wtw AmmoLyt 700 IQ, Руководство по эксплуатации

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Calibration and measuring AmmoLyt
®
700 IQ
4 - 16 ba75353e05 03/2006
4.1.9 Calibration procedure, Double std. add. (5)
This calibration with double standard addition is carried out in the test
sample while adding standard with a certain concentration in two steps.
The volumes of test sample and standard have to be dosed exactly.
The following appliances are suitable for dosing:
!
Measuring cylinder to determine the volume of the sample
!
Pipette to exactly dose the standard
Note
Before
calibrating, determine the potassium content of the sample (see
section 4.2.2).
Before calibrating, activate the Potassium compens. function and
adjust the potassium content (see section 3.4).
The potassium content of the test sample affects the calibration result.
Concentration and
quantity of standard
solution
The quantity of standard solution to be added is permanently fixed for
the double standard addition:
!
First addition: 1 % of the sample volume
!
Second addition: 2 % of the (original) sample volume
After both additions, the original ammonium content of the test sample
should be increased at least twofold but not more than tenfold.
Based on these conditions, the range that can be calibrated is from 2.5
to 220 mg/l NH4-N (or 3.2 to 283 mg/l NH4). If the expected measured
values are outside this range, a different calibration procedure has to
be selected.
The concentration of the standard solution to be added depends on the
measuring range expected. It can be determined by means of the follo-
wing diagram. The requirements for the double standard addition are
automatically met while doing so.