A new ternary deep eutectic solvent for electropolymerization of thionine on glassy carbon electrodes modified with multiwalled carbon nanotubes for the determination of ascorbic acid

The phenazine redox dye, thionine (Th), was used to prepare poly(thionine) (PTh) polymer film modified electrodes. PTh was electrodeposited on glassy carbon electrodes (GCE) and on GCE modified with multiwalled carbon nanotubes (MWCNT) by potential cycling electropolymerization in the ternary deep eutectic solvent composed of choline chloride (ChCl), thymol (Thy), ethylene glycol (EG), ChCl-Thy-EG (1:1:4) with the addition of different doping acids. The MWCNT promote greater polymer growth, conductivity and increased stability of the polymer films. The modified electrodes, PTh/MWCNT/GCE, were characterized by cyclic voltammetry, electrochemical impedance spectroscopy and the morphology of its surface by scanning electron microscopy. PTh/MWCNT/GCE was used in the determination of ascorbic acid (AA) using fixed potential amperometry with a linear range of 2.5 μM-100 μM and a detection limit of 0.68 μM. The proposed sensor was tested on commercial pharmaceutical samples successfully with good sensitivity, repeatability and reproducibility.