Velp Scientifica
– UDK139 Operating Manual
10004762/B5
94
24 - Kjeldahl method to determine total nitrogen on ABS, SAN,
rubber
Procedure
1) Sample:
RUBBER: the sample is cut in small pieces and then ground.
0,5 g of sample accurately weighed are used for the analysis.
SAN: cut in small pieces the sample . Grind it. Pellets of 1x3 mm can be directly
analysed. Weigh 0.50 g of sample with an accuracy of
2 mg.
ABS: grind the sample. Weigh 0.50g with an accuracy of
2 mg. Pellets of 1x3 mm
can be directly analysed.
2) Reagents for digestion:
2 catalyst tablets CM (code CT0006650)
2 Antifoam tablets S (code CT0006600)
15 ml concentrated sulphuric acid (96-98%)
5 ml Hydrogen peroxide 30-32 % (added 1 by 1 ml).
after the addition of reagents shake to wet the sample.
In some cases it could be necessary to pre-digest the samples overnight at room
temperature.
3) Digestion
:
30 min at 250 °C
30 min at 350 °C
60 min at 420 °C.
4) Cooling:
let cool the test tubes to 50-60 °C.
5) Distillation-titration:
place in position the test tube with digested sample in the
unit UDK 139.
factor: 6.25
Reagents addition:
dilution water= 50ml
H
3
BO
3
=30ml
NaOH (40% w/v) = 60 ml
Titrant: HCl 0.1N
Distillation time= 4 min
Steam power= 100%
Press the button starting distillation cycle.
References:
ISO norm n. 1656
281