Transient responses of glass electrodes in dilute solutions and freshwaters

Abstract

Glass electrodes respond slowly in dilute, nearly neutral solutions (l= 0.1–1 mmol dm^–3, pH 6–9) of either natural lake water or simple inorganic salts, taking ca. 10 min to equilibrate irrespective of whether the solution is flowing or static. Although buffer capacity and ionic strength influence the response, they are not critical factors. The transient effect is associated with low concentrations of cations. There was no great difference in response for the different cations tested, but the sluggishness appeared to increase in the order K⁺≈ Ca²⁺ < Na⁺≈ Mg²⁺ < NH₄⁺. The time dependence of the response is consistent with it being due to a diffusional exchange process. Glass electrodes are inappropriate pH sensors for the determination of the pH of dilute neutral solutions by flow injection analysis.