Curcumin Electroanalysis at a Disposable Graphite Electrode

Curcumin (CU, turmeric), a polyphenolic phytochemical that is largely used as a food spice, has benefits for human health, which have led to increased interest in its therapeutic applications and its analysis from different matrices. The two guaiacol moieties of CU are responsible for its antioxidant properties and allow for its voltammetric quantification. Cyclic and differential pulse voltammetry (DPV) investigations at a single-use pencil graphite electrode (PGE) emphasized complex pH-dependent electrode processes, involving an equal number of protons and electrons. Theoretical calculations predicted a folded geometry for the β-diketone CU conformers, which interact with the PGE surface, exposing the electroactive moieties of only one aromatic ring. The Gibbs energy variations of the structures involved in CU electro-oxidation and the theoretical electrochemical potential values were calculated. CU's DPV cathodic peak intensity recorded at an HB-type PGE in 0.05 mol × L^-1 H₂SO₄ varied linearly in the range 5.00 × 10^-8-5.00 × 10^-6 mol × L^-1 CU. The method's detection and quantification limits were 2.12 × 10^-8 mol × L^-1 and 6.42 × 10^-8 mol × L^-1, respectively. The practical applicability of the developed method, successfully tested by CU assessment in dietary supplements, provided a recovery of 99.28 ± 2.04%.