The determination of fluoride is a classic one. It was the only experiment we did on crystalline membrane ISEs. (We also used TISAB, a helpful solution for the experiment, to make more accurate measurements). I didn't even mention crystalline membrane ISEs...

There have been many discussions around fluoride use in water hahahhaha. Here in Europe it's not present. But as far as I know, fluoride is still placed on other common products, like table salt.


Nice article

{title2}
{wiki}

An <ion selective electrode> is tool used in  <analytical chemistry> used to determine the concentration of a given <ion> in a solution.

The method can determine the concentration of one ion even if there are multiple different types of <ion> in the solution, although in some cases this can alter the results. This is done with the help of a selective membrane that only allows certain ions through.

One cool example application mentioned on <LibreTexts>https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Physical_Methods_in_Chemistry_and_Nano_Science_(Barron)/01%3A_Elemental_Analysis/1.07%3A_Ion_Selective_Electrode_Analysis{ref} is the measurement of <fluorine> concentration in water. They explain that <fluorine> is added to the drinking water supply in some countries to help protect people's teeth, and so you want to be able to measure as part of quality control to make sure it is being added in correct the quantities.

The method requires calibrating with calibrating solutions which takes one hour, but once you are calibrated you just stick the sensor into the <analyte> and get readings in a minute without any expendables. The membrane seems to be a bit fragile which requires care, but overall it looks like a convenient method.

\Image[https://upload.wikimedia.org/wikipedia/commons/9/95/General_ISE_Set-Up.png]
{title=<Ion selective electrode> schematic}
{height=600}

\Image[https://web.archive.org/web/20220605032719im_/https://files.mtstatic.com/site_4334/142875/0?Expires=1654403194&Signature=aAPjJy6lmj0OVoTs6TFibKDDW1XlYFMdZp9qCdNChcca6NCOaHHQqFu1oH9gzt6Dwe2YZMW1WdaPkvN8kAoW29qoXQ-ExXs9XeIA0AhtuQSO3GvNXaiVISse2zEWtHB2wYz5KRggWJ6qHk34z8Jti8w5V0Qwqg6hK6RHt5AmGkw_&Key-Pair-Id=APKAJ5Y6AV4GI7A555NA]
{title=Sample calibration curve for an <ion selective electrode>}
{description=The curve is simple and log linear, so once you have that it is easy to fit new measurements to the curve.}
{height=600}
{source=https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Physical_Methods_in_Chemistry_and_Nano_Science_(Barron)/01%3A_Elemental_Analysis/1.07%3A_Ion_Selective_Electrode_Analysis}

\Video[https://www.youtube.com/watch?v=bGO_GvpVwVU]
{title=General Principles of Ion Selective Electrodes by Jacob Stewart}

\Video[https://www.youtube.com/watch?v=5NREQwnaGcE]
{title=<Ion selective electrodes> Tech Tips by Vernier}
{description=
The plump <Asian American> lady with a <PhD> explains how to use the thing.

It seems like a proprietary training video given with the product that this Peruvian university decided to upload to <YouTube>. Heroes.
}

\Video[https://www.youtube.com/watch?v=NHByG4g5-RE]
{title=Using an Ion Selective Electrode by <University of Alberta>}

Bibliography:
* https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Physical_Methods_in_Chemistry_and_Nano_Science_(Barron)/01%3A_Elemental_Analysis/1.07%3A_Ion_Selective_Electrode_Analysis


 Discussion on "Ion selective electrode" by Ciro Santilli (@cirosantilli, 37)