Uncertainties in Determination of pH |
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Authors: | Günther Meinrath Petra Spitzer |
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Affiliation: | (1) RER Consultants, Schieβstattweg 3a, D-94032 Passau, Germany, DE;(2) Institut für Hydrogeologie, TU Bergakademie Freiberg, G.-Zeuner-Str. 12, D-09596 Freiberg, Germany, DE;(3) Institut für Anorganische Chemie, TU Bergakademie Freiberg, Leipziger Str. 29, D-09596 Freiberg, Germany, DE;(4) Physikalisch-Technische Bundesanstalt, Bereich 3.21 Metrologie in der Chemie, Bundesallee 100, D-5312 Braunschweig, Germany, DE |
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Abstract: | A statistical analysis of multi-point calibration procedure for practical measurement of pH under laboratory conditions is given. The procedure is shown to provide the necessary elements for simple assignment of an uncertainty to a pH measurement – an essential element of quality control. Performance of ordinary least squares regression for prediction of confidence limits is compared to orthogonal regression, inverse regression and Monte Carlo simulations. In case of pH measurement by multi-point calibration procedure, methods considering uncertainties in both axes are found to be statistically more satisfactory than ordinary least squares regression. By analysis of 50 pH calibration data, randomly selected from 250 5-point glass electrode calibrations, it is found that the practical differences, however, are of minor importance. The significance of uncertainty in pH is demonstrated for an example from metal ion speciation in aqueous solution. Received September 20, 1999. Revision April 19, 2000. |
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Keywords: | : Chemical thermodynamics environmental prognosis pH electrode calibration statistical analysis uranium solubility. |
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