POTENTIOMETRIC DETERMINATION OF L-DOPA, CARBIDOPA, METHYLDOPA AND ASPARTAME USING A NEW TRINITROBENZENESULFONATE SELECTIVE ELECTRODE

A selective PVC membrane electrode based on the ion-pair of cetylpyrid inium (CP+) and 2,4,6-trinitrobenzenesulfonate (TNBS-) as the electroa ctive species was developed. The electrode exhibits a rapid and Nernst ian response to TNBS- from 5.0 x 10(-5) to 1.0 x 10(-2) M at 25 +/- 0. 1 degrees C. The response is unaffected by the change of pH over the r ange 2-12. Selectivity coefficients for a larger number of organic and inorganic anions and sugars are given. The electrode has been success fully applied to the determination of L-dopa, carbidopa, methyldopa an d aspartame in pure solutions and in their pharmaceutical formulations with a precision and accuracy of 0.9-1.3% without interference from e xcipients.