YSI 910 COD Colorimeter - Manual (Page 6)

6
Methods
COD reagents
Select the appropriate vial for the desired range*:
LR-Range:
0 – 150 mg/l, part number 251990Y, 25 count
MR-Range: 0 – 1500 mg/l, part number 251991Y, 25 count
HR-Range: 0 – 15000 mg/l, part number 251992Y, 25 count
*Reagents are also availble in 150 count packages.
preparing the sample
Open a reaction vial with a white cap and add the specified volume.
(Ensure that appropriate personnel safety equipment is used.)
lr-/Mr: 2 ml water sample
Hr: 0.2 ml water sample
Prepare a blank (Note 1) by using deionized water (TOC-free) instead of the sample
(lr/Mr: 2 ml, Hr: 0.2 ml).
Replace the cap tightly. Invert the vial gently several times to mix the contents (The vial will become
hot during mixing!) and digest the vials for 120 minutes in the reactor at a temperature of 150°C.
Remove the vials from the reactor and allow them to cool down to 60°C or less. Mix the contents by
inverting each vial several times while still warm. Then allow the vials to cool to ambient temperature
before measuring.
Guidelines for photometric measurements
1.
Run samples and blanks with the same batch of vials.
The blank is stable when stored in the dark and can be used for further measurements with vials
from the same batch.
2.
Don‘t place hot vials in the adapter. Allow the vials to cool to room temperature for
a minimum 45 minutes. It is recommended to leave the vials to cool over night.
3. suspended solids in the vial lead to incorrect measurements. For this reason it is important to place
the vials carefully in the adapter. The precipitant at the bottom of the sample should not be
suspended.
4.
Clean the outside of the vials with a towel to remove fingerprints or other marks.
5.
Avoid spillage of water or reagent solution into the sample chamber because this can lead to incor-
rect test results.
6.
Contamination of the transparent cell chamber can result in incorrect readings. Check at regular in-
tervals and – if necessary – clean the transparent cell chamber using a moist cloth or cotton swab.
7.
Large temperature differences between the instrument and the environment can lead to errors –
e.g. due to the formation of condensation in the cell chamber or on the vial.
8.
To avoid errors caused by stray light do not use the instrument in bright sunlight.