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A sensitive square-wave adsorptive cathodic stripping voltammetric method is reported for determining the drug, vildagliptin (VILD), in bulk and commercial formulations with a mean LOD = 1.19 nmol L−1 using a carbon paste electrode (CPE) modified with Ca-montmorillonite clay. The procedure focuses on the formation of a VILD-Cu2+ complex in a bulk solution and the subsequent electrochemical reduction at the modified electrode. The results showed that the modified CPE (95% (w/w) graphite powder and 5% (w/w) Ca-montmorillonite clay) exhibited excellent electrochemical activity toward the investigated VILD-Cu2+ complex. The complex exhibited a well-defined irreversible cathodic peak at − 0.44 V in the Britton–Robinson buffer of pH 7 via acceptance of two electrons and one proton. Under optimal conditions, the VILD concentrations were in the range of 4.0–130 nmol L−1 (R2 = 0.9986) at a fixed concentration of the copper ion. The stability constant (β) and stoichiometric ratio of the complex were determined at 25 °C using electrochemical methods. The structure of the obtained complex was confirmed based on Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy, and thermogravimetric analysis. Our suggested analytical method was applied to determine the IC50 values of VILD and VILD-Cu2+ complex in a human colon cancer (Caco-2) cell line and were found to be 265 and 40 μg mL−1, respectively, using the square-wave voltammetry technique. These IC50 values were in good agreement with those obtained using the thiazolyl blue tetrazolium bromide technique. [ABSTRACT FROM AUTHOR]