4 Description of function
K-375 / K-376 / K-377
Operation Manual, Version E
39
4 7 2
Control blanks
A control blank enables to check for cross contamination, e.g. in the middle of a rack, without
affecting the calculation of the following samples.
Example
:
Determination of
3 blanks, 6 samples, 1 control blank, 10 samples in a 20-position rack.
All samples are calculated with the mean value of blank 1-3. The control blank allows to check the
system without interruption.
Fig. 4.8: Example of rack containing a control blank
4.8 Reference substances
Reference substances are substances with known nitrogen content and serve to check the perfor-
mance of the system and the application.
It is recommended to analyze reference substances regularly. For information on reference
substances, see table.
A check of the K-375 without digestion is done with a standardized ammonium salt (e.g. ammonium
di-hydrogen phosphate).
In order to check the entire Kjeldahl process (including digestion), standardized amino acids are used
(e. g. Glycine).
The determination of reference substances is done like a normal sample determination (Sample type:
“Reference substance”) as single sample, sample list or a sequence. See Chapter “6.6 Determination”
for details.
