Transient potential shifts with pH glass electrodes due to divalent cations

Abstract

The introduction of low concentrations of Cu²⁺, Ni²⁺, Co²⁺, Mn²⁺, Zn²⁺, Cd²⁺ and Hg²⁺ salts into unbuffered aqueous solutions gave rise to transient potential shifts with glass pH electrodes. These shifts mimic transitory pH decreases in solution. Removal of the added cation gave rise to a transient potential shift in the opposite direction. The relative order of magnitude due to the added cations was studied. The quasi-pH shifts were shown to be particularly serious in flow cells where the vigour of mixing was less and could easily lead to the impression that an actual pH transient had occured. The effects were shown to be due to a surface action at the glass membrane. A possible mechanism is suggested.