Hach DR/700 Procedures Manual page 722

PHOSPHORUS, REACTIVE,
4.
Fill a 10-mL cell
to the 10-mL line
with sample.
Note: For proof of
accuracy, use a 1.0 mg/L
Phosphate (0.33 mg/L P)
Standard Solution (listed
under Optional
Reagents) following
these steps, in place of
the sample.
Note: Run a reagent
blank for this test. Use
demineralized water in
place of the sample in
Step 4. Subtract this
result from all test results
run with this lot of
PhosVer.
Note: Optional 25-mL
reagents sample may be
used (see Optional
Reagents).
5.
Add the contents
of one PhosVer 3
Phosphate Powder
Pillow to the sample
cell (the prepared
sample). Cap and
invert several times to
mix.
Note: A blue color will
form if phosphate is
present.
81-48
continued
2 minutes
6.
Wait two minutes.
Note: An 8-10 minute
reaction period should
be used if determining
total phosphate
following the acid-
persulfate digestion.
Note: If the sample
temperature is less than
°
15 C (59 °F), allow 9
minutes of reaction
time.