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Objective 1: Universally applicable measurement procedure for pHabs, including uncertainty budgets

The project will create a measurement procedure for the proposed unified pH scale (on the basis of differential potentiometry with glass electrodes specially designed for working in non-aqueous solutions). The measured pH
abs values will be characterised by rigorous uncertainty budgets taking into account all main uncertainty contributions – repeatability/intermediate precision of comparison, drift of the system, possible incomplete elimination of LJP components. As a result of this project a detailed measurement uncertainty model will be developed and the following combined standard uncertainties are expected: 0.15 pHabs in "good" (mixed aqueous, alcohols, etc.) and 0.25 pHabs in "difficult" (colloids, aprotic, etc.) systems (these are "absolute uncertainties" in terms of the pHabs scale, comparison of pHabs values will be possible with much lower uncertainty of the order of 0.05 pHabs).

Objective 2: Reliable method for the evaluation of the LJP between aqueous and non-aqueous solutions

The issue of LJP will be addressed without extrathermodynamic assumptions by: (1) utilising an “ideal” ionic liquid salt bridge composition that eliminates contribution from different mobilities of ions (part A) and contribution from different solvation free energies of ions (part B) and (2) measuring the contribution resulting from different physicochemical properties of the solvents forming the junction (part C). A suitable “ideal”
ionic liquid – with identical mobilities and solvation energies of anion and cation – will be used as salt bridge electrolyte.

Objective 3: Coherent and validated suite of calibration standards for routine measurement of pHabs

Using the solvent-independent standard state makes the pH
abs measured in a medium comparable to pHabs measured in any other medium. The obtained pHabs values will be rigorously linked with the aqueous pH scale, yielding pHabsH2O-values by applying a constant offset in such a way that in aqueous solutions the pHabsH2O-value is equal to the conventional aqueous pH-value. The project will provide procedures for creating a coherent system of calibration standards for standardising routine measurement systems in terms of pHabsH2O values. pHabsH2O-values in any other solvent/medium can be directly compared to the well-known aqueous pH scale. This will also eliminate the need to experimentally create the (unrealistic in practical terms) 1 bar proton gas standard state, as practical reference can be made to an aqueous standard state with pH 7.0.
Moreover, feasibility studies into developing a novel solid state redox pH sensor enabling to measure pH
abs will be performed as well as guidelines dedicated to implementing specific approaches for practical usage of the unified pH values by practicing chromatographers will be delivered.
Once the measurement standards (reference materials), accurately characterised in terms of
pHabsH2O, are available, they can be used by routine laboratories for measuring pHabsH2O and – very importantly – using their routine pH measurement equipment (i.e., there will be no need for routine laboratories to install sophisticated differential potentiometry setups). As specific example, such standard will be created for ethanol in relation to the needs for international specifications for bioethanol quality e.g. EN 15490.

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