DIFFERENTIAL-PULSE CATHODIC STRIPPING VOLTAMMETRIC DETERMINATION OF NEDOCROMIL SODIUM AT AN UNMODIFIED AND AT A POLY-L-LYSINE MODIFIED HANGING MERCURY DROP ELECTRODE

Differential-pulse cathodic stripping voltammetry was used to determin e nedocromil sodium in the range 5 x 10(-9)-1.0 x 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 o r as either of its first tao reduction products and then determined ca thodically. The highest sensitivity was obtained using the third reduc tion peak after accumulation at -0.8 V: the detection limit was calcul ated to be 5 x 10(-9) mol dm(-3) for 1 min accumulation. The effect of modifying the electrode with adsorbed poly-L-IS sine was not signific ant: the heights of the peaks were often suppressed slightly. However, the height of the third peak at pH 4, which was considerably lower th an that at pH 1, was restored to a comparable height when the electrod e was so modified.