DIFFERENTIAL-PULSE ADSORPTIVE STRIPPING VOLTAMMETRIC DETERMINATION OF SODIUM CROMOGLYCATE AT A HANGING MERCURY DROP ELECTRODE

Sodium cromoglycate is strongly adsorbed onto mercury, and can be determined readily at the 1 x 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 x 10(-7) and 1 x 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 X 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 X 10(-6) mol dm-3 levels of several heavy metal ions. Human serum albumin at the 1.6 X 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.