Hach DR/700 Procedures Manual page 442

PHOSPHORUS, TOTAL,
30 minutes
4.
Place the flask 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 deeper than the
solution level in the
flask, Continue boiling
for 30 minutes.
continued
5.
Cool the sample
to room temperature.
52-116
6.
Add 2.0 mL of
5.0 N Sodium
Hydroxide Solution.
Swirl to mix.
Note: Use the 1-mL
calibrated dropper
provided.