ISE’s are not perfect. They do suffer from interferences of other ions to a greater or lesser degree.

The best advice is to consult the ISE table. If there is an ion present in the samples that is listed as an interferent then you will need to think about a few points:

• If the ions you are measuring are greater in concentration than the interferent you can usually ignore it.
• In many instances interfering ions can be eliminated using chemicals.
• You can use incremental techniques, e.g. Known Addition.