BUCHI KjelSampler K-377 - Manual (Page 39)

4 Description of function
39 K-375/376/377 Operation Manual, Version B
4 .7 Blank values
The K-375 differentiates between blanks and control blanks. Blanks are performed to correct minimal
contamination of chemicals on sample determination (sample and reference substance).
Control blanks are performed to check the determination process for cross contaminations and are
not used for calculation.
The determination and the definition of blank values is described in chapter 6 Operation.
4 .7 .1 Blanks
It is recommended to run blank values with exactly the same method as the subsequent samples.
The blank values may vary, depending on the receiver solution (e.g. concentration of the boric acid,
amount of indicator added, pH value set), the concentration of the titration solution, and the purity of
chemicals.
It is recommended to perform blank values, if:
• Fresh chemicals are used or
• Before starting determination in order to check the system.
If a blank value is activated for calculation, it remains active, until another blank value is activated.
4 .7 .2 Control blanks
A control blank enables to check for crosscontamination, 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.
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 chapter 3, Technical data.
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 Determina-
tion” for details.
4 .9 Result Groups
Each result of a sample determination can be assigned to a group, e.g. the results of samples taken
from the same batch/lot, place, at the same day, etc. can be assigned to the same result group.
All results in the same group are treated the same way regarding sample printout and export of data.