DETERMINATION OF pH VALUES FOR REFERENCE POTASSIUM HYDROGEN PHTHALATE BUFFER IN WATER-ETHANOL MIXTURE (MASS FRACTION 50 %)

D. Stoica, P. Spitzer, F.B. Gonzaga, I. Maksimov, P. Fisicaro, B. Adel, I.C. Fraga, T. Asakai, P.P Borges, A Hioki

Abstract

Currently, the metrological traceability of pH measurements for bioethanol is not ensured due to the lack of ethanol based reference buffer solutions. This situation leads users to calibrate their pH-electrode by means of aqueous buffer solutions, creating serious problems of reliability of measurement results. The potassium hydrogen phthalate (KHPh) solution with molality 0.05 mol·kg^-1 was studied as a possible primary buffer in water-ethanol mixture (mass fraction 50 %). The study was carried out in the temperature range from 15 °C to 35 °C.<BR />For this purpose, the potentiometric method based on the Harned cell (cell without liquid junction) typically employed for the characterisation of primary dilute aqueous buffer solutions has been used. In order to assess the comparability of primary pH values on KHPh buffer, the results obtained by four NMIs (National Metrology Institutes) will be presented.

Keywords

standard potential, water-ethanol mixture, primary pH measurements

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IMEKO-WC-2012-TC24-O4.pdf

DOI

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IMEKO TC

TC24 - Chemical Measurements

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