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pH Electrode Care and Maintenance
pH electrode is the most sensitive component of pH instrumentation. 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. 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 the pH system includes calibration buffers for a range of pH buffer values used.
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. Always rinse electrodes with distilled or de-ionised water before and after measuring a sample. Shake off excess liquid gently to dislodge droplets and blot dry its housing suffices before dipping into test sample or fresh buffer. NEVER wipe the electrode glass bulb with paper towel as wiping can create electrostatic 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. NEVER soak or keep electrode in distilled water or de-ionised water for long period as long term exposure to pure water will damage the special glass membrane. After conditioning the sensor, rinse the electrode with distilled or de-ionised water. The electrode is ready for calibration and measurement.
Storing
The sensor should never be stored dry. Best to keep pH electrode moist at all times. 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. DO NOT store electrode in stoage bottle filled with distilled or de-ionised water - this will cause ions to leach out of the glass bulb and render 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 with water 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 0.1 M HCl 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 distilled or e-ionised water. Drain used and replenish with fresh reference fill solution if necessary before use.
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