Troubleshooting: what is wrong with my electrode?

Question: What are you observing in your measurement?

• The reading takes a very long time to settle
• Calibration fails or is rejected
• The reading slowly wanders off (drift)
• The reading jumps around restlessly
• The reading is constant but implausible

Question: How long was the electrode dry or unused recently?

• It lay dry or unused for weeks
• It was stored moist throughout

Question: Is the junction visibly coated or discoloured, or was the electrode in a demanding medium?

• Yes - deposits, discolouration, proteins or fat involved
• No - everything looks clean

Question: How old are the buffer solutions you used?

• Opened, older than six months or unknown
• Freshly opened and within the expiry date

Question: What does the meter report after calibration?

• Slope too low (below about 90 %)
• Zero point far off (outside ±30 mV)
• No reaction at all, the value stays put

Question: Does the temperature of sample or surroundings change noticeably during that time?

• Yes, the temperature fluctuates
• No, the temperature is stable

Question: Is it a refillable electrode with liquid electrolyte?

• Yes, refillable
• No, gel or polymer electrode

Question: Does the reading calm down when you briefly switch off pumps, heaters or other devices?

• Yes, then it becomes calmer
• No, no change

Question: Are there air bubbles on the membrane, or is the sample very low in ions (ultrapure, reverse-osmosis or distilled water)?

• Air bubbles or too little movement in the medium
• Very low-ion water
• Neither

Question: Is the displayed value in the strongly alkaline range, roughly above pH 12?

• Yes, strongly alkaline sample
• No, normal measuring range

Question: In mV mode, does the meter show a value close to 0 mV in fresh pH 7 buffer?

• Yes, close to 0 mV - then the electrode is not the cause
• No, far off

Likely cause: The hydrated layer needs to rebuild first

An electrode stored dry measures sluggishly because the water-containing layer on the glass membrane is missing. This is often repairable.

1. Soak for 24 hours in KCl storage solution
2. Then recalibrate and read the slope
3. Slope back above 95 %? Electrode saved
4. If it stays below, the hydrated layer is permanently damaged

Read in detail: Storing correctly

Likely cause: Junction or membrane are fouled

Fouling is the most common cause of sluggish and drifting readings - and the easiest to fix. Important: dissolve, do not scrub.

1. Identify the contamination: limescale, protein, fat or sulphide
2. Choose the matching cleaner - never rub mechanically
3. Then soak for several hours in KCl solution
4. Recalibrate - only then can success be judged

Read in detail: Cleaning & care

Likely cause: The electrode is nearing the end of its life

A persistently low slope after cleaning and soaking means the glass membrane has served its time. Three rescue attempts are still worthwhile; after that, replacement is the more economical decision.

1. Clean thoroughly and soak for several hours
2. On refillable electrodes, renew the electrolyte completely
3. Regenerate: briefly in dilute hydrochloric acid, then soak at length
4. If the slope stays below 90 %, replace the electrode

Read in detail: Lifespan & faults Buying guide

Likely cause: The reference system is disturbed

A widely shifted zero point points to a clogged junction or exhausted or contaminated electrolyte - less often to the glass membrane itself.

1. Soak the junction in warm KCl solution (not above 50 °C)
2. On a sleeve junction, loosen the ring and slide it under water
3. On refillable electrodes, exchange the electrolyte completely
4. Recalibrate and check the zero point again

Read in detail: Cleaning & care

Likely cause: The buffer solutions are the likely cause

Buffers age - alkaline ones in particular absorb CO₂ from the air and shift measurably. Calibrate with a degraded buffer and everything measured afterwards is wrong.

1. Use fresh pH 7 and pH 4 buffers, check the expiry date
2. Always decant into clean beakers, never measure from the stock bottle
3. Discard used buffer, never pour it back
4. Rinse thoroughly with distilled water between buffers

Read in detail: Calibrating correctly

Likely cause: It is a temperature effect, not a fault

The voltage per pH unit depends on temperature - about 59 mV at 25 °C, already about 66 mV at 60 °C. Without compensation the reading wanders with the temperature.

1. Activate temperature compensation on the meter (ATC)
2. Without ATC: bring sample and buffers to the same temperature
3. Before reading, wait until the electrode has reached the sample temperature

Read in detail: Basics of measurement

Likely cause: Check the fill level and refill opening

On refillable electrodes, a closed refill opening is the classic: without electrolyte flow the junction fouls and the reading drifts.

1. Open the refill opening during measurement
2. Keep the fill level well above the sample level
3. Top up or completely renew the electrolyte
4. Close the opening again after measuring

Read in detail: Liquid-electrolyte electrodes

Likely cause: Electrical interference is disturbing the measurement

The electrode signal is high-impedance and therefore sensitive to interference - pumps, heaters, fluorescent tubes and damp connectors are typical culprits.

1. Route the electrode cable separately from mains cables
2. Check the connector for moisture and dry it
3. For long cable runs, use a transmitter or digital sensor
4. If possible, move the source of interference to a different circuit

Read in detail: Process measurement

Likely cause: Air bubbles or too little movement

An air bubble on the membrane interrupts contact with the sample; standing liquid delays equilibration. Both are fixed in seconds.

1. Swing the electrode briefly to detach bubbles
2. Shake bubbles in the inner buffer upwards carefully
3. Move or stir the sample gently - but not too vigorously
4. Immerse the membrane fully, including the junction

Likely cause: Low-ion water needs a special electrode

The purer the water, the harder the measurement: low-ion water conducts poorly and the signal becomes unstable. This is not a fault but a question of the right electrode.

1. Choose an electrode with increased electrolyte outflow
2. Use a flow-through fitting instead of beaker measurement
3. Minimise contact with air - dissolved CO₂ falsifies further

Read in detail: Water treatment

Likely cause: Probably alkaline error

In strongly alkaline solutions, sodium ions fake a pH that is too low to the glass membrane. Standard glass is simply at the end of its range there.

1. Use an electrode with low-alkaline-error special glass
2. Calibrate with pH 7 and pH 10 instead of pH 7 and pH 4
3. Keep the measuring temperature low - heat amplifies the effect

Read in detail: Glass electrode & special glasses

Likely cause: Check cable, connector and meter

If the display does not react at all, the electrode is often not to blame: a damp or dirty connector, a cable break or a faulty meter input produce the same picture.

1. Unplug, dry and visually inspect the contacts
2. Check the cable for kinks and breaks
3. If possible, cross-test with a second electrode
4. If the second electrode also fails to react, the meter is the cause

Likely cause: The electrode is working - check meter and procedure

If the electrode delivers a plausible value in mV mode, it is fine. It is then worth looking at calibration settings, buffer recognition and sample preparation.

1. Reset the meter's calibration and repeat it
2. Check the buffer set in the meter (NIST, DIN or technical buffers)
3. Check the sample for homogeneity and temperature

Read in detail: Calibrating correctly