Determination of low chemical oxygen demand using potentiometry and a modified Gran function

The paper presents development and application of a method for determining chemical oxygen demand (COD) in aqueous solutions down to a concentration of 3 mg COD/l (+1 mg/l). The method hinges on the utilisation of a modified Gran function coupled with a potentiometric titration of digested test solutions with ferrous ammonium sulfate (FAS) titrant. Verification is presented using samples of known COD and composition (glucose), and unknown COD and composition, tap water (and dilutions of this) originating from Lake Kinneret (Sea of Galilee), and tertiary effluents from a wetland pilot plant. The latter are compared with measurements of organic concentrations obtained using an organic carbon analyser.