a small sample size and produces minimal waste. A 2 mL aliquot is added todichromate solution and
allowed to digest at 150 °C for 2 hours. Concentration (mg COD/L) is determined by measuring the
increase in absorbance at 606 nm, the absorbance peak for the chromic ion, or determining excess
dichromate by measuring the absorbance at 440 nm [38,39].
High range COD digestion vials from the Hach Company (Loveland, CO, USA) were used to digest
samples produced during unrelated research activities conducted to develop precision and bias
statements for a newly developed analytical procedure. 147 vials were digested and used to conduct
this comparison. Digestion was performed with a Hach DRB200 and absorbance was determined by
both the OS colorimeter and a commercial Hach DR890 portable colorimeter.Absorbance units were
recorded from both units sequentially with five replicate readings from each.