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

Instruction Manual Nitrate Ion Electrode
3
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
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 a 2% measurement error.
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, between the stirrer and beaker.
Always rinse the electrodes with distilled water and blot dry between measurements. Use a clean, dry
tissue to prevent cross-contamination.
For samples with high ionic strength, prepare standards whose composition is similar to the sample.
Always check to see that the membrane is free from air bubbles after immersion into standard or
sample.
A slow responding electrode may be caused by interferences to the electrode. To restore proper
performance, soak the electrode in distilled water for about 5 minutes to clean the membrane, rinse, and
soak in standard solution for about 5 minutes.
Sample Requirements
All samples must be aqueous and not contain organics which can dissolve in the membrane or extract
out the liquid ion exchanger.
The temperature of the standard solutions and of the sample solutions should be the same and below
40
o
C. About a 2% error will be introduced for a 1
o
C difference in temperature.
Interferences should be absent. If they are present, use the procedures found in the
Interferences
section to remove them.