Application of nafion-coated mercury film electrodes to the microdetermination of formaldehyde by differential-pulse voltammetry

Formaldehyde, after in situ conversion to an ionic derivative with Girard's reagent T, was first accumulated on a Nafion-coated mercury film electrode. The adsorbed derivative was then determined in aqueous solution using differential-pulse voltammetry. A single peak centred at -1.24 V (versus Ag-AgCl) was observed at pH 9.7 when using 0.4 mol l(-1) NH4Cl-NH3 as the supporting electrolyte. The calibration graphs were rectilinear over the range from 2.0 x 10(-7) td 1.0 x 10(-5) mol l(-1) formaldehyde. By incorporating a preconcentration step via the Nafion-modified electrode, the detection limit of the method for formaldehyde was calculated to be 3.4 x 10(-8) mol l(-1). The reproducibility and lifetime studies of the electrodes indicated that a newly prepared electrode could be repeatedly used for more than ten measurements with satisfactory precision, In addition, the method can be extended, without any modification, to the determination of acetaldehyde.