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

Instruction Manual Cadmium Electrode
5
5. To a 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%. If the slope is not within this range,
see the
TROUBLESHOOTING
sections if the slope is not within this range.
MEASUREMENT
Measuring Hints
All samples and standards should be at the same temperature for precise measurement. A difference
of 1
o
C in temperature will result in about a 2% measurement error.
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 a styrofoam sheet, between the stirrer and beaker.
Always rinse the electrode tips with distilled water and blot dry. Use a clean, dry tissue to prevent
cross-contamination.
For samples with high ionic strength, prepare standards whose composition is similar to the sample.
Use fresh standards for calibration.
Use 2 ml of ISA for each 100 ml of sample or standard.
Always check to see that the membrane is free from air bubbles after immersion into the standard or
sample. Dilute concentrated samples (>0.1M) before measurement.
Sample Requirements
All samples must be aqueous and not contain organics which can dissolve the epoxy electrode body
and/or the cement bonding the sensing crystal to the electrode body. Infrequent measurements in
solutions containing methanol, benzene, or acetonitrile are permitted. Highly polar solvents slowly
attack the electrode. Please check with Eutech Instruments Pte Ltd. before using these electrodes in
other organic solvents.
The temperature of the sample solutions and of the standard solutions should be the same and below
80oC. About a 4% error in the slope will occur for each 1
o
C difference in temperature. Interferences
should be absent. If they are present, use the procedure found in the
Interference
and
Electrode
Response
sections to remove them.
Adjust sample pH with 1M HNO
3
to below pH 7 to avoid precipitation of cadmium hydroxide,
Cd(OH)
2
.