61-69
OXYGEN DEMAND, CHEMICAL, continued
7. Prepare a blank
by repeating Steps 3
to 6, substituting 2.00
mL (0.2 mL for 0 to
15,000 mg/L range)
demineralized water
for the sample.
Note: Be sure the pipet
is well rinsed or use a
clean pipet.
Note: One blank must
be run with each set of
samples. All tests
(samples and blanks)
should be run with the
same lot of vials. The
lot number appears on
the container label.
8. Heat the vials for
2 hours.
Note: Many wastewater
samples contain easily
digested materials that
are digested in less than
2 hours. If desired,
measure the
concentration (while still
hot) at 15-minute
intervals until it remains
unchanged. At this point,
the sample is completely
digested. Cool vials to
room temperature for
final measurement.
9. Turn the reactor
off. Wait 20 minutes
for the vials to cool to
120
o
C or less.
2 hours
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