Hach-Lange POLYMETRON 8350_8351 User Manual - Manual (Page 9)

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4 CALIBRATION
Before calibrating for the first time:
• Shake the probe gently to remove any air bubbles from underneath the glass bulb.
• Remove the storage cap and rinse the probe with demineralised water.
4.1 pH
Refer to the pH transmitter's instructions to select the correct calibration type.
• Rinse the probe with the freshly prepared first buffer solution (pH 6.88 or 7.00), ideally at
the temperature of the sample to be measured.
• Immerse the probe (to a depth of 4 to 5cm) and wait for stable measurements before
calibrating.
• Rinse the probe, first with demineralised water and then with the second buffer solution
(pH close to that of the process, 4.00 or 9.22).
• Immerse the probe (to a depth of 4 to 5cm) and wait for stable measurements before
calibrating.
• Rinse the probe in demineralised water.
4.2 REDOX
• Rinse the probe using a standard, freshly prepared quinhydrone solution, ideally at the
temperature of the sample to be measured.
• Immerse the probe (to a depth of 4 to 5cm) and wait for stable measurements before
calibrating.
The potential is measured with respect to the Ag/AgCl reference system. Add 200mV for an
E
H2
reference potential.
5 CLEANING AND RECONDITIONING
These electrodes are considered as consumable items and therefore have a limited lifespan,
largely dependant on the user's application. Under normal conditions, a typical lifespan would be
about one year.
Before replacing them, however, simply cleaning the electrodes may restore them.
Such cleaning will also be necessary whenever the following are observed:
• An offset from zero or a measurement drift (the reference system is contaminated).
• A significant drop in response time and a loss of slope (there is fouling on the glass diaphragm
or the platinum).
Provided the glass diaphragm is neither scratched nor cracked, follow one of the cleaning
procedures below:
• Salt deposits: HCl 0.1M (5 mins) + NaOH 0.1M (5 mins)
• Grease or oil film: Detergent + water
• Reference junction fouled: KCl 3M @ 60-80 °C for 10 mins, then cool in KCl 3M@25 °C
• Calcium, metal hydroxide or protein deposits: HCl 10% for 10 mins
• Redox measurements:
• Deposits/ wear: aqua regia (1/1 concentrated HCl / concentrated HNO
3
); this process must
only be carried out by qualified individuals.
If the electrode's response is not improved, replace it.