Electrodes Direct

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GENERAL TROUBLESHOOTING (pH, ORP, ISE, etc.)

The goal of troubleshooting is the isolation of a problem through checking each of the system components in turn: the meter, the glassware, the electrode, the standards, the sample, and the technique.

Meter

The meter may be checked by following the checkout procedure in the instrument instruction manual.

Glassware

Clean glassware is essential for good measurement. Be sure to wash the glassware well with a mild detergent and rinse very well with distilled or deionized water. Clean glassware will drain without leaving water droplets behind.

Electrodes

The electrodes may be checked by performing an electrode calibration.
1. Be sure to use distilled or deionized water when performing a calibration.
2. If the electrode fails to respond as expected, see the section entitled Maintenance (see column to left). Repeat the calibration.
3. If the electrode still fails to respond as expected, substitute another electrode that is known to be in good working order for the questionable electrode. If the problem persists and you are using an electrode pair, try the same routine with a working reference electrode.
4. If the problem persists, the standards may be of poor quality. Open fresh standards and attempt to calibrate the electrode again.
5. If another electrode is not available for test purposes, or if the electrode in use is suspect, review the calibration procedure and be sure to:
* Clean and rinse the electrode thoroughly.
* Prepare the electrode properly.
* Use the proper filling solution.
* Review TROUBLESHOOTING HINTS (below).

Standards

Whenever problems arise with the measuring procedure that has been used successfully in the past, be sure to check the standard solutions. If in doubt about the credibility of any of the standards, open fresh standards.

Sample

Look for possible contaminants if the electrode works perfectly in the standard, but not in the sample. Try to determine the composition of the samples prior to testing to eliminate a problem before it starts.

Technique

Be sure that the electrode's limit of detection has not been exceeded. Be sure that the calibration procedure is clearly understood and that Good Laboratory Practice has been followed.

TROUBLESHOOTING HINTS

Symptom Possible Causes Next Step


Out of Range Reading



defective meter
defective electrode
electrode(s) not plugged in properly
reference electrode not filled
air bubble on membrane
calibration control not turned far enough
check meter with shorting strap (see meter instruction manual)
check electrode operation
unplug electrode(s) and reseat
be sure reference electrode is filled
remove bubble by redipping electrode
continue turning the calibration control
Noisy or Unstable Readings  defective meter
air bubble on membrane
wrong reference electrode
meter or stirrer not grounded
check meter with shorting strap
remove bubble by redipping electrode
use the recommended reference electrode
ground meter or stirrer
Readings Drift samples and standards at different temperatures 
incorrect reference filling solution
allow solutions to come to room temperature before measurement 
use recommended filling solution
Low Slope or No Slope standards contaminated or incorrectly made use fresh standards


ADDITIONAL TROUBLESHOOTING QUESTIONS

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 Changin)

- 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 (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?

ADDITIONAL ION SELECTIVE ELECTRODE TROUBLESHOOTING QUESTIONS

- Have you checked the electrode slope?
- Are you using fresh standards for calibration?
- Are there any solution air bubbles on membrane surface?
- Are you measuring only aqueous or near-aqueous samples?
- Are you operating at a constant pressure?
- Are you operating at a constant temperature?
- Have you adjusted the pH of samples to ISE operating range if necessary?

CONDUCTIVITY TROUBLESHOOTING QUESTIONS

- Have you selected the correct electrode Cell Constant for your sample?:

Cell Constant Kccm-1 Optimum Conductivity Range, uS/cm
0.01 0.055 to 20
0.1 0.5 to 200
1.0 10 to 2,000
10 100 to 20,000
100 1,000 to 200,000
Electrodeless 500 to 106

- Have you selected the proper range on your meter/monitor?
- Does your electrode have the proper materials for corrosion resistance?
- Have you checked for air bubbles on the sensor?
- Have you checked the sensor for fouling (buildup)?
- Is your sample at a constant temperature, and if not, are you using a temperature compensator to correct for temperature fluctuations?

DISSOLVED OXYGEN ELECTRODES

SYMPTOM POSSIBLE CAUSE RECOMMENDATION
Slow/Sluggish Response
membrane is coated/fouled
anode/cathode require rejuvenation
electrolyte expired
clean membrane
perform anode/cathode cleaning (see manual)
replace electrolyte
No Response/Erratic Response
broken membrane
membrane not seated
defective meter/monitor
replace membrane
inspect, replace or adjust membrane
check meter/monitor
Erroneous Readings improper calibration
bad standards
temperature compensator bad
other
re-calibrate meter
make new standards, recalibrate
check temp. comp. or order new probe
verify pressure, salinity (compensated?),altitude (compensated?)

 

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