Potentiometric determination of pH values of dilute sulfuric acid solutions with glass combination electrode equipped with ionic liquid salt bridge

The pH of dilute aqueous sulfuric acid solutions in the concentration range between 20 and 200 μmol dm−3 has been accurately determined by use of glass combination electrodes, in which the reference electrode is equipped with an ionic liquid salt bridge (ILSB) made of gelled tributyl (2-methoxyethyl) phosphonium bis(pentafluoroethanesulfonyl)amide (TBMOEPC2C2N). Experimental pH values determined by calibration of the electrodes with two pH standard buffer solutions are in agreement within 0.03 pH unit with theoretical pH values at all concentrations of H2SO4 studied. The difference at 50 μmol dm−3 H2SO4 solution is smaller by 0.03 pH unit than that obtained previously by Metcalf ( Analyst 112 (1987) 1573) using conventional glass combination electrodes based on KCl salt bridge (KClSB). The ILSB enables us to accurately determine pH values of low ionic strength aqueous solutions with the same protocol as that used to date in pH measurements based on glass electrode paired with KClSB-equipped reference electrode. The response times of the ILSB-type glass combination electrodes in pH measurements of low ionic strength solutions are shorter than those of KClSB-type glass combination electrodes because the change of ionic strength in a sample during the pH measurement with ILSB-type is small by virtue of the low solubility of the ionic liquid used as a salt bridge into water.