Thermo Fisher Scientific Dioxide Ion Selective Electrodes Carbon - Manual (Page 5)

Instruction Manual Carbon Dioxide Electrode
5
2. Using a pipet, add 1 ml of 0.1M or 1,000 ppm standard into the solution. When the reading
has stabilized, record the mV value.
3. Using a pipet, add 10 ml of the same CO
2
standard used above to the beaker. When the
reading has stabilized, record the mV value.
4.
Determine the difference between the two readings. The electrode is operating correctly if
a difference of 56
± 3 mV is found, assuming the solution temperature is between 20 o
and
25
o
C. See the
TROUBLESHOOTING
section, if the change in potential 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 carbon dioxide solutions whose concentrations vary by tenfold. Use
either the 0.1M or 1,000 ppm carbon dioxide standard. Use the serial dilution method for
this preparation.
2.
To a 150 ml beaker, add 100 ml of the lower value standard and 1 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. Rinse the electrodes with distilled water
and blot dry.
4.
To another 150 ml beaker, add 100 ml of the higher 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.
5.
Adjust the meter to the concentration of the standard and fix the value in the memory.
Read the electrode slope according to the meter manufacturer's instructions. Correct
electrode operation is indicated by a slope of 90-100%. See the
TROUBLESHOOTING
section if the slope is not within this range.
MEASUREMENT
Measuring Hints
Samples should be measured immediately after collection. Samples should be stored according to
the directions given in
Sample Storage
if immediate measurement is not possible.
The ratio of surface area to volume in the beaker should be minimized. Beakers containing the
samples or the standard should be kept covered between measurements.
Carbon dioxide buffer should be added just before measurement.