Velp Scientifica
– UDK139 Operating Manual
10004762/B5
95
25 - Kjeldahl method to determine total nitrogen in urea
The method is suitable for the determination of urea content in aminoplastics, i.e.
urea-formaldehyde resins.
Procedure
1) Sample
: the sample is ground in order to obtain a powder very fine and
homogeneous .
1g of sample accurately weighed is quantitatively transferred in a test tube.
2) Reagents for digestion.
for each sample add in the test tube:
2 catalyst tablets CM (code CT0006650)
12ml concentrated sulphuric acid (96-98%)
after the addition of reagents shake to wet the sample.
3) Digestion
: 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: 0.00
Addition of reagents:
dilution water= 50ml
H
3
BO
3
= 30ml
NaOH= 50 ml
Titrant: HCl 0.2N
Distillation time= 4 min
Steam power= 100%
Press the button starting distillation cycle.
The urea content of the sample is calculated considering that the nitrogen content of
urea is 46.65%.
The quantity of distilled ammonia from 0.1g of urea requires 16.64ml of 0.2N HCl to
be titrated.
References:
ISO norm n. 1392.
282