ORP Sensor

All user manuals come with the necessary information about the short and long term storage of the respective probe.

General tips for long term storage:

ORP electrodes should be stored in the wetting cap filled with reference electrolyte (often 3 mol/L KCl).

Several factors can lead to the blockage of ORP sensor diaphragms. In particular, junctions made of ceramic, or other porous material are prone to clogging. The most frequent reasons are listed here together with the respective cleaning procedures:

Blockage with silver sulfide (Ag₂S): if the reference electrolyte contains silver ions and the sample being measured contains sulfides, the junction will get contaminated with a silver sulfide precipitate. To clear the junction of this contamination, clean it with 8% thiourea in 0.1 mol/L HCl solution (Thiourea Cleaner is available from METTLER TOLEDO).

Blockage with silver chloride (AgCl): the silver ions from the reference electrolyte can also react with samples that contain chloride ions, resulting in an AgCl precipitate. This precipitate can be removed by soaking the electrode in a concentrated ammonia solution (35% NH₃ aq.).

Blockage with proteins: junctions contaminated with proteins can often be cleaned by immersing the electrode in a pepsin/HCl (5 % pepsin in 0.1 mol/L HCl) solution for several hours (Pepsin-HCl Cleaner is available from METTLER TOLEDO).

Other junction blockages

If the junction is blocked with other contaminations, try cleaning the ORP sensor in an ultrasonic bath with water or with a 0.1 mol/L HCl solution.

Redox electrodes with a platinum ring are the "standard" ORP sensors. This is why we have it with different geometries and junctions (e.g. InLab^® Redox Micro, InLab^® Redox Pro). Redox electrodes are only used if anything in the sample undergoes a chemical reaction with platinum -- the idea behind the noble metal ring is to not be involved in any chemical reaction. One example where a platinum redox electrode is not recommended is concentrated hydrochloric acid because Pt-Clcomplexes can be produced.