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Table 8. Digestion Guidelines for Specific Sample Types (continued)
Sample Sample Amount Preheat Amount of Special
Type Weight of Acid Time Peroxide Instructions
Edible 0.25 to 0.5 g 4-6 mL 4 min. 5 mL Weigh sample into
Oils immediately flask and record
and 5 mL exact weight.
later
Ion equivalent 10 -15 mL 12 min. 20 mL Digest will be clear
Exchange of 0.25 g with particles on
Resin dry resin bottom if metal
oxides are not
soluble in H
2
SO
4
.
Add aqua regia or
suitable solvent to
dissolve particles.
If particles are
floating, start again
using 15 mL H
2
SO
4
and longer char
time.
Soil 0.25 to 1.0 g 6 mL 4 min. 10 to 20 mL
Fuels/ 0.25 to 0.5 g 6 mL 4 min. 20 mL Heat the diluted
Lubricants digest for 15
minutes and filter.
Temperature of
heater may need to
be lowered slightly
if foaming or
burning occur.
SAFETY CONSIDERATIONS
Digesdahl Digestion Apparatus
For safe Digesdahl operation:
•Sample size-Never exceed 0.5 grams of sample (dry weight)
•Oils and organic liquids should be considered as solids when
determining sample size.
•Acid type- Only use acid specified in Hach step-by-step procedures.
•Acid volume- Never use less than 3 mL.
•Always follow the order of steps indicated.
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