The determination of chemical oxygen demand in spent caustic waste by closed-tube digestion procedure using potentiometric determination

Measurement of the COD of a spent caustic solution involves firstly digestion of a test sample with dichromate solution and secondly measurementof dichromate remained by titration by ferrous ammonium sulfate (FAS) to an end point. In this paper we study by a potentiometric end point withAg/AgCl reference electrode and gold rode electrode. The potentiometric end point is sharp and easily identified especially for the samples with highturbidity and color that other methods such as colorimetric in this type of sample do not result in high precision. Because interim of titration respondsquickly to potential changes within the (Cr+6/Cr+3 & Fe+2/Fe+3) solution producing stable readings that is lead to accurate COD measurement. Finally resultsare compared with data determined using colorimetric method for standard samples. It is shown that the potentiometric end point titration with gold rode electrode can be used with equal or better facility.