A new electrochemical interface based on polyacrylic acid (PAAcid) immobilized in a Nafion® polymeric matrix on graphite screen-printed electrodes for detecting copper is presented. The copper is retained in the surface due to the capacity of the polyacid to chelate metals, and quantified using square wave voltammetry. The response was characterized by spectroscopic techniques (UV-vis-IR), which confirmed the chelation from the Cu.sup.2+ ions by the acid. A calibration curve is presented, showing good linearity and repeatability and its usefulness as a sensor. The range of operation goes from 15 to 50 muM, with a detection limit of 12 muM, making the sensor useful for measurements in environmental samples (after a preconcentration step) and in drinking water.