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

Instruction Manual Potassium Electrode
5
4. Rinse the electrodes with distilled water and blot dry.
5.
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.
6.
Adjust the meter to the concentration of the standard and fix the value in the memory.
7.
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
All samples and standards should be at the same temperature for precise measurement, preferably
ambient temperature.
The sensing membrane is normally subject to water uptake and might appear milky. This has no
effect on performance.
Constant, but not violent, stirring is necessary for accurate measurement. Magnetic stirrers can
generate sufficient heat to change the solution temperature. To counteract this effect, place a piece
of insulating material, such as styrofoam sheet or asbestos sheet, between the stirrer and beaker.
Always rinse the electrode tip(s) with distilled water and blot dry with a fresh tissue between
readings to prevent solution carryover.
Check the electrode for air bubbles adhering to the membrane surface after immersion in solution.
Agitate the electrode gently to remove the air bubbles.
A slow or sluggish electrode response may indicate surface contamination of the potassium
electrode membrane. Soak the electrode tip in distilled water for about 5 minutes to clean the
membrane. Rinse the membrane and soak in diluted standard solution for about 5 minutes to restore
performance.
When measuring samples with high ionic strength, prepare standards with compositions similar to
that of the sample.
Dilute concentrated samples (over 0.1M) before measurement. Recalibrate every few hours for
routine measurement.
Sample Requirements
Make sure that the samples and standards are at the same temperature. About a 2% error will be
introduced for a 1
o
C difference in temperature. Temperature should normally be less than 40
o
C with
intermittent measurements allowed to 50
o
C.