0.66？mg？L？1 to 2.62 ？mg？L？1. Detection (LD) and quantification (LQ) limits were 17.6？ g？L？1 and 58.6？ g？L？1, respectively. The methodology was successfully applied to measure the percolation of the herbicide 2,4-D in undisturbed soil columns of different granulometric compositions. 1. Introduction 2,4-D (2,4-Dichlorophenoxyacetic acid) is one of the most widely used herbicides in the world and is characterized as low-cost, quite efficient even at low concentrations, and moderately hazardous (class II) according to the World Health Organization [1]. Although this herbicide easily moves though the soil, its leaching into the groundwater can be minimized due to the degradation by microorganisms and also the absorption by plants. Its primary route of degradation in the environment is by microorganisms, which increases with temperature, humidity, pH, and organic matter content [2, 3]. In Brazil, the maximum acceptable concentration of 2,4-D in water is 4.0？ g？L？1, according to resolution 357 of the Brazilian National Environment Council [4]. Several chromatographic [5–9] and immunoassay methods [10–13] have been used to determine 2,4-D in biological and environmental matrices. However, chromatographic methodologies are time-consuming due to the derivatization step and complex extraction procedures. Immunoassay methods use biological subtracts that may present poor stability and in some cases result in low repeatability of the analytical signals for a long analysis interval [14]. Electroanalytical procedures have been successfully applied for the determination of inorganic and organic compounds, including pesticides, in many environmental matrices, due to their good sensitivity, short time analysis, low-cost, and the possibility of sample analysis without extractions or pretreatments [15–17]. It is well known from the literature that 2,4-D exhibits poor electroactivity on most common electrode material surfaces, such as carbon, platinum, and mercury [2]. For this reason, it is crucial to develop modified electrodes for the determination
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