The Experimental Design Approach in Square‐Wave Voltammetric Determination of Tamoxifen by NiO‐CPE**

Abstract Due to the explosive global increase of various cancers, the need to introduce/develop novel catalysts/sensors for quantitative determination of cancer drugs is emphasized. Nickel oxide nanoparticles (NiO‐NPs) calcined at 200 °C were used as a modifier of carbon paste electrode (CPE) to quantify tamoxifen (TAM) in an aqueous solution. The square wave voltammetry (SqW) was used due to its high sensitivity. The modified NiO‐CPE showed an SqW anodic peak current with a peak potential of about 420 mV in the NaOH‐supporting electrolyte. This peak current was decreased when TAM analyte was added to the test solution. Thus, this reduced peak current (Δi) was used to quantify TAM in solution. The experimental design used the response surface methodology (RSM) approach to study the simultaneous interaction effects between the influencing variables. The optimized run was associated with a 10 % NiO ingredient in the CPE, 0.3 M NaOH, an amplitude of 200 mV, a step potential of 3 mV, and a frequency of 25 Hz. A proportional behavior was obtained between the mentioned Δi and TAM concentration in the range of 10–60 nM. The detection (LOD) and quantification (LOQ) limits were 1.81±0.35 and 6.05±0.24 nM, respectively. Interfering and recovery results confirmed the applicability of the proposed NiO‐CPE electrode for TAM determination in complex matrixes and the direct assay of the drug in human serum.