7 Maintenance
K-375 / K-376 / K-377
Operation Manual, Version E
126
7 2 5
Device monitoring
In order to test/check the instrument, a nitrogen determination with a reference substance can be
carried out. We recommend the following parameters as standard application.
Parameters for checking the distillation and titration procedure with ammonium dihydrogen phos-
phate:
Check:
Distillation and titration
*Reference substance:
Ammonium dihydrogen phosphate min 99.5 %
Nitrogen content:
w =0.1212 (12.12 %)
Original sample weight:
200 mg
Receiving solvent:
Boric acid 4 %, adjusted to pH 4.65 (with NaOH)
Titration solution:
0.2 N (HCl or H
2
SO
4
)
Determination method:
Standard
Number of blank values:
≥
3
Acceptable RSD blanks:
≤
5 %
Number of samples:
≥
3
Acceptable recovery rate
reference substance:
99.5 ... 102 %
Acceptable RSD:
1 %
* this is only a guideline; please verify and use your specific purity of the reference substance. There-
fore check the respective “Certificate of Analysis” which is delivered from the manufacturer of the
reference substance and create a modified reference substance according to it.
Parameters for checking the digestion, distillation and titration with glycine
Check:
Digestion, distillation and titration
Reference substance:
Glycine (99.7 %)
Drying before analyzing:
8 h at 105 °C
Nitrogen content:
w = 0.1866 (18.66 %)
Original sample weight:
200 mg
Kjeldahl catalyst:
Titanium BUCHI Kjeldahl Tablets
Catalyst amount:
2 tablets
Sulfuric acid conc. 98 %:
15 mL
Digestion temperature:
see BUCHI Application Notes
Digestion time:
see BUCHI Application Notes
Receiving solvent:
Boric acid 4 %, set to pH 4.65 (with NaOH)
Titration solution:
0.2 N (HCl or H
2
SO
4
)
Determination method:
Standard
Number of blank values:
≥
3
Acceptable RSD blanks:
≤
5 %
Number of samples:
≥
3
Acceptable recovery rate
reference substance:
98.0 ... 102 %
Acceptable RSD:
1 %
