Thermo Fisher Scientific Ion Selective Electrodes Nitrate - Manual (Page 4)

Instruction Manual Nitrate Ion Electrode
2
dissolve the solid. Fill to the mark with distilled water, cap and upend several times to mix
the solution.
GENERAL PREPARATION
Electrode Preparation
Remove the rubber caps covering the electrode tips and any rubber inserts covering the filling holes of
the reference electrode. Fill the combination electrode or the reference electrode with the filling
solution shipped with the electrode to a level just below the fill hole. No preparation is required with a
sealed reference electrode. Gently shake the electrode downward in the same manner as a clinical
thermometer to remove any air bubbles which may be trapped behind the nitrate membrane. Prior to
first usage, or after long-term storage, immerse the nitrate membrane in nitrate standard for thirty
minutes. The electrode is now ready for use.
Connect the electrodes to the proper terminals of the meter as recommended by the meter manufacturer.
Electrode Slope Check (with pH/mV meter)
(check electrodes each day)
1.
To a 150 ml beaker, add 100 ml of distilled water and two ml of ISA. Place the beaker on a
magnetic stirrer and begin stirring at a constant rate. After assuring that the meter is in the
millivolt mode, lower the electrode tips into the solution.
2.
Using a pipet, add 1 ml of 0.1M or 1,000 ppm nitrate standard to the beaker. When the reading
has stabilized, record the mV reading.
3.
Using a pipet, add 10 ml of the same nitrate standard used above to the beaker. When the
reading has stabilized, record the mV reading.
4.
Determine the difference between the two readings. The electrode is operating correctly if the
millivolt potential has changed by 56 ± 2 mV, assuming the solution temperature is between
20
o
and 25
o
C. See the
TROUBLESHOOTING
sections if the potential change is not within this
range.
Slope is defined as the change in potential observed when the concentration changes by a factor of 10.
Electrode Slope Check (with ion meter)
(check electrodes each day)
1. Prepare standard nitrate solutions whose concentrations vary by ten fold. Use either the 0.1M
or 1,000 ppm nitrate standard. Use the serial dilution method for this preparation.
2.
To a 150 ml beaker, add 100 ml of the lower value standard and 2 ml of ISA. Place the beaker
on the magnetic stirrer and begin stirring at a constant rate. Lower the electrode tips into the
solution. Assure that the meter is in the concentration mode.
3.
Adjust the meter to the concentration of the standard and fix the value in the memory
according to the meter manufacturer's instructions.