YSI 910 COD Colorimeter - Manual (Page 4)

4
General notes
• Prior to measurement ensure that the sample is suitable for analysis (no major interference) and
does not require any preparation i.e. pH adjustment, filtration etc.
• Reagents are designed for use in chemical analysis only and should be kept well out of the reach
of children.
• Ensure proper disposal of reagent solutions.
• Material Safety Data Sheets: available on request.
Chemical Method notes:
Method:
the sample is heated at 150
o
C for two hours in the presence of potassium dichromate, which is a
strong oxidizing agent. Organic compounds in the sample are oxidized, reducing the dichromate ion
(Cr
2
O
7
2– ) to the green chromic ion (Cr 3+ ).
In the Low Range (LR) Test (0-150 mg/L), the amount of remaining Cr
6+ is measured; In the
Mid Range (MR) (0-1,500 mg/L) or (HR) (0-15,000 mg/L), the amount of Cr
3+ produced is
measured. The results are measured as the amount of oxygen (O
2
) consumed per liter of
water sample. the lr and Mr test is displayed in mg/l while the Hr test shows g/l.
The COD reagent contains both mercury and silver—the mercury controls chloride
interferences and the silver functions as a catalyst to speed the reaction.
application:
Samples can be measured if the chloride content does not exceed 1,000 mg/l (LR/MR) or 10,000 mg/l
(Hr).
In exceptional cases, compounds contained in the water cannot be adequately oxidized. This results
in low reading, compared with the reference method.
Different methods of sampling, preparation of the sample itself and the time elapsed between taking
the sample and analysis can all affect the obtained results.
General notes