5 device monitoring – BUCHI KjelSampler K-377 User Manual

Page 124

7 Maintenance

124

K-375/376/377 Operation Manual, Version B

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 =0.1218 (12.18 %)

Original sample weight:

200 mg

Receiving solvent:

Boric acid 4 %, adjusted to pH 4.65 (with NaOH)

Titration solution:

Sulfuric acid 0.1 mol/L

Determination method:

Standard

Number of Blank Values:

≥ 3

Acceptable RSD Blanks:

≤ 5 %

Number of Samples:

≥ 3

Acceptable Recovery Rate
Standard:

98.0 ... 102 %

Acceptable RSD:

1 %

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 tablets

Catalyst amount:

2 tablets

Sulfuric acid conc. 98%:

15 mL

Digestion temperature:

Preheat to 320° C, digest at 420 ° C

Digestion time:

120 min