Cleaning the Sensor of an Ammonia-N Autoanalyzer

The sensor is the core component of an online ammonia‑nitrogen (NH₃‑N) autoanalyzer. Its surface condition directly determines the accuracy and reliability of the measurement data. During prolonged immersion in water samples, the sensor inevitably accumulates fouling from suspended solids, organic residues, biofilms, and salt crystals.

 If not removed promptly, these deposits cause sluggish electrode response, signal drift, and eventually permanent damage to the sensitive membrane. A systematic, well‑defined cleaning procedure is therefore essential for maintaining instrument stability and extending electrode service life. Sensor cleaning should follow the principle of physical cleaning first, chemical cleaning second, and graded treatment according to the degree of contamination. Before any cleaning operation, power off the instrument and carefully remove the sensor from the flow cell.

Physical Cleaning

Physical cleaning is suitable for lightly contaminated sensors where loose deposits are present on the surface. A soft brush is dipped in deionised or distilled water at room temperature and used to gently wipe the sensing surface and the membrane area in a single direction. 

This removes attached suspended impurities and light organic residues. During this process, avoid applying excessive force or using hard tools, as these can scratch the sensitive membrane. After brushing, rinse the sensor thoroughly with deionised water to ensure no debris remains. For instruments in continuous operation, a daily routine of wiping the membrane surface gently with a soft cloth soaked in pure water helps prevent the build‑up of visible contaminants.

Chemical Cleaning

When the sensor surface is covered with stubborn contamination such as biofilms, calcium‑magnesium scale, or grease, physical cleaning alone is insufficient. Chemical immersion is required. The sensor is immersed in a dedicated cleaning solution for 5 to 10 minutes, allowing the solution to dissolve the tenacious deposits. 

Commonly used cleaning agents include dilute hydrochloric acid at a concentration of approximately 10 %, weak acidic descaling agents, or neutral detergents. If the monitored water contains high levels of organic matter or algae, the cleaning interval should be shortened, and a neutral cleaning solution recommended in the instrument manual should be used.

For sensors employing ion‑selective electrodes, a weekly activation treatment is recommended. This involves soaking the electrode in a standard ammonia‑nitrogen solution for about 2 hours to restore its ion‑response sensitivity. After activation, the electrode must be rinsed with distilled water before being returned to service.