Reference electrode with internal diffusion barrier

In a double junction electrode comprising

• (a) a first housing containing an electrochemical half-cell being electrically connectable to an external measuring means and consisting essentially of a half-cell electrode and a half-cell electrolyte,
• (b) a second housing containing a junction electrolyte,
• (c) a half-cell junction allowing ionic conduction between said half-cell electrolyte and said junction electrolyte, and
• (d) a reference junction allowing ionic conduction between said junction electrolyte and an external sample to be measured, the improvement which comprises said half-cell junction comprising a microporous barrier material having a structure of sufficiently fine pore size such that exchange between half-cell and junction electrolytes is limited by diffusion, rather than by flow, characterized in that, when said half-cell junction is saturated with 4 M KCl, the mathematical quotient of the liquid flow rate through said half-cell junction at 1 cm Hg pressure divided by the ionic electrical conductance of said half-cell junction is less than about 0.12 ml.hr.sup.-1.mho.sup.-1.