20 Feb

Electrodes

How do you know which pH electrode is right for your pH measurement application?  Many manufacturers have guides which show which pH probe is best for an environment or application.  Here are some applications and types of electrodes:

Biological/Pharmaceutical:  TRIS buffer, proteins, enzymes – Calomel (Hg2Cl2) free or double junction

Education/Student Use – Epoxy body for durability

Emulsions:  Petroleum products, paint – Open junction electrodes (to prevent clogging)

Flat Surfaces:  Cheese, meat, agar – Flat surface and double junction(no contact of  Ag with food)

Flat Surfaces:  Paper – Flat surface tip

General Purpose:  Most sample types – Most pH electrodes will work in general purpose applications

Harsh Environments:  Field or plant use, rugged use - Epoxy body and Gel filled

High Ionic Strength:  Acids, bases, brines, pH > 12 or pH < 2 – Open junction

Large Sample Sizes:  Tall flasks – Long body electrodes

Low Ionic Strength:  Treated effluent, deionized water, distilled water – Refillable (better contact with the sample)

Nonaqueous:  Solvents, alcohols – Glass body and Open junction

Semi-solids:  Fruit, meat, cheese – Spear tip with Open junction Ag/AgCl reference

Small Sample Size:  Micro-titer plates, NMR tubes, test tubes, small flasks – Small diameter electrode

Small Sample Size:  TRIS buffer, proteins, sulfides – Small diameter and Calomel free or Double junction

Titration:  Open junction

Viscous Liquids:  Slurries, suspended solids sludges – Open junction

Waters – Acid rain, boiler feed water, distilled water, rain water, well water – Double Junction Ag/AgCl reference

Waters:  Drinking water, tap water – Epoxy body for durability

Waters – Wastewater, seawater – Epoxy body and Double junction

Any electrode will work with any pH meter as long as the connections are the same.  Very precise pH measurements may require a pH half cell and reference half cell rather than a combination electrode(includes the reference in a single probe).

Robin Prymula