Tech Note 1066 Detail

ORP Probe Care

Affected Products:

CI-6716 Oxidation Reduction Potential Probe

Problem/Symptom:
Oxidation Reduction Potential Probe Care

PASCO Solution:

PREPARATION

  1. Remove the protective soaker bottle and rinse the bottom of the electrode with deionized water.
  2. Prior to first use or after long-term storage, immerse the electrode in deionized water for 30 minutes.

VALIDATION

  1. Set the probe to read in mV.
  2. Prepare enough pH 7.00 buffered water to completely immerse the membrane of the electrode.
  3. Add quinhydrone to saturate the buffered water. (Some crystals should be undissolved after stirring vigorously.)
  4. While stirring, immerse the electrode into the solution.
  5. Measure the potential after the reading stabilizes (30-60 seconds).
  6. The potential should be within +/- 20 mV of the standard values:
    Temperature [C] 20 25 30
    Standard Potential [mv] 92 86 79
  7. Remove electrode and rinse thoroughly with distilled water.
  8. Add sufficient crystals of quinhydrone to saturate a solution of 4.01 pH buffer.
  9. While stirring, immerse the electrode into the solution. (The measured voltage should respond rapidly.)
  10. Measure the potential after the reading stabilizes (30-60 seconds).
  11. The potential should be within +/- 20 mV of the standard values:
    Temperature [C] 20 25 30
    Standard Potential [mv] 268 263 213
  12. If the difference between the values of the electrode in the two buffers is less than 177 mV or the potentials are offset from the standard potentials by more than 20 mV, clean the electrodes.
  13. Rinse the electrode with distilled water.

STORAGE

Store in air or distilled water. If stored in air, rinse with distilled water

MAINTENANCE

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 1:10 dilution of household laundry bleach in a 0.1 - 0.5% liquid detergent solution in hot water with vigorous stirring for 15 minutes. Drain/refill the reference chamber. Soak the electrode in distilled water for at least 10 minutes.
  • Salt Deposits: Dissolve the deposit by immersing the electrode in 0.1 M HCl for five minutes, followed by immersion in 0.1M NaOH for five minutes, and thorough rinsing with distilled water.
  • Oil/Grease Films: Wash electrode in a little detergent and hot water. Rinse electrode tip with distilled water.
  • Clogged Reference Junction: Heat a diluted KCl solution to 60-80oC. Place the reference portion of the ORP 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 0.1M HCl for five minutes, followed by thorough rinsing with distilled water.

After any of these special cleaning procedures, remember to drain/refill the reference chamber, if refillable. Soak the electrode in storage solution for at least 10 minutes.

If these steps fail to restore normal electrode response, replace the electrode.

TROUBLESHOOTING

READINGS ARE NOT REPRODUCIBLE
  • Is there sample carryover?
  • Are there sample interferences or complexing agents present?
  • Is the reference electrode junction contaminated?
SLOW RESPONSE (READINGS SLOWLY CHANGING)
  • Was the electrode stored in the wrong solution?
  • Was the electrode poisoned by the sample?
OUT OF RANGE READING
  • Is the electrode plugged into the controller properly?
  • Is there a reference electrode present?
  • Is there enough fill solution left in the reference electrode?
  • Is the electrode placed in the sample solution?
LOW SLOPE OR NO SLOPE
  • Are the standards too old, contaminated, or made wrong?
  • Has the sample pH been adjusted properly to the operating range of the electrode?
  • Is there an air bubble on electrode surface?
  • Is the controller okay?
  • Is there enough fill solution left in the reference electrode?
NOISY RESPONSE (READINGS RANDOMLY CHANGING)
  • Is the controller grounded?
  • Is there an air bubble on electrode surface?
  • Is the controller operating properly?
  • Is there enough fill solution left in the reference electrode?
DRIFTY RESPONSE (READINGS CONTINUOUSLY CHANGING)
  • Is there excessive leaking at the reference electrode junction?
  • Is the reference electrode junction clogged?
  • Was the sensing membrane poisoned by the sample?
  • Are there temperature problems?
  • Is the sample too concentrated?
  • Does the sensing membrane need conditioning?
INACCURATE READINGS (BUT CALIBRATION IS OK)
  • Are the standards incorrect?
  • Was the sample pH adjusted properly?
  • Is there sample carryover?
  • Are there sample interferences or complexing agents present?

Creation Date: 02/18/2010
Last Modified:
Mod Summary: