Construction of a Triphenyltetrazolium Liquid Membrane Ion Selective Electrode and its Analytical Application to the Assay of Vitamin C

 The construction of a liquid triphenyltetrazolium cation (TT+) ion-selective electrode (ISE) based on [TT+]3[P(W3O10)4] salt dissolved in 2-nitrotoluene is described. The liquid membrane electrode exhibits a rapid and almost Nernstian response to triphenyltetrazolium cations in the concentration range from 2×10−4 to 1×10−2 mol l−1. The Nernstian slope is 56–58 mV decade−1 which remains constant for at least two months. The response is virtually unaffected by pH changes in the range 3–12. Major interferents are periodate and malate. Deviation from linearity is also observed in the presence of bromide, iodide and thiocyanate, due to their precipitation with triphenyltetrazolium cations. Analytical applications such as direct potentiometry for the determination of TT+ in aqueous solutions and indirect potentiometry for the assay of ascorbic acid (vitamin C) in pharmaceutical preparations are described. Ascorbic acid in the range of 150–500 mg l−1, under specified experimental conditions, can be determined with mean relative error of 1.9%.