Uncertainities of pH-values from multipoint calibration

摘要

Multipoint calibration of electrodes for determination of pH-values is described using ordinary least square techniques. Calculation of the electrode parameters as measured slope k', electromotive efficency ss and zeropotentical-point pH_(0) are given for centre/slope- and intercept/slope-definition of the calibration line. The estimated standard deviations of these electrode parameters sdv (k'), sdv (ss), sdv (pH_(0)) are given. The uncertainity of measurement u_(r) and of the measured pH-value U(pH) is calculated by means of error propagation. Symbols and abbreviations text formulas standard pH values pH(S) x_(c) measured pH values pH(M) y_(c) EMF of standard buffer solution E(S) y_(c) EMF of unknown solution E(X) y_(a) measured pH value of unknown solution pH(m) y_(a) calculated pH of unknown solution pH(X) x_(a) number of buffer solutions N n_(c) Nernst slope k measured slope k' electromotive efficiency ss uncertainity of measurment u_(r) uncertainity of labeled pH value U(pH)