Utility of iodine and 7,7,8,8-tetracyanoquinodimethane for determination of terfenadine

Simple and sensitive spectrophotometric methods for the assay of terfenadine are described. The first is based on the reaction of terfenadine with iodine to give a molecular charge-transfer complex, the terfenadine acting as an n-electron donor and iodine as a sigma-electron acceptor. The second depends on the formation of a highly coloured stable radical anion between terfenadine and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as a pi-electron acceptor. Beer's law is obeyed over the terfenadine concentration range 0.2-1.2 mg/100 ml. The proposed methods have been successfully applied to the analysis of commercial terfenadine tablets.