Determination of chlorine and dissolved oxygen in waters and of ascorbic acid in pharmaceuticals by iodimetric potentiometric titration using a plasticized poly(vinyl chloride) membrane electrode

The response to triiodide of an electrode based on a membrane containing poly(vinyl chloride) and 2-nitrophenyl octyl ether as plasticizer in a 1:2 (ww) ratio is studied. The electrode is suitable for the automatic potentiometric titration of triiodide in the concentration range 10−5–10−3 mol l−1 with thiosulphate. The electrode has been satisfactorily applied to the determination of chlorine and dissolved oxygen in tap waters and that of ascorbic acid in pharmaceuticals. Possible explanations for the response of the membrane to triiodide are included.