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Aquaprobe
®
AP-7000 Instruction Manual
10401-00894 Rev M
16.5. 7000-NIT Nitrate Electrode
Nitrate (NO3) can be measured by the AP-7000 using the optional 7000-CHL ISE electrode
within a pH range of 3 – 10.
The Nitrate ISE electrode will suffer interference from Chloride, Bromide, Fluoride,
Sulphate, Chlorate and Perchlorate ions, which are similar in nature.
16.5.1.
Nitrate Calibration Solution Preparation
When a Nitrate ISE electrode is first installed, it must be calibrated at three points. In order
to achieve this, three batches of Nitrate calibration solution must be prepared.
The solutions required are two 400mL batches of Nitrate at a concentration of 10ppm and
one 500mL batch of Nitrate at a concentration of 100ppm.
The three calibration solutions should be freshly prepared by serial dilution from 1000ppm
calibration standard. The following Nitrate standard is recommended:
Part number: SS-712-1610
Description: 500mL Nitrate 1000ppm ISE
Supplier: T E Laboratories Ltd, Ireland.
Contact:
Be sure to handle chemicals with care and to read and comply with all health and
safety advice.
Preparing the 100ppm solution
500mL of 100ppm solution is required. To prepare this, mix 50mL of 1000ppm calibration
standard with 450mL of deionised water.
Dispense 400mL of the 100ppm solution into a calibration cup and retain 100mL for
preparation of the 10ppm solution.
Preparing the 10ppm solution
A total of 800mL of 10ppm solution is required. To prepare this, mix 80mL of the 100ppm
solution you have just prepared with 720mL of deionised water. Dispense the 10ppm
solution into two calibration cups (400mL each).
Achieving the correct temperature
During three point calibration, the 100ppm solution and one batch of the 10ppm solution
must be at exactly the same temperature. The second batch of 10ppm solution must be at
least 10ºC cooler.
In order to achieve this, one batch of the 10ppm solution should be put into a refrigerator
and the other two solutions should be put into a water bath at 25ºC.
Once all three solutions are at a stable temperature, calibration can begin.
16.5.2.
Three-point Calibration
During three-point calibration, the AP-7000 and Aquameter
®
must remain switched on. If
the Aquameter
®
is switched off between points, the calibration process will be aborted and
must be re-started from point 1.
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®
Ltd.
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