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PROBEST PINH3-900 and PISE ammonia-nitrogen (NH₄⁺-N) ion-selective electrodes are widely used in water quality monitoring, wastewater treatment, environmental testing, and industrial process analysis. In daily operation, common issues such as drifting readings, unstable values, slow response, and inconsistent measurement results are mostly caused by deteriorated, depleted, contaminated, or air-bubble trapped internal electrolyte. Properly replacing the NH₄N electrolyte is the most effective and economical way to restore electrode performance, ensure measurement accuracy, and extend service life.
This article provides a complete technical tutorial for troubleshooting inaccurate probe readings and performing standard electrolyte replacement for PROBEST PINH3-900 and PISE electrodes.
Your PROBEST ammonia-nitrogen electrode may require electrolyte inspection or replacement if you observe:
Continuous drifting that cannot stabilize
Consistent high or low bias compared to standard solutions
Significantly slow response and long equilibrium time
Unstable signal, fluctuation, or electrical noise
Calibration failure or electrode slope out of the acceptable range (typically 95%–105%)
Visible contamination, crystallization, or air bubbles inside the electrode
Electrolyte volatilization, concentration change, or contamination
Fouling, aging, or damage of the gas-permeable membrane
Air bubbles trapped near the sensitive membrane
Dehydration due to improper dry storage
Interference from suspended solids, oil, or high salinity in samples
Original PROBEST specified NH₄N internal electrolyte
Distilled or deionized water
Lint-free cleaning wipes
Small screwdriver (for certain models)
Syringe or dropper for clean filling
Ammonia-nitrogen standard solutions for calibration
Power off the meter and disconnect the electrode before maintenance
Do not touch or scratch the sensitive ion-selective membrane
Maintain a clean environment to avoid secondary contamination
Dispose of used electrolyte according to local waste regulations
Remove the protective cap and take the electrode out of the holder or meter
Open the filling port cap or screw seal (PINH3-900 / PISE structure)
Carefully unscrew the membrane cap at the tip; keep all gaskets and small parts
Pour out all old, exhausted electrolyte completely
Gently rinse the inner cavity and membrane cap with distilled water 2–3 times
Shake lightly to remove residual liquid; do not strike forcefully
Wipe the electrode body clean
Hold the electrode at a 45° angle to prevent air bubbles
Slowly inject fresh electrolyte up to the marked level or filling port
Tap the electrode body lightly to release trapped air bubbles
Ensure no bubbles remain near the sensitive membrane
Clean any spilled electrolyte from the surface
Reinstall O-rings and membrane cap; tighten securely to prevent leakage
Close the filling port cap
Place the reassembled electrode into ammonia-nitrogen standard solution
Allow polarization for 10–30 minutes (per PROBEST specification)
Do not calibrate or measure until the signal is fully stable
Rinse the electrode with distilled water and blot dry
Perform calibration with at least two standard solutions for PINH3-900 / PISE
Check the electrode slope; valid slope confirms successful replacement
Measure a quality control sample to verify accuracy
If problems continue, check for membrane fouling, air bubbles, or leakage
Symptom | Possible Cause | Solution |
|---|---|---|
Drifting readings | Low electrolyte level or air bubbles | Refill to correct level; remove bubbles |
Large measurement bias | Expired electrolyte or fouled membrane | Replace electrolyte; clean or replace membrane |
Unstable signal | Poor sealing or clogged junction | Check O-rings; clean liquid junction |
Very slow response | Insufficient polarization | Extend activation time |
Calibration failed | Non-original electrolyte used | Use only PROBEST specified NH₄N electrolyte |
Replace internal electrolyte every 1–3 months or when performance declines
After use, rinse with distilled water and store in recommended solution
Do not leave the electrode dry or in deionized water for long periods
Increase cleaning frequency for high-fouling wastewater samples
Calibrate before critical measurements
Maintain maintenance logs: replacement date, slope, calibration results
Inaccurate, drifting, or unstable readings of PROBEST PINH3-900 and PISE ammonia-nitrogen electrodes can most often be resolved by replacing the NH₄N internal electrolyte. Following this standard tutorial will quickly restore accuracy, reduce downtime, and lower operating costs.
Always refer to the official PROBEST electrode manual for specific filling volume and polarization time. For further technical support, please contact our service team.