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pH is a widely used control parameter for several industrial processes. Thus, its correct determination and uncertainty estimation are extremely important. The Guide to the Expression of Uncertainty in Measurement (ISO-GUM) has been extensively used for pH uncertainty estimation. This work uses Monte Carlo simulation to estimate pH uncertainty in a primary pH system for the measurements of a regional comparison (SIM 8.11P-1) in which INMETRO has participated. The results are compared with the ISO-GUM analytical estimation approach and good agreement was found.

The importance of Brazilian bioethanol as biofuel has been increasing significantly. Its origin from renewable sugar cane is able to reduce carbon in the atmosphere and is one of the factors that contribute for reducing global warming. Because of the difficulty in measuring pH in nonaqueous solutions, Inmetro, the Brazilian Metrology Institute, has focused its attention on the needs for accurate and reliable pH measurements, as part of its work in developing and producing certified reference material (CRM) of bioethanol. This paper aims to present the studies of pH measurement in CRM of bioethanol from sugar cane (approximately 99.6 % ethanol content) using two commercial pH electrodes with different internal filling electrolytic solutions. One electrode, containing potassium chloride (KCl), was specified in the American standard, ASTM D6423, and the other one, containing lithium chloride (LiCl), was specified in the Brazilian standard, ABNT NBR 10891, and European standard EN 15490. These studies have shown that there was a significant difference among the pH values (more than 1.0 pH unit) measured by the different electrodes related to its internal filling solution. The results have shown that a harmonization of the standardization on the pH measurement is needed in order to make possible its use and application as analytical parameter.

The key comparison CCQM-K96 was organized jointly by the inorganic and electrochemistry working groups of CCQM to test the abilities of the metrology institutes to measure the amount content of dichromate. Slovak Institute of Metrology with help of KRISS acted as the coordinating laboratories. Eight NMIs took part in the comparison. All participants used high accuracy constant current coulometry. Good agreement of the results was observed.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

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