Chemical oxygen demand (COD) is one of the most relevant chemical parameters for the management of
wastewater treatment facilities including the control of the quality of an effluent. The adequacy of decisions
based on COD values relies on the quality of the measurements. Cost effective management of the
minor sources of uncertainty can be applied to the analytical procedure without affecting measurement
quality. This work presents a detailed assessment of the determination of COD values in wastewaters,
according to ISO6060:1989 standard, which can support reduction of both measurement uncertainty and
cost of analysis. This assessment includes the definition of the measurement traceability chain and the
validation of the measurement procedure supported on sound and objective criteria. Detailed models of
the measurement performance, including uncertainty, developed from the Differential Approach, were
successfully validated by proficiency tests. The assumption of the measurement function linearity of the
uncertainty propagation law was tested through the comparison with the numerical Kragten method.
The gathered information supported the definition of strategies for measurement uncertainty or cost
reduction. The developed models are available as electronic supplementary material, in an MS-Excel file,
to be updated with the user’s data.