Hach DR2400 - Page 550

Oxygen Demand, Chemical
Oxygen Demand, Chemical
Page 6 of 8
OxygenCOD_None_Mid_RCD_Eng_Ody.fm
Method Performance
Precision
Standard: 80 mg/L COD (Low Range), 800 mg/L COD (High Range), and
10,000mg/L COD (High Range Plus)
See Section 3.4.3 Precision on page 44 for more information, or if the standard
concentration did not fall within the specified range.
Sensitivity
See Section 3.4.5 Sensitivity on page 44 for more information.
Alternate Reagents
Mercury-free COD2 Reagents can provide a mercury-free testing option for non-
reporting purposes. For process control applications, COD2 Reagents will
eliminate mercury waste and save on disposal costs. These reagents are fully
compatible with test procedures and calibration curves programmed into the
DR/2400 spectrophotometer. Determine chloride and ammonia for accurate
results.
Note: These reagents are not approved for USEPA reporting purposes. Request a copy of the
COD Reagent Vial Information Brochure, Lit. No. 1356, for more information about specific
applications.
Summary of Method
The mg/L COD results are defined as the mg of O
2
consumed per liter of sample
under conditions of this procedure. In this procedure, the sample is heated for
two hours with a strong oxidizing agent, potassium dichromate. Oxidizable
organic compounds react, reducing the dichromate ion (Cr
2
O
7
2–
) to green
chromic ion (Cr
3+
). When the 3–150 mg/L colorimetric or titrimetric method is
used, the amount of Cr
6+
remaining is determined. When the 20–1,500 mg/L or
200–15,000 mg/L colorimetric method is used, the amount of Cr
3+
produced is
determined. The COD reagent also contains silver and mercury ions. Silver is a
catalyst, and mercury is used to complex chloride interferences. Test results for
the 3 to 150 mg/L range are measured at 420 nm. Test results for the 20 to 1,500
and the 2000 to 15,000 mg/L COD range are measured at 620 nm.
Program Range (mg/L) 95% Confidence Limits of Distribution
430 3–150 77.6–82.4 mg/L COD
435 20–1500 778–822 mg/L COD
435 200–15000 9778–10,222 mg/L COD
Program Portion of Curve ∆Abs ∆Concentration
430 Entire range 0.010 3 mg/L COD
435 Entire range 0.010 20 mg/L COD