Hach DR/700 Procedures Manual page 479

DEHA,
continued
7.
Add exactly
0.5 mL of DEHA
Reagent 2 Solution to
each sample cell.
Cap and invert several
times to mix.
Immediately place
the sample cells in the
dark.
Note: A purple color
will slowly develop if
DEHA is present.
10 minutes
8.
Immediately
begin timing a
10-minute period.
Note: Temperature and
reaction time affect the
results. Be sure these
factors are controlled as
described.
Note: The sample cells
must remain in the dark
for the entire 10-minute
period.
55-31
9.
After the
10-minute period,
place the blank in the
cell holder.
Note: Typical indoor
lighting permits the
DR/700 to operate with
the cell compartment
open. In bright
sunlight, it may be
necessary to close the
cell compartment cover.
Transfer 10 mL of the
blank and 10 mL of the
sample to a
10-mL sample cell and
proceed.