Double junction reference electrodes are typically used for ISE analysis where the leached electrolyte must not interfere with the ISE being used.

They are also particularly useful for pH analysis of products that must not have KCl or a strong electrolyte contaminating the sample. The inner junction is filled with Ag/AgCl (refillable). The outer can be filled with the electrolyte of your choosing (see filling solutions) to suit the application.

This electrode  comes filled with Potasium Nitrate solution as standard