pH Electrode Best Practices - Van London

BEST PRACTICES & RECOMMENDED HANDLING, QC and CLEANING FOR pH ELECTRODES

Q.C. PROCEDURE

Switch the pH/mV meter to the mV mode. This can also be accomplished by changing the measurement setting from pH to ORP.
Fill 3 beakers with the distilled water 7.00 buffer and 4.01 buffer. The temperature of the solutions should be close to 25°C.
Place the electrode into the pH 7.00 buffer solution, manually swirl the probes, and allow 20 seconds to stabilize and record the mV value. This is the "E₀" or offset reading. Electrode drifting after one minute should be noted.
Remove the electrodes from the 7.00 buffer, rinse thoroughly with deionized water.
Place the electrode into the 4.01 buffer solution, manually swirl the probes, and allow 20 seconds to stabilize and record the mV value.
Calculate the electrode slope by calculating the difference between the 7.00 buffer mV reading and the 4.01 buffer mV reading. Record the difference as slope.

Specification limits for a new electrode are as follows:

E₀ -30 to +30 mV

Slope 169.0 to 180.0

ELECTRODE CLEANING
Electrodes which are mechanically intact with no broken parts can often be restored to normal performance by one of the following procedures:

General Cleaning: Soak the electrode in 10% dilution of household laundry bleach with liquid detergent solution in hot water with vigorous stirring for 15 minutes. Rinse with warm, running tap water for 15 seconds.
Heavy Metal Coating: Soak the electrode in a 10% dilution of acetic acid and water with vigorous stirring for 15 minutes. Then rinse with distilled water.
Salt Deposits: Dissolve the deposit by immersing the electrode in 10% HCl for five minutes, followed by immersion in 10% NaOH for five minutes, and thorough rinsing with distilled water.
Oil/Grease Films: Wash electrode pH bulb in a little detergent and water. Alcohol or Acetone can also be used. Rinse electrode tip with distilled water.
Clogged Reference Junction: Heat a diluted KCl solution to 60-80oC. Place the electrode into the heated KCl solution for approximately 10 minutes. Allow the electrode to cool while immersed in some unheated KCl solution.
Protein Deposits: Dissolve the deposit by immersing the electrode in a 1% pepsin solution with a background of 10% HC1 for five minutes, followed by thorough rinsing with distilled water.

After any of these special cleaning procedures, remember to soak the electrode in 4.01 buffer solution for at least 10 minutes. If these steps fail to restore normal electrode response, replace the electrode.