Differential-pulse cathodic stripping voltammetric determination of nedocromil sodium at an unmodified and at a poly-L-lysine modified hanging mercury drop electrode

Abstract

Differential-pulse cathodic stripping voltammetry was used to determine nedocromil sodium in the range 5 × 10^–9–1.0 × 10^–7 mol dm^–3 at a hanging mercury drop electrode in 0.1 mol dm^–3 hydrochloric acid solution. Three independent irreversible reduction peaks (at –0.48, –0.57 and –0.92 V) were obtained: nedocromil can be accumulated itself or as either of its first two reduction products and then determined cathodically. The highest sensitivity was obtained using the third reduction peak after accumulation at –0.8 V: the detection limit was calculated to be 5 × 10^–9 mol dm^–3 for 1 min accumulation. The effect of modifying the electrode with adsorbed poly-L-lysine was not significant: the heights of the peaks were often suppressed slightly. However, the height of the third peak at pH 4, which was considerably lower than that at pH 1, was restored to a comparable height when the electrode was so modified.