General Digesdahl Digestion - Hach Digesdahl 23130-20 Instrument Manual

GENERAL DIGESDAHL DIGESTION

1.
Transfer a
preweighed or a
premeasured amount of
sample into a 100-mL
Digesdahl digestion
flask; see Table 1 on
page 22. The amount
transferred should not
contain more than 0.5 g
of solids or organic
liquids. The maximum
volume for water
samples is 40 mL. In
samples with more than
1% solids present, use
the formula below:
Water Sample Volume
= 40 ÷ % solids
Note: Use only Hach
digestion flasks. Volumetric
flasks with concave bottoms
should not be used.
Note: If solids are 10% of
total volume of sample, the
maximum volume of liquid
sample would be 4 mL.
Note: Several 40-mL
sample aliquots of the
sample may be digested in
succession to concentrate
a sample.
Note: If liquid is too
viscous to measure,
preweigh the sample into
the digestion flask.
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2.
Add concentrated
sulfuric acid (according
to Table 1 on page 22) to
the volumetric flask and
at least two silicon
carbide boiling chips for
liquid samples.
Note: Pretreat boiling
chips by soaking in 1:1
Nitric Acid and rinsing
thoroughly with deionized
water. Treatment is very
important in low-level
work. Hach recommends
silicon carbide boiling
chips.
3.
Turn on the water to
the aspirator and make
sure there is suction to
the fractionating
column. Turn the
temperature dial to a
heat setting of 440 ° C
(825 ° F). For meat
digestion, set to 468
(875 ° F).
Note: Wait for the proper
temperature to be reached
before the sample is placed
on the heater.
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4.
Place the flask
weight followed by the
fractionating column
with funnel on the flask.
Place the flask on the
heater and heat until the
sulfuric acid boils
(refluxing sulfuric acid
°
C will be visible).
Note: White acid vapors
usually will be present, but
their presence alone does
not indicate that the boiling
point of sulfuric acid has
been reached.
Note: Liquid samples
require total evaporation of
water before vapors
are visible.
Note: If sample foams up
into the neck of the flask,
lower temperature to
335 ° C (635 ° F). Continue
heating at lower
temperature until all water
is evaporated. Then return
to original digestion
temperature.
Note: If foaming or
bumping is not stopped by
lowering temperature or
volume, then liquid samples
that will not clog the
capillary funnel may be
added to the flask via the
capillary funnel, 10 mL at a
time. Decrease amount
added if foaming persists.
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