EIJKELKAMP 18.50.01 Bedienungsanleitung Seite 134

MAINTENANCE, TIPS & THEORY
pH ELECTRODE CARE & MAINTENANCE
Your pH electrode is the most sensitive component of your pH instrument. Correct calibration
procedures combined with proper maintenance will provide years of reliable measurement.
Calibration
Since glass pH electrodes measure H+ (hydrogen ion) concentration relative to their reference half-
cells, they must be calibrated periodically to ensure accurate, repeatable measurements. Our wide
selection of commercial pH calibration buffer sachets include solutions that are standardized against
NISTcertified pH references for calibrating meters with resolution up to 0.01pH. Although calibration
against one pH reference buffer (one-point calibration) typically ensures accurate pH measurement,
frequent two-point or even three-point calibrations ensure the most reliable results. Make sure your pH
system includes calibration buffers for a range of pH values.
Handling
During shipment it is possible for air bubbles to move into the glass bulb. To remove air bubbles,
shake down the electrode in the same manner as a clinical thermometer until the glass bulb is filled
with solution.
Rinse electrodes with distilled water before and after measuring a sample. Blot the end of the
electrode with lint-free paper to remove excess water. NOTE: Never wipe the electrode to remove
excess water - wiping can create static charges that interfere with correct pH measurement.
Conditioning
After removing the electrode from soaking bottle or protective cap at the bottom of sensor, place the
electrode in a clean container containing one of the liquids i.e. 4.0 M KCl or pH 7.0 buffer. Soak
electrode for 30 minutes if left dry. NOTE: Never condition the electrode in distilled water or deionised
water - long term exposure to pure water will damage the special glass membrane. After conditioning
the sensor, rinse the electrode with distilled or deionised water. The electrode is ready for calibration
and measurement.
Storing
The sensor should never be stored dry. Always keep pH electrode moist. Proper pH electrode storage
maximizes electrode performance and extends electrode life. It is best to store electrodes in clean
containers filled with pH storage solution, EC-RE005. Do not store an electrode in distilled or
deionised water - this will cause ions to leach out of the glass bulb and render your electrode useless.
Cleaning
The solution used to clean pH electrode depends on the presence of possible contaminants.
Mechanically intact electrodes may show slow response due to coating or clogging. Use the guide
below to choose the appropriate cleaning solution options:-
•
For general cleaning: Soak the pH electrode in 0.1 M HCl or 0.1 M HNO3 for 20 minutes. Rinse
well in tap water before use.
•
For removing stubborn deposits and bacteria: Soak the pH electrode in a 1:10 dilution of
household laundry bleach for 10 minutes. Rinse thoroughly before use.
•
For removal of oil and grease: Rinse the pH electrode in mild detergent or methyl alcohol. Wash
in water before use.
•
For removal of protein deposits: Soak the pH electrode in 1% pepsin in 0.1m HCl (EC-DPC-BT)
for 5 minutes. Rinse well in water before use.
CAUTION: Proper eyewear and hand gloves must be used when handling strong chemicals.
After any of the cleaning procedures, it is good practice to thoroughly rinse the pH electrode with
deionised water, drain and refill the reference chamber if necessary before use.
CONDUCTIVITY THEORY
Conductance is a quantity associated with the ability of primarily aqueous solutions to carry an
electrical current, I, between two metallic electrodes when a voltage E is connected to them. Though
water itself is a rather poor conductor of electricity, the presence of ions in the water increases its
conductance considerably, the current being carried by the migration of the dissolved ions. This is a
clear distinction from the conduction of current through metal, which results from electron transport.
The conductance of a solution is proportional to and a good, though nonspecific indicator of the
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