pH Sensor Cleaning - Practical Service Guide – Kuntze Instruments GmbH

ZIRKON® pH Sensor Cleaning Procedure

Clean your ZIRKON® pH sensor by hand before calibration, after visible fouling, or when measurement drift appears. This guide follows the official cleaning video and covers diaphragm treatment, pH glass care, and KCl regeneration of the gel layer.

Applies to: ZIRKON® pH sensors used with NEON® ONE, KRYPTON® ONE, and legacy Kuntze analyzers. Always use chemicals approved for your site and sensor type.

Video tutorial

Step-by-step cleaning of the diaphragm and pH glass, including regeneration in KCl solution:

Direct link: https://youtu.be/9MmNSA4VZFE

When cleaning is needed

Measured value is unstable or drifts
Sensor response is slow
Calibration slope or offset is out of the expected range
Visible deposits on the glass bulb, diaphragm, or junction
Before first installation after storage, service, or replacement

Important: Sensors must be cleaned by hand before being inserted into the flow cell or calibrated. Do not calibrate a dirty sensor.

Preparation

Wear suitable PPE for the cleaning chemicals you use
Gather supplies:
- Soft, lint-free tissue or paper towel
- Clean water for rinsing
- Approved cleaning solution or dilute hydrochloric acid (for example 10% HCl) as shown in the video
- KCl storage solution (for example 3M KCl) for regeneration
- If contamination persists: diamond file (diaphragm only) and alcohol (organic films on the glass)
Handle the sensor carefully—the glass bulb is sensitive
Remove the sensor from the assembly and disconnect the cable when required for safe access

Standard cleaning procedure (video sequence)

Initial soak: Place the sensor briefly in the cleaning solution (approved cleaner or dilute HCl as permitted for your application). Remove after a few moments.
Optional regeneration: If recommended for your sensor, place it in KCl solution to support the reference and gel layer.
Wipe once: Gently wipe the sensor once with a soft, lint-free tissue. Do not rub or polish the pH glass.
Stubborn diaphragm fouling: If contamination remains on the diaphragm, use a diamond file and move it across the diaphragm surface— never lengthwise, to avoid damaging the pH glass. This opens the diaphragm and can remove limescale, rust, and dirt. A black diaphragm can indicate offset or a high zero point.
pH glass: The pH glass must not be cleaned mechanically (no abrasives, files, or scrubbing on the bulb).
Oily or organic films on the glass: Use alcohol only as needed for grease or fat. Alcohol attacks the gel layer—follow immediately with a KCl soak for several minutes or longer to regenerate the sensor.
Finish: Rinse thoroughly with clean water, or gently blot excess KCl with a soft tissue. Do not rub the glass bulb dry.
Reinstall: Return the sensor to the flow cell and allow stabilization before calibration.

Cleaning by fouling type

Fouling type	Approach (see video)
General deposits	Brief soak in approved cleaning solution; gentle single wipe; rinse with water
Limescale, rust, inorganic deposits on diaphragm	Initial clean as above; if needed, diamond file across the diaphragm only (not on glass)
Oily or organic contamination on glass	Alcohol on the pH glass, then KCl regeneration soak, then water rinse
Protein or biological fouling	Approved enzymatic cleaner if specified for your site—rinse thoroughly, regenerate in KCl if required, then calibrate

Always follow your approved service chemicals, concentrations, and exposure times. When in doubt, contact Kuntze support before using aggressive chemistry.

Important do / do not

Do:

Rinse between steps and after final cleaning
Regenerate in KCl after alcohol cleaning or when the gel layer may be affected
Calibrate after cleaning once the sensor has stabilized
Use the diamond file only on the diaphragm, moving across the surface

Do not:

Polish, scratch, or mechanically abrade the pH glass bulb
Use unapproved aggressive chemicals
Let the pH sensor dry out during storage—use KCl-filled protective caps
File or scrape the diaphragm lengthwise (risk of damage to the glass)

After cleaning

Check signal stability in the process or in buffer before accepting calibration
Perform pH calibration (recommended: 2-point with suitable buffers, for example pH 7 and pH 4)
Rinse the probe with water and pat dry between buffer solutions to avoid cross-contamination
If performance is still poor after a correct cleaning and calibration, repeat cleaning or replace the sensor