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

Calcium Electrode Instruction Manual
4
flask gently to dissolve the solid. Fill to the mark with distilled water, cap, and upend
several times to mix the solution.
6.
EDTA titrant, 1M stock solution, for the titration of calcium. To prepare this titrant, add
37.2 grams of reagent grade Na
2
EDTA.2H
2
O, ethylenediaminetetraacetic acid dihydrate,
disodium salt, to a 100 ml volumetric flask, add about 75 ml of distilled water, and swirl
the flask gently to 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 the rubber insert covering the filling hole 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 might be trapped behind the calcium
membrane. Prior to first usage, or after long-term storage, immerse the calcium membrane in
calcium standard for thirty minutes. The electrode is now ready for use.
Connect the electrodes to the proper terminals 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. 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. If drifting or instability is observed, see the
TROUBLESHOOTING
section.
2.
Using a pipet, add 1 ml of 0.1M, 1,000 ppm, or 100 ppm (as calcium carbonate) standard
and 2 ml of ISA to the beaker. When the reading is stable, record the mV reading.
3.
Using a pipet, add 10 ml of the same calcium 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 mV potential has changed by 27±2 mV, assuming the solution temperature is between
20
o
and 25
o
C. See the
TROUBLESHOOTING
section 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.