Application of the response surface methodology for the optimization of cadmium quantification in cocoa samples from the Caquetá and Santander departments using anodic stripping voltammetry

The electrochemical behavior of the bismuth ion (Bi³⁺) was studied on glassy carbon (GC) and gold (Au) electrodes using cyclic voltammetry (CV). For both electrodes, the redox process of Bi³⁺ was found to be quasi-reversible, with cathodic peak potentials of 0.10 V and -0.16 V for the reduction of Bi³⁺ to Bi⁰ on Au and GC electrodes, respectively. For the GC electrode, the peak current ratio (Ipa/Ipc) was four times higher than that of the Au electrode in 0.1 M hydrochloric acid (HCl). Additionally, a Box-Behnken design and a central composite design were implemented to optimize the bismuth film deposition on GC and the electroanalytical parameters for cadmium (Cd²⁺) determination using differential pulse anodic stripping voltammetry (DPASV). The influence of [Bi³⁺], deposition potential (Edeposition), and deposition time (tdeposition) on the bismuth film was evaluated, along with pulse amplitude (Epulse) and pulse duration (tpulse) for the electroanalytical parameters. The optimized parameters were [Bi³⁺] = 5 mg/L, Edeposition = -1100 mV, tdeposition = 650 s, Epulse = 160 mV, and tpulse = 20 ms. Under the optimal parameter combination, a calibration curve was constructed in a concentration range of 0.05 to 0.4 mg/L, achieving a limit of detection (LOD) and limit of quantification (LOQ) of 0.032 mg/L and 0.099 mg/L, respectively. The proposed analytical procedure was applied for Cd²⁺ quantification in cocoa seed samples from the Caquetá and Santander departments and was validated through atomic absorption spectroscopy (AAS), yielding satisfactory results.