RESUMO
Objective To estimate the marginal value of the chemical oxygen demand (COD) in drinking water by evaluation of uncertainty. Methods According to Evaluation and Expression of Uncertainty in Measurement (JJF1059-1999), analysis of measure uncertainty of the chemical oxygen demand determined by acidic potassium permanganate titrate prescribed in Sanitary Standards for Drinking Water (2001) was conducted. Results The type A relative standard uncertainty was 0.584%, type B was 0.781%, in which the sub-item uncertainty led by using 25 ml burette was 0.708%, the water sample volume was 0.056%, the adjusted potassium permanganate standard solution was 0.325%; the relative combined standard uncertainty was 0.975%, the expanded uncertainty was 1.95%. Conclusion According to the result of the uncertainty (3.08?0.06) mg/L, COD in the polluted sample exceeds the limit, the use of 25 ml burette produced the most contribution to the uncertainty.