Hach DR/700 Procedures Manual page 141

PHOSPHORUS, ACID HYDROLYZABLE
For water, wastewater, seawater
Hydrolysis to Orthophosphate Method*
1.
Measure 25 mL of
sample into a 50-mL
erlenmeyer flask
using a graduated
cylinder.
Note: Wash all
glassware with
hydrochloric acid, 6 N.
Rinse with
demineralized water.
Note: If prompt analysis
is impossible, see
Sampling and Storage
following these steps.
*Adapted from Standard Methods for the Examination of Water and Wastewater
2.
Add 2.0 mL of
Sulfuric Acid
Solution, 5.25 N.
Note: Use the 1-mL
calibrated dropper
provided.
42-57
Method 8180
30 minutes
3.
Place the flask
(the prepared sample)
on a hot plate. Boil
gently for 30 minutes.
Note: Maintain the
volume near 20 mL by
adding small amounts of
demineralized water.
Do not exceed 20 mL.
Note: This is more
easily accomplished
with a "double-boiler"
technique. Place the
flask in a pan or beaker
of boiling water which
is just deeper than the
solution level in the
flask. Continue boiling
for 30 minutes.