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Treatment of bimodality in proficiency test of pH in bioethanol matrix

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Abstract

The pH value in bioethanol is a quality control parameter related to its acidity and to the corrosiveness of vehicle engines when it is used as fuel. In order to verify the comparability and reliability of the measurement of pH in bioethanol matrix among some experienced chemical laboratories, reference material of bioethanol developed by Inmetro—the Brazilian National Metrology Institute—was used in a proficiency testing (PT) scheme. There was a difference of more than one unit in the value of the pH measured due to the type of internal filling electrolytic solutions (potassium chloride, KCl, or lithium chloride, LiCl) from the commercial pH combination electrodes used by the participant laboratories. Therefore, bimodal distribution has occurred from the data of this PT scheme. This work aimed to present the possibilities that a PT scheme provider can use to overcome the bimodality problem. Data from the PT of pH in bioethanol were treated by two different statistical approaches: kernel density model and the mixture of distributions. Application of these statistical treatments improved the initial diagnoses of PT provider, by solving bimodality problem and contributing for a better performance evaluation in measuring pH of bioethanol.

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Authors and Affiliations

  1. Chemical Metrology Division (Dquim), National Institute of Metrology, Quality and Technology (Inmetro), Av. Nossa Senhora das Graças, 50, Xerém, Rio de Janeiro, 25250-020, Brazil

    Gabriel F. Sarmanho, Paulo P. Borges & Isabel C. S. Fraga

  2. Corporate Management Division (Dgcor), National Institute of Metrology, Quality and Technology (Inmetro), R. Santa Alexandrina, 416, Rio Comprido, Rio de Janeiro, 20261-232, Brazil

    Luiz H. da C. Leal

Authors
  1. Gabriel F. Sarmanho
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  2. Paulo P. Borges
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  3. Isabel C. S. Fraga
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  4. Luiz H. da C. Leal
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Correspondence to Gabriel F. Sarmanho.

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Sarmanho, G.F., Borges, P.P., Fraga, I.C.S. et al. Treatment of bimodality in proficiency test of pH in bioethanol matrix. Accred Qual Assur 20, 179–187 (2015). https://doi.org/10.1007/s00769-015-1133-4

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