Electrocatalytic determination of vitamin C using calixarene modified carbon paste electrodes

Effect of in situ complexation of some ions with variable valencies, like Co(II), Ni(II), Mn(II), Cu(II) and Pb(II) on the the electrooxidation of Vitamin C (L-ascorbic acid) was studied by cyclic voltammetry using carbon paste electrodes modified with p-tert-butylcalix[4]arene and p-tert-butylcalix[6]arene in perchloric acid, acetic acid and ammonium acetate media. Pb(II) was found to bind strongly with p-tert-butylcalix[4]arene in acetate medium, resulting in its being retained at the electrode surface and catalyzing the oxidation of ascorbic acid. The overpotential was reduced by about 200 mV with an increase in the peak currents. Linearity was observed over the range of 0.07-400 ppm with a detection limit of 30 ppb by differential pulse voltammetry. Interferences of some common substances like sugars and amino acids were studied and the modified electrode was used for the determination of vitamin C in commercial samples.