bridge solution

in pH measurement
Solution of high concentration of inert salt, preferably comprising cations and anions of equal mobility, optionally interposed between the reference electrode filling and both the test and standard solution, when the test solution and filling solution are chemically incompatible. This procedure introduces into the operational cell a second liquid junction formed usually in a similar way to the first. (This definition refers to a bridge solution of a double junction reference electrode.)
PAC, 1985, 57, 531. 'Definition of pH scales, standard reference values, measurement of pH and related terminology (Recommendations 1984)' on page 541 (