What are the types of ISE electrodes?

Document ID

Document ID TE2810

Version

Version 4.0

Status

Status Published

Published Date

Published Date 07/19/2018
Question
What are the types of ISE electrodes?
Summary
ISE electrode types
Answer
There are four types of ISEs with different sensor designs and operation:

1. Glass membrane ISEs - This type of ISE is equivalent to a pH probe. Whereas a pH probe’s glass is selective to hydrogen ions, glass membranes ISEs have special “doped” glass that is sensitive to selected ions in solution. Hach’s IntelliCAL™ ISENa381 Sodium electrode is an example of this type of ISE.

2. Crystalline membrane ISEs - In this type of ISE, the electrode potential is measured across a solid, polished crystalline membrane. The crystal is prepared from a single compound or a homogenous mixture of compounds. These types of electrodes are often referred to as “solid‐state electrodes” This is due to their long life and relatively minor maintenance requirements. Hach’s IntelliCAL™ ISEF121 Fluoride electrode is an example of this type of ISE.

3. Polymer membrane ISEs - This type of ISE contains a solid, polymeric membrane, containing a selective ion material. The electrode potential of solutions is measured by their effect on this ion exchange material. These membranes are often replaceable, depending on the design of the specific electrode. This is because these types of membranes typically have a short life and can easily be damaged by harsh sample types or if not maintained properly. Hach’s IntelliCAL™ ISENO3181 Nitrate electrode is an example of this type of ISE. However, the Hach IntelliCAL polymeric ISEs differ from traditional electrodes of this type in that they can be considered “solid state”. The Hach Ammonium and Nitrate probes utilize proprietary polymer membrane and reference designs that allow for dry storage and low maintenance. These probes contain sensing and reference components designed to last up to two years within typical customer use and sample types.

4. Gas sensing ISEs - This type of ISE uses a gas sensing membrane element. These electrodes have a gas permeable membrane and an internal filling solution. The gaseous form of the selected ion permeates through the membrane and changes the pH of the filling solution. A standard pH glass bulb inside the permeable membrane then measures the pH. The change in pH is proportional to the concentration of the ion. Hach’s IntelliCAL™ ISENH3181 Ammonia electrode is an example of this type of ISE.

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