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DIGESTION PROCEDURE FOR AQUEOUS LIQUIDS,
4:00
5.
Boil 4 more minutes.
Do not boil the sample
to dryness. If sulfuric
acid is not present in the
flask after the 4 minute
heating, do not proceed
with Step 6! Discard
sample if it evaporates to
dryness. Start over and
use a larger volume of
sulfuric acid in Step 2 of
this procedure. Or
choose a smaller sample
amount for digestion.
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6.
Do not proceed if
sulfuric acid is not
visible in the flask! Add
10 mL of 50% Hydrogen
Peroxide to the charred
sample via the funnel on
the fractionating column.
Note: Visually confirm the
presence of sulfuric acid in
the flask before adding
hydrogen peroxide.
Note: If the digest does not
turn colorless, add 5 mL
increments of hydrogen
peroxide until the digest
becomes clear or does not
change color.
Note: If sample foams
during peroxide addition,
remove the Digesdahl
digestion flask and
fractionating column (use
finger cots). Starting with
Step 1, repeat the digestion
adding only 2 mL of
hydrogen peroxide. Then
follow with 8 mL of
hydrogen peroxide.
Note: Do not heat
to dryness.
7.
After addition of
hydrogen peroxide is
complete, boil off excess
hydrogen peroxide by
heating for one more
minute. Do not heat
to dryness.
Note: If the sample goes
to dryness, turn off the
Digesdahl and air cool to
room temperature. Add
water to flask before
handling. Repeat the
digestion from the
beginning using a new
sample.
40
continued
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8.
Take the hot flask off
the heater and allow the
flask to cool. Remove
the fractionating column
from the digestion flask.
Note: Use finger cots to
remove the digestion flask.
Place it on a cooling pad
for at least one minute.
Then remove the column.
Do not add water to the
flask until it has cooled.
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