Reference electrodes for use in the potentiometric determination of chloride. Part III. Chloranil electrodes

Abstract

Reference electrodes consisting of platinum electrodes immersed in solutions of constant pH saturated with tetrachlorobenzoquinone and tetrachlorohydroquinone have been tested for use in the potentiometric determination of chloride. The composition of the solution inside the reference electrode is matched with the main components of the treated sample solution (i.e., after addition of reagents to control pH and ionic strength but excluding chloride itself). In this way the effect of the liquid junction potential is minimised. The electrodes have a sealed construction, need no maintenance and can be used immediately on assembly.

Electrodes containing a 0.01 mol l^–1 nitric acid filling solution [for use with mercury(I) chloride sensing electrodes] had no significant rate of drift in e.m.f. over the 11 weeks of the test and in this respect were superior to any other reference electrode tested for chloride determination. The precision of the measurements was also better than had been obtained before. This type of electrode is better in every way than other experimental electrodes tested previously that worked on the same principle but used a less stable organic component (benzoquinhydrone). Compared with the mercury-mercury(I) sulphate electrode, the new electrode has the disadvantage of a larger dependence on pH but is otherwise equal or superior.

Electrodes containing a pH 4.5 acetic acid-ammonïum acetate buffer solution (for use with silver chloride electrodes) were much better than earlier electrodes based on benzoquinhydrone, but differed only marginally in performance from the usual mercury-mercury(I) sulphate reference electrode.