How should pH and conductivity electrodes be cleaned?

Document ID

Document ID TE2707

Published Date

Published Date 11/06/2018
Question
How should pH and conductivity electrodes be cleaned?
Summary
pH and conductivity electrode cleaning
Answer
The best cleaning solution for an electrode depends on the type of contamination.

Common symptoms of a probe in need of cleaning:
  1. Slow response
  2. High assymetry potential/Slope out of range
  3. Poor sensitivity/drifting, inaccurate readings
 
pH probe cleaning recommendations
Contaminants Use Description Comments
Fats, Oils, and Grease Most common contaminants for water treatment applications (municipal and industrial markets) 1. Soak in  Electrode Cleaning Solution  (Catalog Number/Order Code 2965249) for at least 2 hours or overnight.
2. Ethanol, 95% (Catalog Number/Order Code 2378900
1. All Hach pH electrodes
2. Ideal for glass and epoxy bodies only
Limescale/Mineral Buildup For the dissolution of mineral deposits, lime, and scale.
Soak in HYDROCHLORIC ACID, 0.1N 1000ML (Catalog Number/Order Code 1481253) for no more than 5 minutes
All Hach pH electrodes
Proteins For the regeneration of electrodes that usually measure samples with a high protein content, such as milk, cheese, meat, blood, or serum. 1. Probe Cleaning Solution for Samples that Contain Proteins, 500 mL (Catalog Number/Order Code 2964349)
2. NaOH (2%)
All Hach pH electrodes
Sulfides
(Ag+ precipitation across junction)
 
Black deposits appear on the junction when an electrode is used with an Ag/AgCI wire reference in samples containing sulfides, or reducing substances, The silver salts which are formed are dissolved in the thiourea solution. Prepare 1 M Thiourea in 0.1 M HCl: Mix 76.12 g of THIOUREA, >99.0% (Catalog Number/Order Code 1123100) into 1L of Hydrochloric Acid Standard Solution, 0.10 N, 1 L (Catalog Number/Order Code 1481253) and stir slowly to dissolve. Ideal for glass and epoxy bodies only; preparation required.
General
 
Common solution for most types of contamination 1. Hydrochloric Acid Standard Solution, 0.10 N, 1 L (Catalog Number/Order Code 1481253)
2. Dilute bleach solution: 1 part SODIUM HYPOCHLORITE, >10% AR (Catalog Number/Order Code 2602100) to 10 parts deionized water.
1. All Hach pH electrodes
2. Ideal for glass and epoxy bodies only; dilution required.
Conductivity probe cleaning recommendations
Fats, Oils and Grease Most common contaminants for water treatment applications (municipal and industrial markets) 1. Soak in  Electrode Cleaning Solution  (Catalog Number/Order Code 2965249) for at least 2 hours or overnight.
2. Ethanol, 95% (Catalog Number/Order Code 2378900
Suitable for all Hach EC cells
Limescale/Mineral Buildup For the dissolution of mineral deposits, lime, and scale Soak in HYDROCHLORIC ACID, 0.1N 1000ML (Catalog Number/Order Code 1481253) for no more than 5 minutes Suitable for all Hach EC cells
 


For additional pH cleaning recommendations, the pH Electrode Cleaning and Maintenance Guide is useful.