INSTRUCTION MANUAL
CODE 80189 REV E
12/2020
Page: 66
J
.P. SELECTA s.a.u.
Autovía A-2 Km 585.1 Abrera 08630 (Barcelona) España
Tel 34 937 700 877 Fax 34 937 702 362
e-mail: [email protected] - website: http://www.jpselecta.es
12 Kjeldahl analysis step by step
12.2 Digestion
• Add between 10-15ml (MACRO tube) of H
2
SO
4
96-98% and one catalyser
tablet (8gr) (for MICRO tube maximum H
2
SO
4
is 5ml).
• Rig up a system for smoke extraction or scrubber with Na
2
CO
3
.
• Make this digestion in 3 steps:
1.
According to the level of water in the sample, begin digestion at 150ºC for 20
or 60 minutes.
2.
Make a second step by 280ºC for 30 minutes to reduce white smoke produc
-
tion.
3.
Continue the digestion with 400ºC for 60-90 minutes.
Visual checking:
the result is a neat transparent liquid with a clear blue colora-
tion or green or yellow depending on the catalyser used. No black rest must be
stuck on the tube’s wall.
Note:
During digestion you must control foam production in the samples. If there
is too much foam, length step 1.
12.1 Sample preparation
• Triture, homogenize and mix the sample.
• Weight between 1 and 2 grams of the sample.
• In low nitrogen content samples, (waste waters, etc...) take enough sample to
get 5mg nitrogen.
12.4 Distillation
• Check the tank level of NaOH and Boric acid. Check the dispensing pumps are
primed and give the correct volume.
• Put a 250ml Erlenmeyer in the outlet cooler with 50ml Boric acid and some
indicator drops.
• Program a 50 to 75 ml NaOH dosage (35ml for MICRO tube).
• Program the HCl normality.
• Insert the tube with the sample in the distiller.
• Initiate distillation / titration.
• The PRO-NITRO «A» shows the nitrogen detected at the end of the analysis
Visual checking
: Once the NaOH has been added, the sample must get a blue
coloration, if not add more NaOH. It can be added more NaOH by pressing «
»
before titration display appears.
12.5 Protein % content calculation
• Apply the protein factor, according the sample type. Use:
P2: Nitrogen (mg).
P0: Sample weight (mg).
F: Protein factor.
(6.25 default)
% Protein =
P
2
x 100 x F
P
0
12.3 Dilution
• Take out the sample tube off the digester block and let it cool to ambient tem
-
perature.
• Add about 25ml of water in each tube (10ml for MICRO tube).
• Slow add water, moving the tube to not let solidify the sample. Heat the tube if
necessary. (e.g. introducing the tube into the digester block)
• Let it cool again.
• To avoid nitrogen loss and violent reactions do not introduce the hot tube
inside the distiller.
