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 (ipa) 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.