Reconciling the pHe measurements of bioethanol: pHabs measurements of buffered 50-50 wt% water-ethanol mixtures

Ionic liquid salt bridge — Current stage and perspectives: A mini review

Potentiometric properties of the electrochemical cells equipped with ionic liquid salt bridge and its application to determine the solubility of the ionic liquid and the mean activity coefficients of the chloride salt of the ionic liquid-constituent cation in water

Thermodynamic quantities of single ions, such as the proton activity (i.e. pH values) or single ion Gibbs solvation energies (i.e. redox potential values), are widely used in chemistry and related sciences.[1] Thus, methods for the experimental determination of these values are of great interest. Our work focuses on the experimental determination of Gibbs transfer energies Δtrans G(i, S1 → S2) of the ion i, between the different solvents S1 and S2, as the central values for the solvent independent, unified acidity scale pHabs H2O and redox scale E abs H2O, and their two-dimensional combination, the Protoelectric Potential Map (PPM).[2] We established an 'ideal' ionic liquid salt bridge (ILSB) setup, using potential measurements between two electrochemical half cells (Fig. 1).[3] In this setup, the electroactive species is dissolved in different solvents, like water or acetonitrile, and the half-cells are connected by an ILSB. 'Ideal' regarding identical diffusion coefficients for both cation and anion of the ionic liquid to minimize liquid junction potentials at the phase boundaries.Up to now, our research focused on solvents with high permittivity, like water or acetonitrile, utilizing the redox systems Ag+/Ag and Cl2/Cl−.[4] Within this contribution, we present the E abs H2O-scale extended by measured transfer energies in low permittivity solvents, like dichloromethane or fluorobenzene, which are not compatible with the previous setup due to the low solubility of the redox systems used. For this application the redox systems Ag+/Ag and Ferrocenium/Ferrocene (Fc+/Fc) were used. In this way, we can include several values measured by cyclic voltammetry.[5] The E abs H2O-scale gives the experimental chemist the possibility of a more straightforward synthesis design and the theoretical chemist values to benchmark his calculations. REFERENCES P. Hünenberger, M. Reif, Single-ion solvation. Experimental and theoretical approaches to elusive thermodynamic quantities, Royal Society of Chemistry, Cambridge, 2011.V. Radtke, D. Himmel, K. Pütz, S. K. Goll, I. Krossing, Chem-Eur. J. 2014, 20, 4194.a) V. Radtke, A. Ermantraut, D. Himmel, T. Koslowski, I. Leito, I. Krossing, Chem. Int. Ed. 2018, 130, 2368; b) A. Ermantraut, V. Radtke, N. Gebel, D. Himmel, T. Koslowski, I. Leito, I. Krossing, Angew. Chem. Int. Ed. 2018, 130, 2372.a) V. Radtke, N. Gebel, D. Priester, A. Ermantraut, M. Bäuerle, D. Himmel, R. Stroh, T. Koslowski, I. Leito, I. Krossing, Eur. J. 2022, 28, e202200509.; b) V. Radtke, D. Priester, A. Heering, C. Müller, T. Koslowski, I. Leito, I. Krossing, Chem. Eur. J. 2023, 29, e202300609.I. Krossing, C. Armbruster, M. Sellin, M. Seiler, T. Würz, F. Oesten, M. Schmucker, T. Sterbak, J. Fischer, V. Radtke et al., e-preprint DOI: 10.21203/rs.3.rs-3921217/v1. Figure 1

A pH electrode incorporating a reference electrode different from that in conventional electrodes was applied to the measurement of rainwater pH. The reference electrode utilizes a recently proposed ionic liquid salt bridge instead of a conventional potassium chloride salt bridge. The response time of this electrode was remarkably improved in rain sample pH measurements compared to that of conventional pH electrodes. In addition, the measured pH values of rain samples seemed to be more accurate with this electrode.

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

Determination of single-ion activity coefficients of hydrogen and bromide ions in aqueous hydrobromic acid solutions based on an ionic liquid salt bridge

A new potentiometric method of determining the ionization constant of water based on the ionic liquid salt bridge consisting of N-ethyl-N-heptylpyrrolidinium bis(pentafluoroethanesulfonyl)amide

The use of the reference electrode equipped with an ionic liquid salt bridge in electrochemistry of ionic liquids: A convenient way to align the formal potentials of redox reactions in ionic liquids based on the standard hydrogen electrode scale

The liquid junction potential (LJP) across the two phases is very important for the basic science and real application of electrochemistry. In the case of the reference electrode the KCl salt-bridges are widely used, because the diffusion potential can be neglected in some cases by the almost same mobility of potassium ion and chloride ion in aqueous solution. However, if the difference of the concentration of solute between the two phases is great the LJP becomes several ten mV. And in the KCl salt-bridge KCl solution flow from reference electrode to the sample solution is essentially inevitable. To overcome these shortcomings of KCl salt bridge Kakiuchi et al. introduced the ionic liquid salt bridge (ILSB) concept and found that LJP for ILSB is always constant and independent on the concentration of electrolyte in aqueous phase. The LJP for ILSB is distribution of cation an anion of IL to aqueous solution.[1] In the present study we have measured the electric conductivity of lithium bis(pentafluoroehtanesulfonyl)amide (LiC2C2N) and bis(pentafluoroethanesulfonyl)amide acid(HC2C2N) in aqueous solution. C2C2N anion is the ionic liquid component of ILSB and the cation is tributyl(2-methoxyethyl)phosphonium (TBMOEP). Form the conductivity measurements we have found that the molar conductivity at infinite dilution of C2C2N anion is 28.1 ± 0.7 S cm2 mol-1 and mobility is 2.91 × 10-4 cm2 V-1 s-1. Sakaida et al. reported the solubility of TBMOEP cation in aqueous solution is 2.64 x 10-4 cm2 V-1 s-1.[2] From these results we can estimate the diffusion potential across TBMOEPC2C2N | HCl solution using the Henderson equation. Even in the case of 0.5 mmol dm-3 the magnitude of the diffusion potential is 60 microvolt and the we can conclude that the diffusion potential is negligible in the TBMOEPC2C2N ILSB. We are now investigating the coupled Nernst-Plank and Poisson-Boltzmann equation to see the detail of the potential and the concentration profile. From the conductivity measurements we also found that HC2C2N is strong acid and C2C2N anion in aqueous phase is completely dissociated.

A reference electrode equipped with ionic liquid salt bridge consisting of tributyl(2-methoxyethyl)phosphonium bis(pentafluoroethanesulfonyl)amide has been employed for potentiometric precipitation titration of chloride with silver ions in water at 25 °C. A model for the titration curve was regressed to experimental curves, taking into account the change in the activity coefficients of relevant ionic species in the course of the titration, to obtain the least square estimates of two adjustable parameters in the model, the solubility product (K sp ) and the analyte concentration. The least-square estimate of K sp , (1.840 + 0.060) × 10 −10 , i.e., pK sp = 9.736 + 0.014, is in good agreement with literature data, but with higher precision.

A new type of salt bridge composed of a hydrophobic room-temperature ionic liquid, recently proposed (T. Kakiuchi and T. Yoshimatsu, Bull. Chem. Soc. Jpn., 2006, 79, 1017), has been shown to be satisfactorily usable in dilute aqueous solutions of submillimolar range. A stable phase-boundary potential has been demonstrated between an ionic liquid, 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(8)mim+][C(1)C(1)N-), and an aqueous KCl solution of submillimolar level, which is lower than the solubility of [C(8)mim+][C(1)C(1)N-] in water, 1.6 mmol dm(-3) at 25 degrees C. The phase-boundary potential between [C(8)mim+][C(1)C(1)N-] and water is maintained constant over more than four orders of magnitude change in the concentration of an aqueous electrolyte solution. The ionic-liquid salt bridge is a superior alternative to salt bridges based on equitransferent electrolytes in practical applications, particularly, the potentiometry of samples of low ionic strengths, such as potentiometric pH measurements of rainwater.

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.

A new type of ionic liquid salt bridge (ILSB) based on a mixture of pentyltripropylammonium bis(pentafluoroethanesulfonyl)amide, [N(3335)(+)][C(2)C(2)N(-)], and heptadecafluorodecyltrioctylphosphonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, [TOPH(+)][TFPB(-)], shows a stable phase-boundary potential (Δ(IL)(W)φ) between the ILSB and an aqueous solution of MCl (M = H(+), Li(+), Na(+), and K(+)) over the concentration range from 0.05 mM to 0.5 M with an averaged excursion in 1 h of ±0.3 mV. The reproducibility of Δ(IL)(W)φ is ±0.6 mV on average (95% confidence interval) in KCl solutions in this concentration range. The mixing of the two different types of salts not only increases the stability of the phase-boundary potential but provides us with more freedom in selecting potential-determining salts to design and customize ILSBs for different purposes.

Single ion activity coefficients of chloride ions in aqueous sodium chloride and magnesium chloride estimated potentiometrically based on ionic liquid salt bridge at 298 K

Ionic liquid salt bridge based on N-alkyl-N-methylpyrrolidinium bis(pentafluoroethanesulfonyl)amide for low ionic strength aqueous solutions