Potentiometric determination of chloride ions using glassy Ag–ISE in highly acidic aqueous mediа

Abstract

Chloride ions in the electrolyte significantly affect the corrosion of metals, cooking and heat exchange equipment of chemical processing of wood. Commercially produced Cl-ion-selective electrodes (Cl-ISE) with polycrystalline membranes made of pressed AgCl and Ag2S powders are chemically unstable in highly acidic media, insufficiently sensitive and selective for potentiometric determination of Cl––ions, in the presence of strong reducing agents and oxidants. The aim of the study was to determine the acid resistance and the possibility of ionometric application of Ag–ISE with monolithic membranes made of Ag–Ge (As)–S system glasses, as well as AgAsS2 and Ag3AsS3 single crystals as indicators of the end of potentiometric titration of Cl––ions in solutions of formic, acetic and nitric acids. Ion-conducting glassy materials for Ag–ISE sensor membranes were synthesized in evacuated quartz ampoules from especially pure elemental substances at 650 or 950 C and hardened in air. The acid resistance of sensor materials was determined by gravimetric method according to GOST 7343-41 in 10% aqueous solutions of НСОOH, CH3COOH and HNO3 at 17 ± 1 C for 250 h. Potentiometric measurements with an accuracy of ± 0.5 mV were carried out using an Ag–ISE electrochemical cell Ag–ISE | test solution¦1M NH4NO3 ¦ 1M KCl | AgCl, Ag. Potentiometric titration was performed using a microburet with a volume measurement accuracy of ± 0.01 ml. Homogeneous Ag+– sensor membranes made of Ag–Ge (As)–S system glasses or Ag3AsS3 single crystal are chemically stable in 10% aqueous solutions of formic, acetic and nitric acids (the dissolution rate at 17 C is less than 10 micrograms· cm–2 · h–1). Ag–ISE with acid-resistant glassy membranes Ag20Ge29S51 and AgAsS2 have a stable electrode potential and a gradient of the electrode function of 52–58 mV/ рAg at рAg = 1–5 and can be successfully used in solutions of formic, acetic and nitric acids with a concentration of up to 6 mol/ l for the determination of chloride ions by the method of potentiometric precipitation titration.