Velp Scientifica
– UDK139 Operating Manual
10004762/B5
98
28 - Kjeldahl method to determine gelatin on paper
During paper manufacture animal glue or gelatin, casein and soya proteins are used
as bonding agents. Kjeldahl’s method gives reliable results for the protein content if
other nitrogen compounds are not present (e.g. synthetic resins for improving
resistance to humidity).
Procedure
1) Sample
2 g about of paper cut in pieces of 1 cm
2
2) Reagents for digestion
To each sample add in the test tube:
2 catalyst tablets ST (code CT0006609)
15 ml concentrated sulphuric acid (96-98%).
3) Digestion
Heat at 200 °C for some minutes to let the foam develop, then go to 420 °C for 30
minutes.
4) Cooling
Let cool test tubes to 50-60 °C
5) Distillation-titration:
place in position the test tube with the digested sample in
the unit UDK 139.
factor: 5.60
Addition of reagents:
dilution water= 50ml
H
3
BO
3
= 30ml
NaOH= 50 ml
Titrant: H
2
SO
4
0.1 N
Distillation time= 4 min
Steam power= 100%
Press the button starting distillation cycle.
References:
TAPPI Standard T418 05-61. Organic Nitrogen in Paper, modified by reducing to the
half the quantity of mercury catalyst.
TAPPI Standards and Suggested Methods. Technical Association of the Pulp and
Paper Industry. Atlanta, Georgia, USA.
285
