Treatment of bimodality in proficiency test of pH in bioethanol matrix

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 (RM) 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 aims 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.Comment: 20 pages, 6 figures, Accepted for publication in Accreditation and Quality Assurance (ACQUAL

Seleção intrapopulacional em milho.

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Ensaio regional e campos de observação de milho.

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The carbon isotopic (13C/12C) signature of sugarcane bioethanol: certifying the major source of renewable fuel from Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Ethanol has been increasingly used worldwide as a major renewable fuel. Since it can be produced from several matrixes such as sugarcane, corn, wheat, grape and beet, it has become important for certification purposes to verify the geographical origin and the different raw materials used for ethanol production. In this work, isotope ratio mass spectrometry, coupled to gas chromatography, was used to measure the carbon isotopic signature (delta C-13(V-PDB)) of Brazilian sugar cane bioethanol. Statistical data analysis was also applied to establish a probabilistic profile for the isotopic signature of major renewable Brazilian fuel. Other bioethanol samples produced from different raw materials in the USA and France were also analysed, for comparison.Ethanol has been increasingly used worldwide as a major renewable fuel. Since it can be produced from several matrixes such as sugarcane, corn, wheat, grape and beet, it has become important for certification purposes to verify the geographical origin and71147804785FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPERJ - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DO RIO DE JANEIROCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)sem informaçãosem informaçãosem informaçãosem informaçãoWe thank the State of São Paulo Research Foundation (FAPESP), State of Rio de Janeiro Research Foundation (FAPERJ), the Brazilian National Council for Scientific and Technological Development (CNPq) and the Financing Agency of Studies and Projects (FINEP