This technique is crazy! It allows to both:You actually see discrete peaks at different minute counts on the other end.
- separate gaseous mixtures
- identify gaseous compounds
It is based on how much the gas interacts with the column.
Detection is usually done burning the sample to ionize it when it comes out, and then you measure the current produced.
The procedure remind you a bit of gel electrophoresis, except that it is in gaseous phase.
Gas chromatography by Quick Biochemistry Basics (2019)
Source. How I invented the electron capture detector interview with James Lovelock by Web of Stories (2001)
Source. He mentions how scientists had to make their own tools during the 40s/60s. Then how gas chromatography was invented at the National Institute for Medical Research and gained a Nobel Prize. Lovelock came in improving the detection part of things.The name makes absolutely no sense in modern terms, as nor colors nor light are used directly in the measurements. It is purely historical.
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[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.
Ion selective electrode schematic
. Source. Sample calibration curve for an ion selective electrode
. Source. The curve is simple and log linear, so once you have that it is easy to fit new measurements to the curve.Ion selective electrodes Tech Tips by Vernier
. Source. 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.
Using an Ion Selective Electrode by University of Alberta
. Source. 
