Labconco Rapid Digestors 23080 - Manual (Page 10)

NORMAL OPERATION
11
Operation and General Kjeldah Digestion Procedure for Nitrate Free Samples 1 - 2
General Digestion for feed, grain, etc.
1. Turn main power switch located on front of controller to ON position. Set temper-
ature to 410°C using temperature set point dial on controller. Allow approximately
one hour for unit to reach pre-set temperature (digestor at pre-set temperature when
light(s) located on front of digestor is flashing).
2. Carefully insert the digestion tubes into the holes provided in the flask rack. The
flask rack can be used for convenient handling and transportation of the digestion
tubes.
3. Place weighed, well ground homogenous samples into digestion tubes and add 9g
K2SO4, 0.42 g Hg0, and 15 ml H2SO4.
4. After completing sample and reagent addition to the digestion tubes, carefully elevate
the rack by grasping the handles provided and place in position on the digestor unit.
As the rack is lifted, each tube will rest on its top rim. Carefully lower rack so that
each tube enters its respective hole and bottoms in the base of the unit.
5. If optional fume removal system has been purchased, place system on top of the
digestion tubes. Alignment is accomplished by a side to side, front to back motion.
Adjust water flow to aspirator to the point where all fumes are removed. (Refer to
instruction manual for Fume Removal System).
6. Place end plates on flask rack. These plates completely close the ends of the flask
rack and allow the temperature of the upper portion of the tube to elevate providing
for proper refluxing and condensation of the H2SO4 which washes the carbonized
material back into the digestion solution. (A certain amount of roaming will occur at
the beginning of the digestion. The refluxing of the acid washes any carbonized
material back into the digestion solution. If foaming is uncontrollable, reduce
digestion temperature and/or sample size).
7. Digest sample at 410° for 45 minutes for complete recovery of all types of nitrogen
containing samples. (Digestion time may be less for those samples not containing
refractory nitrogen. Refer to Labconco’s extracts).
Official Methods of Analysis of the Association of Official Analytical Chemists,
Thirteenth Edition, Washington, District of Columbia, 1980.
Methods utilizing copper as the catalyst and 20 minute digestions refer to reference
section of this manual and request appropriate Labconco extracts.
8. After digestion is complete, remove flask rack containing tubes from digestor and
place on heat resistant pad. Avoid having the hot tubes come into contact with a cool
or wet surface. (As a safety precaution, wear asbestos gloves and goggles when
removing the rack and tubes from the digestor).