Hach Digesdahl 23130-20 - Page 40

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9.
Dilute the digest with
approximately 70 mL of
deionized water. If not
analyzing for aluminum,
nickel or iron, dilute to
the
100-mL mark with
deionized water; skip
Step 10 and proceed to
Step 11. If analyzing for
nickel, aluminum or
iron, go to Step 10.
Note: Add deionized
water slowly at first. Cool
the flask if necessary
for handling.
10. Turn the
temperature dial to a
heat setting of 204 ° C
(400°F). Add 150 mL of
water to a 400-mL
beaker. Place the beaker
on the heater. Place the
flask in the beaker and
boil for 15 minutes.
Air cool to room
temperature and dilute to
the 100-mL mark with
deionized water. Invert
several times to mix.
11. If the sample has
visible turbidity, filter
or wait until the
turbidity settles, and the
upper portion of the
sample is clear.
Filter as follows:
a)
Place a filter paper into
the filter holder with
wrinkled surface upward.
b) Place the filter holder
assembly in the filtering
flask and wet the filter with
deionized water to ensure
adhesion to the holder.
c) While applying a
vacuum to the filtering
flask, transfer the sample to
the filtering apparatus.
d) Slowly release the
vacuum from the filtering
flask and transfer to
another container.
12. Continue the
analysis using one of the
following procedures.
Use metals or
TKN procedure
GENERAL DIGESDAHL DIGESTION, continued
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