Hach DR/700 Procedures Manual page 484

IRON,
continued
4.
Fill a 25-mL cell
to the 25-mL line
with sample.
Note: Rinse glassware
with a 1:1 hydrochloric
acid solution. Rinse
again with
demineralized water.
These two steps will
remove iron deposits
which can cause slightly
higher results.
Note: For proof of
accuracy, use a 0.4 mg/L
iron standard solution
(preparation given in the
Accuracy Check) in
place of the sample.
5.
Add the contents
of one FerroZine Iron
Reagent Solution
Pillow to the cell (the
prepared sample).
Cap and invert several
times to mix.
Note: Do not allow the
clippers to come into
contact with the
contents of the pillow.
Note: 0.5 mL of
FerroZine Iron Reagent
Solution can be used in
place of the solution
pillow if preferred.
Note: If the sample
contains rust, see
Interferences, below.
55-36
5 minutes
6.
Wait 5 minutes.
Note: A violet color will
develop if iron is
present.