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INSTRUCTION MANUAL CODE 80188 REV E
J
.P. SELECTA s.a.u.
Jun/2018
12 Kjeldahl analysis step by step
12.1 Sample preparation
•
Triture, homogenize and mix the sample.
•
Weight between 1 and 2 grams of the sample.
•
In low nitrogen content sample, (waste water, etc...) take enough samples to
get 5mg nitrogen.
12.2 Digestion
•
Add between 10-15ml (MACRO tube) of H
H
SO
is 5ml).
2
4
•
Rig up a system for smoke extraction or scrubber with NaOH.
•
Make this digestion in 3 steps:
1. In function of 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. It must not still black
rests 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.
12.3 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.
12.4 Distillation
•
Check the tank level of NaOH and Boric acid. Check the dispensing bombs are
primed and give the correct volume.
•
Put a 250ml Erlenmeyer in the outlet cooler and add 50ml Boric acid and some
indicator drops.
•
Program a 50 to 75 ml NaOH dosage (25ml for microtube).
•
Insert the tube with the sample in the distiller.
•
Distillate till recollecting 250ml in the Erlenmeyer (50ml Boric acid+200ml of
distillate).
Visual checking: Once the NaOH has been added, the sample must get a blue
coloration, if not add more NaOH.
12.5 Titration and calculations
•
Titrate the distilled with HCl or H
point: pH 4.65).
•
Calculate: mg of Nitrogen = 14 * Volume
•
Calculate protein contents correct with the right factor based on the sample
nature. (6.25 default value)
•
Periodically make a blank test and subtract it from the result.
Autovía A-2 Km 585.1 Abrera 08630 (Barcelona) España
e-mail: selecta@jpselecta.es - website: http://www.jpselecta.es
(It can be modified without notice)
SO
(for MICRO tube maximum
2
4
SO
0.1 or 0.25 N till colour changes (end
2
4
* Normality
HCl
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