Determination of the Activity of Hydrogen Ions in Dilute Sulfuric Acids by Use of an Ionic Liquid Salt Bridge Sandwiched by Two Hydrogen Electrodes

Abstract

The activities of hydrogen ions in 20-200 μmol dm(-3) H(2)SO(4) solution were estimated by use of an ionic liquid salt bridge (ILSB), made of tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide (TBMOEPC(2)C(2)N), sandwiched by two hydrogen electrodes. The experimental pH values (pH = -log a(H), where a(H) is the activity of hydrogen ions) were in good agreement, within 0.01 pH unit, with those calculated using the Pitzer model. The difference between the experimental and theoretical pH values at 50 μmol dm(-3) H(2)SO(4) solution was much smaller than that obtained by use of a glass electrode in combination with a reference electrode with a concentrated KCl salt bridge. The source of the small deviation can be explained by the residual diffusion potential due to the dissolution of TBMOEPC(2)C(2)N in the H(2)SO(4) solution (W) and the resultant increase in the ionic strength of W. The use of a reference electrode equipped with an ILSB opens the way to accurately estimate the pH in dilute aqueous solutions, for which we have not had effective means.

Application of a pH Electrode Incorporating an Ionic Liquid Salt Bridge to the Measurement of Rainwater Samples

“…Sulfuric acid solutions at three different concentrations (20, 50, and 200 μmol dm -3 ) were prepared according to the procedure reported in a previous study. 23 The calculation of 2017 © The Japan Society for Analytical Chemistry † To whom correspondence should be addressed. E-mail: satoshi.nomura@horiba.com…”

“…Due to the dissolution of hydrogen phthalate ions in the IL phase, a potential shift of a few mV was found when IL-E was calibrated with a phthalate standard solution. 21 Therefore, the 0.05 mol kg -1 citrate buffer solution (pH = 3.776 at 298 K) was used instead of the phthalate standard solution in case of IL-E. 23,24 The pH was measured three times for 15 min at 298 ± 0.2 K for each sample. The average pH value obtained after 15 min, pH15, was defined as the experimental pH value for each solution.…”

“…[16][17][18][19][20][21][22][23][24] This electrode utilizes a reference electrode based on a new type of salt bridge with a completely different working principle. The new salt bridge relies on the partition of an ionic liquid (IL) instead of the diffusion of a concentrated KCl solution.…”

“…The experimental pH values were in good agreement within 0.03 pH units of the theoretical pH values. 23,24 In this work, the applicability of a pH electrode incorporating ILSB to the measurement of rainwater pH was assessed. A superior response, compared to the conventional electrode, was confirmed in terms of the deviation from theoretical pH values, the response time, and the elimination of any sample contamination.…”

Single-ion activity: Optical sensing vs. electrochemical sensing

“…All-solid-state reference electrodes have been described with conducting polymers as ion-to-electron transducers and PVC or acrylic membranes containing lipophilic electrolytes and also KCl, AgCl and metal silver [19][20][21]. Aqueous liquid junctions in Ag/AgCl electrodes were successfully replaced with suitable ionic liquids [22,23]. For optodes, E1 -30 21 -E2 ---450 E3 -30 21 45 O1 20 120 21 -O2 20 120 -20 O3 20 120 -60 use of non-transparent components like e.g.…”