Determination of folic acid by adsorptive stripping voltammetry at the static mercury drop electrode

Folic acid can be determined at nanomolar concentrations by controlled adsorptive accumulation of folic acid on a static mercury drop electrode held at ?0.3 V vs. Ag/AgCl followed by reduction of the surface species. In 0.1 M sulfuric acid, a cathodic scan gives peaks at ?0.47 v and ?0.75 V vs. Ag/Agcl; the latter peak provides greater sensitivity. Differential-pulse stripping is shown to be superior to normal-pulse and d.c. stripping. After a 5-min preconcentration, the detection limit is about 1 × 10^?10 M folic acid. The adsorptive stripping response is evaluated with respect to concentration dependence, preconcentration time and potential, solution acidity and the presence of gelatin and bromide. The relative standard deviation at the 5 × 10^?8 M level is 1.2%. This method is applied to the determination of folic acid in pharmaceutical tablets.