oa South African Journal of Chemistry - Determination of sulphate by flow-injection analysis using a coated tubular solid-state lead ion-selective electrode



A flow-injection analysis system is descriptionbed for the indirect determination of sulphate by direct measurement of lead with a coated tubular lead ion-selective electrode. An excess of lead(II) ions as lead perchlorate is added to the sample solution-carrier stream mixture as a reagent stream in an environment of sodium perchlorate, as ionic strength adjustor, and methanol-formaldehyde, to decrease solubility of formed PbSO4 and retard oxidation of the membrane. The system is useful for the determination of sulphate in the range 50-10 000 mg dm-3 at a sampling rate of 60 h-1 with a coefficient of variation of better than 1,70%. Major interference is caused by cations (Ag+, Hg2+, Cu2+) and anions (Po43-) which form insoluble lead salts.


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