INSTRUCTION MANUAL
CODE 80187
REV D
01/2021
Page: 38
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.grupo-selecta.com
8.4
Checking Nitrogen recovery with Acetanilide.
This test is widely used to certify the whole Kjeldahl analysis process, including the
digestion, distillation and titration steps.
It consists in preparing some samples that have a known Nitrogen content. The
samples are digested, distilled, titrated and the nitrogen detected is calculated.
The rate (%) of nitrogen detected versus the sample Nitrogen content gives us the
Nitrogen Recovery
.
To run this test Acetanilide is used.
Preparing the sample:
Nitrogen content of an acetanilide sample:
Formulae: C
8
H
9
NO
Molecular weight: 135.17
Factor: 14 / 135.17 = 0.1035 mg of Nitrogen = 0.1035 * mg Acetanilide.
• Weight around 250mg (100mg) of acetanilide. The exact weight P
0
• The Nitrogen content is:
P
1
(mg) = P
0
x 0,1035
Sample digestion:
• Place the acetanilide on a MACRO tube, add 10ml of Sulphuric acid 98% (Exam
-
ple PANREAC 173163) and one tablet of Kjeldahl catalyser.
• Digest at 400ºC for 1h. (The result must be a transparent blue liquid)
• Let cool at ambient temperature. Add 25ml of distilled water on each tube.
Operate with caution to avoid splash. Water reaction over the sulphuric acid could
be violent.
Distillation:
• Distillate by adding 75ml of NaOH. Use HCI 0.25N (0.1N) for titration.
• Once sample is distilled and titrated following chapter 6, the detected Nitrogen
is calculated as: P
2
• Recovery is calculated as:
R(%) = P
2
/ P
1
*100
• Acceptable recovery is from 99.0 to 101.5 %.
Note:
If MICRO size tube is used, weight 0.3g of acetanilide, add 5ml of sulphuric acid,
and one tablet of Kjeldahl catalyser. On the dilution add 10ml water.
Distillate for 6 minutes adding 25ml of NaOH.
Note:
Some literature sets that the acceptable values for recovery must be above
99.5%. To get these results you must work with high precision and use reagents
with high degree of purity.
