ALTERNATING-CURRENT ADSORPTIVE STRIPPING VOLTAMMETRY IN A FLOW SYSTEM FOR THE DETERMINATION OF ULTRATRACE AMOUNTS OF FOLIC-ACID

The adsorptive behaviour of folic acid on the surface of a mercury electrode was investigated and the surface rate constant of electrochemical reaction was determined (k(s) = 440 s-1, 25-degrees-C). Adsorptive stripping voltammetry was applied to a flow system for the determination of ultratrace amounts of folic acid. The effects of various parameters, for e.g., flow-rate, flow time of solution and accumulation potential, on peak currents are discussed. Interferences from the test solution can be eliminated by the technique of medium exchange. The peak current is proportional to the concentration of folic acid in the range of 10(-8)-10(-11) mol l-1 with a correlation coefficient of 0.998. The relative standard deviation is 2.5% at a concentration of 2.8 x 10(-8) mol l-1 (7 determinations). The detection limit of a.c. adsorptive stripping voltammetry is as low as 2 x 10(-12) mol l-1 (10-min accumulation).