Electrochemical sensing of Ni2+ on Screen-Printed Carbon Electrodes (SPCEs) by exploiting the chelating and sequestering abilities of the natural polyphenolic compound morin

The research aimed to develop an alternative strategy for the selective detection of Ni²⁺ in aqueous solution, exploring the chelating and sequestering properties of a natural polyphenolic ligand, morin (MRN, L⁵⁻). To this end, the formation constant values of Ni²⁺-MRN species (in NaCl aqueous solutions, at I/mol L⁻¹ = 0.15 and T/K = 298.15) were determined to evaluate the sequestering abilities of MRN toward Ni²⁺ under different pH conditions (2.0 ≤ pH ≤ 9.0). In this pH range, Cyclic Voltammetry (CV) experiments were conducted on MRN, without and in the presence of Ni²⁺. In both cases, the peak anodic current (i_pa) of MRN was higher at pH 7.3. Therefore, the binding ability of the ligand was exploited to electrochemically detect Ni²⁺ by performing titrations of MRN solutions with Ni²⁺ in Britton-Robinson (BR) buffer (pH 7.3) using Different Pulse Voltammetry (DPV). The linear concentration range was found to be: 0.5 ≤ [Ni²⁺]/nmol L⁻¹ ≤ 9.3, with Limit of Detection (LOD) and Limit of Quantification (LOQ) values of 0.21 nmol L⁻¹ and 0.71 nmol L⁻¹, respectively. The stability, repeatability, reproducibility and selectivity of the system Ni²⁺-MRN were also defined. For the study of selectivity, Ca²⁺, Mg²⁺, Mn²⁺, Fe²⁺, Co²⁺, Cu²⁺ and Zn²⁺, up to a 100-fold concentration, were taken into account.