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 cetylpyridinium (CP+) and 2,4,6‐trinitrobenzenesulfonate (TNBS−) as the electroactive species was developed. The electrode exhibits a rapid and Nernstian response to TNBS− from 5.0 × 10−5 to 1.0 × 10−2M at 25 ± 0.1°C. The response is unaffected by the change of pH over the range 2–12. Selectivity coefficients for a larger number of organic and inorganic anions and sugars are given. The electrode has been successfully applied to the determination of L‐dopa, carbidopa, methyldopa and aspartame in pure solutions and in their pharmaceutical formulations with a precision and accuracy of 0.9–1.3% without interference from excipients.