Epa Vigorous Digestion With Hot Plate - Hach DR/700 Procedures Manual

6. Quantitatively transfer the sample with deionized water to a 100-mL
volumetric flask and dilute to volume with deionized water. Continue
with the procedure. This mild digestion may not suffice for all sample
types. A reagent blank also should be carried through the digestion and
measurement procedures.

EPA Vigorous Digestion with Hot Plate

For Metals Analysis Only
A vigorous digestion can be followed to ensure all organo-metallic
bonds are broken.
1. Acidify the entire sample with redistilled 1:1 Nitric Acid Solution to a
pH of less than two. Do not filter the sample before digestion.
2. Transfer an appropriate sample volume (see table below) into a beaker
and add 3 mL of concentrated redistilled nitric acid.
3. Place the beaker on a hot plate and evaporate to near dryness, making
certain the sample does not boil.
4. Cool the beaker and add another 3 mL of the concentrated redistilled
nitric acid.
5. Cover the beaker with a watch glass and return it to the hot plate.
Increase the temperature of the hot plate so that a gentle reflux occurs.
Add additional acid, if necessary, until the digestion is complete
(generally indicated when the digestate is light in color or does not
change in appearance with continued refluxing).
6. Again, evaporate to dryness (do not bake) and cool the beaker. If any
residue or precipitate results from the evaporation, add redistilled 1:1
hydrochloric acid (5 mL per 100 mL of final volume). See Table 7 below.
7. Warm the beaker. Add 5 mL of 5.0 N sodium hydroxide and
quantitatively transfer the sample with deionized water to a volumetric
flask. See Table 7 below for the size of flask.
8. Adjust the sample to pH 4 by drop-wise addition of 5.0 N Sodium
Hydroxide Standard Solution; mix thoroughly and check the pH after
each addition. Dilute to volume with deionized water. Multiply the
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