So for a metal, the flow of electricity is due to free electrons that can move through the metal. But for liquids, there can be cations and anions that facilitate the transfer of charge. As far as I know there can be free electrons in liquids too that can also contribute to the flow of electricity through a liquid in addition to the movement of cations and anions that contribute to the movement of charge due to the presence of an electric field.
My question is, Is there a way to measure the conductivity of a liquid such that you only measure the contribution due to the free electrons in a liquid, excluding any contribution from the cations and anions? I know there are pH meters that can measure how many H+ cations there are, but I was wondering if there is an instrument or technique that can measure the contribution to the conductivity due to free electrons alone.
The only thing I can think of so far would be to freeze the liquid to stop the movement of any ions and to then measure its conductivity with a standard conductivity meter. But then I read somewhere that cations and anions could quantum tunnel and if this is the case they might still show up on any reading.