Hach DR/700 - Page 434

52-108
PHOSPHORUS REACTIVE, continued
4. Fill a 25-mL
graduate mixing
cylinder with 25 mL
of sample.
Note: For proof of
accuracy, use a
10.0 mg/L as PO
4
3-
(3.3 mg/L as P)
phosphorus standard
solution (preparation
given in Accuracy Check)
in place of the sample.
Note: Run a reagent
blank with each lot of
reagent. Repeat the test
using demineralized
water as the sample.
Subtract this value from
each result obtained with
this lot of reagent.
5. Add 1 mL of
Molybdate Reagent
using a 1-mL
calibrated dropper.
6. Add 1 mL of
Amino Acid Reagent
Solution. Stopper
and invert several
times to mix (the
prepared sample).
Note: A blue color will
form if phosphate is
present.
Note: Substitute the
contents of one Amino
Acid Reagent Powder
Pillow for 1 mL of
Amino Acid Reagent
Solution if desired.
7. Wait 10 minutes. 8. During the 10-
minute period, fill a
10-mL cell to the
10-mL line with
sample (the blank).
Cap.
9. Place the blank in
the cell holder.
Note: In bright sunlight,
it may be necessary to
close the cell
compartment cover.
10 minutes