multi N/C 2100S (duo, pharma)
Function and design
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3.5
Catalysts
As an oxygen carrier, the catalyst supports combustion of the samples. Solids that are
catalytically active in a temperature range of 700 to 950 °C can be used as catalysts.
The platinum catalyst can be used universally over the entire working range for carbon
and nitrogen determination. Its optimal function is at a reaction temperature of 800 °C.
Because of its very low individual blank value, it allows safe and precise analysis of low
carbon and nitrogen contents. The catalyst also works effectively during analysis of
highly contaminated waters.
To minimize wear, reducing the furnace temperature to temperatures below the melting
point of the salts is recommended with high salt matrices (e.g., seawater).
Alternatively, a CeO
2
catalyst can be used at a reaction temperature of 850 °C.
3.6
Calibration
3.6.1
Calibration strategies
Multiple point calibration with constant sample volume
In many applications, multiple point calibration with a constant dosage volume and mul-
tiple standard solutions at different concentrations is suitable.
The calibration range can encompass a wide range of concentrations and must be de-
fined in accordance with the expected sample concentrations. Multiple standard solu-
tions are measured with the selected method.
Multiple point calibration with constant concentration
Additionally, a multiple point calibration with variable dosage volumes and constant
concentration can be performed. This calibration strategy is particularly interesting and
the norm in the pharmaceutical industry for measurements at very low concentrations
(<1 mg/l).
Only create one standard solution for the calibration range. The analyzer then analyzes
different volumes of this standard solution. Do not go below the lowest standard solu-
tion volume of 2 ml when doing this.
Check the calibration via a second independently made standard solution to exclude er-
rors during standard solution creation.
Take the blank value of the preparation water into account for measurements in the
range of low concentration (<10 mg/l).
Single point calibration
For low TOC concentrations such as those in the pharmaceutical industry, single point
calibration is a very good solution. A big advantage is that the device blank value is low
and that the NDIR detector performs linear measurement across a wide range of con-
centrations.
Proceed as follows to minimize errors during manual standard solution creation:
¡
Prepare 3 standard solutions at the same concentration.
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Measure the standard solutions.
¡
Determine the calibration curve from the average value in the results.
