Hach DR/850, Procedures Manual, Page: 316 / 460

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5.
Using an automatic
dispenser or TenSette
Pipet, add 1.0 mL of
concentrated sulfuric
acid to the mixing cell.
Note: Mixing concentrated
sulfuric acid and water is
not additive. Adding 1.0 mL
of concentrated sulfuric
acid to 9.0 mL of sample
does not result in a final
volume of 10.0 mL. This
factor is built into the
calibration curve.
6.
Cap the cell tightly
and invert it several
times. The solution will
become hot. Cool to
room temperature before
proceeding.
Note: Acidified samples
are stable for several
months when refrigerated
at 4 °C.
7.
Prepare a blank (see
note) by repeating Steps
4-6, substituting 9.0 mL
of deionized water for
the sample.
Note: The reagent blank is
stable and can be reused.
Verify reagent blank quality
by measuring the
absorbance of the blank vs.
a clean COD vial filled
with deionized water. The
absorbance range, when
using chloride removal,
should be about
1.31-1.36.
Note: Use a clean pipet or
rinse it thoroughly.
Note: One blank must be
run with each lot of
reagents. Run all samples
and blanks with the same
lot of vials (lot number is
on the container label).
8.
If not already on,
turn on the DRB 200
Reactor and heat to
150 °C.
Note: See DRB 200 user
manual for selecting pre-
programmed temperature
applications.
PREPARE BLANK
OXYGEN DEMAND, CHEMICAL,
continued