Folic acid Determination in neutral pH electrolyte by Adsorptive Stripping Voltammetry at the Mercury Film Electrode

A stripping method for the determination of folic acid at the submicromolar concentration levels is described. The method is based on controlled adsorptive accumulation of folic acid at the hanging mercury drop electrode followed by differential pulse measurement of the adsorbate. The adsorptive stripping response was evaluated with respect to concentration dependence, accumulation time, accumulation potential, scan-rate, size of the mercury drop, pH, ionic strength, presence of possible interferences and other variables. Cyclic voltammograms at pH 7.1(0.2 mol.L -1 KH2PO4/ NaOH buffer solution) showed four cathodic peaks at 0.57, 0.75, -1.18 and -1.39 V. The second peak, (at –0.75 mV), was the most useful for analytical purposes (more sensitive, quasi reversible and well defined) and it was used for quantifying folic acid by differential pulse adsorptive stripping voltammetry in four types of pharmaceutical multivitamin preparations. Sequential determination of folic acid with ascorbic acid is also possible. The results obtained in analysing medicines having folic acid as active constituent were compared favourably with those obtained by HPLC with UV detection. The average content of folic acid found in these medicines by HPLC was 4.81±0.09mg and by voltammetry, 4.87±0.09mg. The proposed method is very simple, efficient and does not involve time-consuming separation steps. KeywordsAscorbic acid, differential pulse voltammetry, folic acid, pharmaceutical preparations, vitamins.