Flow injection amperometric determination of ascorbic acid and dopamine at a sessile mercury drop electrode without deoxygenation

Abstract

Ascorbic acid can be determined by flow injection amperometry at a sessile mercury drop electrode without the need to deoxygenate the eluent or sample. The determination is made at +0.19 V vs. S.C.E. in pH 5.5 acetate buffer. The size of the blank signal is equivalent to about 0.01 µg ml^–1 of ascorbic acid and the signal is rectilinear up to about 60 µg ml^–1. Chloride gives an oxidation signal at the mercury electrode but at a more positive potential and at the 1 µg ml^–1 level of ascorbic acid 1000 µg ml^–1 of chloride ion did not interfere. Hydrodynamic voltammograms of dopamine [2-(3,4-dihydroxyphenyl)ethylamine] show a plateau distinct from that of ascorbic acid and the mercury oxidation cut-off. Calibration graphs obtained at +0.26 V vs. S.C.E. for dopamine are rectilinear in the range 0.1–60 µg ml^–1. At +0.26 V chloride ion gives a signal approximately 1% of that of dopamine on a molar basis and interferes at higher ratios.