Among the drugs of abuse, cocaine (COC) is the second most commonly used worldwide due to its stimulating and psychoactive effects. Currently, this drug is classified, according to the World Drug Report (WDR), as an illicit substance and is frequently seized by law enforcement agencies. Additionally, it can cause social problems due to its abusive use. This study describes the development of an electroanalytical methodology using square wave voltammetry (SWV) associated with a single electrode of carbon paste modified with 10 % MWCNTs (multi-walled carbon nanotubes) to quantify COC in seized samples containing up to 20% cocaine (low purity index) in the state of Espírito Santo (Brazil). SWV parameters, including Es = 10 mV, a = 30 mV, and f = 15 Hz, were optimized utilizing a Britton-Robinson buffer solution of 0.1 mol/L (pH 10) as a supporting electrolyte through the implementation of experimental design (CCD). COC showed an oxidation peak at approximately 1.0 V, with low limits of quantification and detection (1.90 × 10−6 mol L−1 and 5.75 × 10−7 mol L−1, respectively), in the linear range from 2.36 × 10−6 mol L−1 to 1.38 × 10−5 mol L−1, with the proposed methodology. Thus, this research develops a fast and low-cost technique in favor of the police, allowing the R2 = 99%. The results obtained in the intraday calibration curves present a relatively low standard deviation (RSD < 8%), indicating a good repetition of the value production of an electrode for less than USD 1.42 per analysis.