IEC 62021-1 Insulating liquids - Determination of acidity - Part 1: Automatic potentiometric titration
8 Preparation and maintenance of electrode system
Although electrodes are not particularly fragile they should be handled carefully at all times.
8.1 Preparation
Rinse the electrodes with 2-propanol and finally with de-ionized water.
Following each titration immerse the electrodes in de-ionized water to remove any surplus electrolyte adhering to the outside of the electrode and allow excess water to drain off. The immersion time should be sufficient to prevent any memory effects on subsequent titrations.
When in use, any plug that is present on the reference electrode should be removed and the electrolyte level in the electrode kept above that of liquid in the titration vessel to prevent entry of contaminants into the electrode.
8.2 Maintenance
8.2.1 Glass electrode
Clean the electrode weekly by immersing the tip in 0,1 mol/l hydrochloric acid for 12 h followed by washing with de-ionized water. If more aggressive cleaning is required, immerse the electrode tip in cleaning solution (see 5.7) for 5 min and follow this by thorough washing with de-ionized water. This treatment should be carried out on a monthly basis when the electrode is in regular use.
When not in use, immerse the lower half of the electrode in de-ionized water. Do not allow the electrode to dry out. If this occurs it may be possible to reactivate by immersing in cleaning solution (see 5.7) as detailed above.
8.2.2 Reference electrode
Drain and fill the electrode with potassium chloride electrolyte (see 5.5) at least once a week. When using the sleeve-type electrode, carefully remove the ground-glass sleeve and thoroughly wipe both ground-glass sleeve surfaces. Replace the sleeve loosely and allow a few drops of electrolyte to drain through to flush the ground-glass joint and to wet the ground surfaces thoroughly with electrolyte. Set the sleeve in place and refill with potassium chloride electrolyte (see 5.5).
When not in use, immerse the electrode in electrolyte (see 5.5) keeping the level of the electrolyte in the electrode above that of the immersion fluid level. The filling apertures should be covered during storage.
The electrode should be cleaned as necessary (at least weekly) by flushing with de-ionized water. Refill with potassium chloride electrolyte (see 5.5).
9 Calibration of apparatus
Determine the pH reading for the buffer solutions (see 5.6) on a daily basis. The value of the titration end-point of pH 11,5 is then extrapolated and must be entered into the instrumental programme.
The linearity and slope of the potentiometric titrator over the pH range 4 to 11 should comply with the electrode manufacturer's tolerances.
Temperature correction shall be applied.
NOTE Owing to the significant effect of temperature on the pH of the buffer solutions (see 5.6), it is desirable to keep the temperature as close to the buffer manufacturer's calibration temperature as possible.
