Dear all!
I think the main functions of pores are to avoid the contact of the two different liquids and just allow the passage of ions, so I think the pore size should be small enough to block the liquid, although the solvated ions must pass through it.
For glass frits, in the following link, you can find a table showing the different nominal ranges of pore sizes in micrometers
https://www.chemie.de/lexikon/Glasfritte.html
Best
Marco
Dear Marco,
The junction between a reference electrolyte and a sample solution should prevent mixing the two solutions, not the contact of them (and prevent contamination of the sample by e.g. chloride ions). Generally, a permanent outflow of the reference electrolyte solution is recommended, normally, at the level of several microliter per hour, which provides a low resistance and low junction potential. As for the glass frit pore size, the range from 2 (commonly designated P5 or G5) to 40 (P3 or G3) micrometres is considered to be suitable.
Best,
Rouvim Kadis
To be more specific, glass frits with considerably smaller pore sizes (down to the nanometer range) are commonly used in commercial reference electrodes designed for routine measurements, while frits with larger pore sizes are used in apparatus designed for accurate emf measurements in a potentiometric cell. The former application of porous frit junctions has been analyzed by M.P.S. Mousavi et al. Anal. Chem. 2016, 88, 17, 8706-8713Article Avoiding Errors in Electrochemical Measurements: Effect of F...
As examples of the latter application, the evaluation of the liquid junction potential in a cell with frits of G3 porosity (E.E. Johnsen et al. Z. Phys. Chem. 1990, 168, 101-114) and the standardization of pH reference materials in a differential cell with the frit of G4 porosity (F.G.K. Baucke. J. Electroanal. Chem. 1994, 368, 67-75) can be mentioned.Best regards,
Rouvim Kadis
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