Time-biased square wave differential electrolytic potentiometry for determination of ascorbic acid in a complex matrix at multi-walled carbon nanotubes modified silver electrodes

Carbon nanotubes modified silver electrodes (CNTs/Ag) have been prepared by the catalytic thermal decomposition of ethylene in a chemical vapor deposition reactor. CNTs growth parameters such as ratio of ethylene to hydrogen, temperature and time were optimized, to enhance the electrode functionality for application. The electrode surface was characterized by scanning electron microscopy, transition electron microscopy and Raman spectroscopy. The optimum ethylene to hydrogen (C₂H₂:H₂) ratio, temperature and time were found to be 75:90 sccm, 800 °C, and 20 min respectively. The CNTs/Ag electrodes prepared by this method exhibited well adhesion of the CNTs to the metal surface enabling their use for multiple times. The CNTs/Ag electrodes were successfully applied as indicating system in biased square wave differential electrolytic potentiometry (DEP) for the determination of ascorbic acid in a drug formulation and complex Baobab fruit matrix. CNTs/Ag electrodes showed high performance and durability, and the biased square wave led to enhanced DEP signal and lowered the detection limit for ascorbic acid to less than 25 µM. These promising results open the way for the use of CNTs/Ag electrodes as indicating setup for automated flowing systems like flow injection analysis.