In line measurement of chemical oxygen demand by means of multipulse amperometry at a rotating Pt ring -: Pt/PbO2 disc electrode

In this paper an amperometric method that makes use of a the rotating ring-disc electrode (RRDE) configuration is described for the determination of the chemical oxygen demand (COD). It is shown that the strong oxidant necessary in COD measurements can be generated by an electrolytic in situ formation of an aggressive species, at the disc part of the ring-disc electrode, that oxidises the compounds that contribute to the GOD. The excess of aggressive species formed reacts further to oxygen, which is determined at the ring electrode. Compensation of the disc current signal for the ring current signal finally results into the COD value of the solution. In this paper the COD value of real samples from a textile and a photo developing company were analysed and it was shown that a precision of 1% could be obtained within the range of 20-25,000 mg l(-1). An important advantage is the fact that the COD value of a solution of unknown composition can be obtained within 1 min after calibration of the electrode system. (C) 2001 Elsevier Science B.V. All rights reserved.