Influence of buffer quality on pH measurement uncertainty: prediction and experimental evaluation |
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Authors: | Irina Ekeltchik Elena Kardash-Strochkova Orna Dreazen I Kuselman |
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Institution: | (1) Chemistry Department,Tomsk State University, Lenin av. 36, Tomsk 634050, Russia, RU;(2) National Physical Laboratory of Israel (INPL), Givat Ram, Jerusalem 91904, Israel e-mail: ilya_kus@netvision.net.il Tel.: +972–2-6536 534 Fax: +972–2-6520 797, IL;(3) Israel Laboratory Accreditation Authority, 2 Ha-Bonim Street, Ramat Gan 52322, Israel, IL |
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Abstract: | Dependence of the uncertainty of a pH measurement result on the quality of buffers (i.e. the uncertainty of their certified
pH values) at different levels of instrumental uncertainty (pH-meter, etc.) was simulated using the Monte Carlo method and
regression analysis. The contribution of the instrumental standard uncertainty (in the studied range from 0.1 to 1 mV) to
the uncertainty of the pH measurement result is negligible, if the standard uncertainties of the pH buffers exceed 0.04 pH
(e. g. for in-house buffers). It is shown how the choice of pH-meter and buffers should be correlated in order to meet the
required uncertainty of a pH measurement result in a sample under analysis. The results of the simulation were compared with
experimental data obtained from calibrations of a pH/ion-meter with a hydrogen working electrode (Radiometer PHM-240) and
with a glass electrode (Metrohm 744). Buffers of different quality (National Institute for Standards and Technology standard
reference materials, certified Radiometer buffers and Merck CertiPUR buffers) were used for the calibrations. The uncertainties
of the experimental results are close to the predicted ones obtained by the simulation.
Received: 16 June 2002 Accepted: 19 July 2002
Presented at the 14th International Conference of the Israel Society for Quality, 18–21 November 2002, Jerusalem, Israel
Correspondence to I. Kuselman |
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Keywords: | Measurement uncertainty pH Monte Carlo method Calibration Buffers |
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