Differential-pulse adsorptive stripping voltammetric determination of sodium cromoglycate at a hanging mercury drop electrode

Abstract

Sodium cromoglycate is strongly adsorbed onto mercury, and can be determined readily at the 1 × 10–10 mol dm–3 level, after adsorption onto a hanging mercury drop electrode from pH 4.5 acetate buffer solution. The adsorbed cromoglycate anion was reduced at –0.87 V versus Ag—AgCl, after accumulation at –0.6 V. Slightly higher signals can be obtained by accumulating at potentials more positive than the potential of zero charge (–0.5 V). Accumulation at –0.6 V, however, eliminates interference from more easily reduced adsorbates, and the analysis time is decreased. At the 0.5 × 10–7 and 1 × 10 –7 mol dm–3 levels, peak height increased rectilinearly with accumulation time up to 5 and 3 min, respectively, and peaks of useful size were observed at accumulation times as short as 15 s. Relative standard deviations at the 1 × 10–7 mol dm–3 level were typically <4%(five determinations). No significant interference was observed at this level from 1 mg dm–3 levels of several surfactants and 1 × 10–6 mol dm–3 levels of several heavy metal ions. Human serum albumin at the 1.6 × 10–7 mol dm–3 level caused the height of the peak to be reduced to 25% of its original size. The method was tested satisfactorily by analysing four formulation solutions of the drug.