The pretreament selected as optimal was a potential cycle from 0 to 2 V at a frequency of 10 Hz for a period of 1 min in pH 2 BR buffer. When 10 consecutive voltammograms were obtained for folic acid without intermediate electrochemical
pretreatment, the current response decreased with each successive scan. Using the optimal pretreatment between each DPV scan, the response was constant, with the precision calculated as the relative standard deviation (n = 10) being better than
2.5%.