Journal
SENSORS
Volume 21, Issue 11, Pages -Publisher
MDPI
DOI: 10.3390/s21113935
Keywords
pH(abs); ionic liquid salt bridge; commercial glass electrodes; water-alcohol mixture; non-aqueous pH
Funding
- Estonian Research council grant [PRG690]
- EU through the European Regional Development Fund [2014-2020.4.01.01.15-0011, TK141]
- EMPIR program [17FUN09]
- European Union's Horizon 2020 research and innovation program [17FUN09]
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The study presents the authors' experience in measuring pH(abs)(H2O) values in mixtures of methanol, ethanol, and acetonitrile, with water, without the presence of buffers or other additives, using differential potentiometry and the 'pH(abs)-ladder' method. The introduction of the unified pH concept offers a way to compare pH values between solvents, addressing the issue of conventional pH values' incomparability. However, practical challenges remain in this research field, including the selection of commercial electrodes and ensuring comparability between laboratories.
Measurement of pH in aqueous-organic mixtures with different compositions is of high importance in science and technology, but it is, at the same time, challenging both from a conceptual and practical standpoint. A big part of the difficulty comes from the fundamental incomparability of conventional pH values between solvents ((s)pH, solvent-specific scales). The recent introduction of the unified pH (pH(abs)) concept opens up the possibility of measuring pH, expressed as pH(abs)(H2O), in a way that is comparable between solvent, and, thereby, removing the conceptual problem. However, practical issues remain. This work presents the experience of the authors with measuring pH(abs)(H2O) values in mixtures of methanol, ethanol, and acetonitrile, with water, but without the presence of buffers or other additives. The aim was to assigned pH(abs)(H2O) values to solvent-water mixtures using differential potentiometry and the 'pH(abs)-ladder' method. Measurements were made of the potential difference between glass electrodes immersed in different solutions, separated by an ionic liquid salt bridge. Data were acquired for a series of solutions of varying solvent content. This work includes experiences related to: a selection of commercial electrodes, purity of starting material, and comparability between laboratories. Ranges of pH(abs)(H2O) values for selected compositions of solvent-water mixtures are presented.
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