Chemical Metrology II: Estimation of Uncertainty in Measurement of pH in Water
DOI:
https://doi.org/10.5377/universitas.v2i1.1638Keywords:
Chemical metrology, uncertainty in pH measurement in water, expanded relative uncertainty in pH measurement, asymmetry potentialAbstract
The main objective of this study is to estimate the uncertainty in the determination of pH in a water sample, taking into account all the experimental parameters involved in the measurement process. To evaluate the uncertainty, the general procedure established in the GUM ISO 1995 guide was followed. The mathematical model was derived, which includes the effect of the asymmetry potential of the glass electrode used. All sources of uncertainty were identified through a cause-effect diagram. All uncertainty components were calculated and combined using the law of propagation of uncertainty to obtain the standard uncertainty value in the pH measurement of the water sample (upHx). A Pareto diagram was created, which shows that out of the 7 main sources of uncertainty, only the repeatability in the potential reading (Ex) of the sample and the uncertainty in the calculation of pH where the potential is null (pH0) influence the estimation of upHx, whose value was 0.05. The confidence interval found was 7.6 ± 0.11. The expanded uncertainty was calculated using the coverage factor t value at a 95% confidence level and 18 effective degrees of freedom.
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