A polyvinylchloride-membrane based anion selective electrode for continuous registration of ΔpH (interior alkaline) with salicylate as the indicator probe

Abstract

An anion sensitive electrode has been constructed with the use of the lipid soluble cation benzyl-dimethyl-hexadecylammonium analogous to the procedure described for tetraphenylphosphonium-sensitive electrodes [Shino, T., Kamo, N., Kurihara, K. and Kobatake Y. (1978) Arch. Biochem. Biophys. 187, 414–422]. The anion electrode responds to salicylate concentrations above 400 μM with a Nernstian sensitivity. Less lipid soluble anions like chloride and phosphate do not interfere. Below 400 μM salicylate the response of the electrode decreases gradually so that the sensitivity of the electrode is less than 10 mV per decade change at concentrations of the anion of 50 μM. A computer program has been developed to fit the electrode response curve with a polynomal function of the fourth power. Additional software allows calculation of changes in the concentration of the salicylate anion, also under conditions where the sensitivity of the electrode for the anion is not constant. In this way the electrode can be used to measure changes in salicylate concentration that occur in a suspension of bacteria when, upon energization, a pH gradient is generated. 31P nuclear magnetic resonance measurements demonstrated that the pH gradient measured with the salicylate-sensitive electrode in the phototrophic bacterium Rhodopseudomonas sphaeroides is quantitatively correct. The response time of the electrode decreases from 1 min at 20 μM salicylate to 10 s at concentrations ⩾ 200 μM.