Chemical oxygen demand with APHA/AWWA/WEF 5220 D procedure for high concentration adapted to micro-volume

Abstract

In this study, linearity and precision tests were performed for the determination of the chemical oxygen demand (COD) in water, for a micro-volume adaptation of the closed reflux method for small volume for high range of APHA/AWWA/WEF. The main objective of the work was to demonstrate that it is possible to obtain adequate measurements by adapting the APHA/AWWA/WEF method 5220 D, a widely used international reference for determining COD in water, on a micro-volume adaptation. The micro-volume adapted method required only changes in the concentration of each substance in the digestion solution, but not in the silver sulfate catalyst solution, so that the concentration of each of these substances in the tubes digestion was almost equal to that corresponding to the original method (except for mercury sulfate, which was deliberately reduced). In the micro-volume adaptation presented here, the dosed volumes of all liquid reagents were measured using class A volumetric pipettes, improving the precision of measurements with respect to the use of both graduated and plunger pipettes (necessary to carry out the original method). The results obtained for the micro-volume adaptation demonstrated excellent linear fitting and precision of the system.