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

Instruction Manual Sodium Electrode
3
4.
Rinse the electrodes with the electrode rinse solution 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 a 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. A difference of 1
o
C in temperature will result in about a 2% measurement
error. The electrodes should not be used above 70
o
C.
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 the beaker.
Always rinse the electrodes with electrode rinse solution from a wash bottle between
measurements. Use a clean, dry tissue to prevent cross contamination. Never use distilled water.
Store the electrodes in electrode storage solution between measurements. Do not store in air or
distilled water. Always soak new electrodes overnight in electrode storage solution prior to first
use. When making low level sodium measurements, use a dilute sodium chloride storage solution.
Add 1 ml of ISA to 100 ml of dilute storage solution.
Plastic lab-ware should be used for low level measurements (<1 ppm). All measurements should be
made in basic solution. All samples and standards should be adjusted to a pH > 9 with ISA.
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.
Sample Requirements
The sample measuring range is pH 9-12. Use the ISA recommended to adjust the pH for best
accuracy. Make sure that the samples and standards are at the same temperature. The glass
electrode sensing bulb will not be attacked by most organic solvents.
Units of Measurement
Sodium concentrations are measured in units of parts per million, equivalents per liter, moles per
liter, or any other convenient concentration unit. Table 1 indicates some of the concentration unit
conversion factors.