Under the auspices of the Organic Analysis Working Group (OAWG) of the Comité Consultatif pour la Quantité de Matière (CCQM) a key comparison, CCQM K55.b, was coordinated by the Bureau International des Poids et Mesures (BIPM) in 2010/2011. Nineteen national measurement institutes and the BIPM participated. Participants were required to assign the mass fraction of aldrin present as the main component in the comparison sample for CCQM-K55.b which consisted of technical grade aldrin obtained from the National Measurement Institute Australia that had been subject to serial recrystallization and drying prior to sub-division into the units supplied for the comparison.Aldrin was selected to be representative of the performance of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molar mass range 300 Da to 500 Da] and low polarity (pKOW < −2) for which related structure impurities can be quantified by capillary gas phase chromatography (GC).The key comparison reference value (KCRV) for the aldrin content of the material was 950.8 mg/g with a combined standard uncertainty of 0.85 mg/g. The KCRV was assigned by combination of KCRVs assigned by consensus from participant results for each orthogonal impurity class. The relative expanded uncertainties reported by laboratories having results consistent with the KCRV ranged from 0.3% to 0.6% using a mass balance approach and 0.5% to 1% using a qNMR method.The major analytical challenge posed by the material proved to be the detection and quantification of a significant amount of oligomeric organic material within the sample and most participants relying on a mass balance approach displayed a positive bias relative to the KCRV (overestimation of aldrin content) in excess of 10 mg/g due to not having adequate procedures in place to detect and quantify the non-volatile content—specifically the non-volatile organics content—of the comparison sample.There was in general excellent agreement between participants in the identification and the quantification of the total and individual related structure impurities, water content and the residual solvent content of the sample.The comparison demonstrated the utility of 1H NMR as an independent method for quantitative analysis of high purity compounds. In discussion of the participant results it was noted that while several had access to qNMR estimates for the aldrin content that were inconsistent with their mass balance determination they decided to accept the mass balance result and assumed a hidden bias in their NMR data. By contrast, laboratories that placed greater confidence in their qNMR result were able to resolve the discrepancy through additional studies that provided evidence of the presence of non-volatile organic impurity at the requisite level to bring their mass balance and qNMR estimates into agreement.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 ...
Recebido em 2/6/11; aceito em 8/12/11; publicado na web em 23/3/12Bioethanol is a strategic biofuel in Brazil. Thus, a strong metrological basis for its measurements is required to ensure the quality and promote its exportation. Recently, Inmetro certified a reference material for water content in bioethanol. This paper presents the results of these studies. The characterization, homogeneity, short-term stability and long-term stability uncertainty contributions values were 0.00500, 0.0166, 0.0355 and 0.0391 mg g −1 , respectively. The certificated value for water content of bioethanol fuel was (3.65 ± 0.11) mg g −1 . This CRM is the first and up to now the unique in the world.
Abstract:This study simulated the transport and storage conditions of ethanol in water certified reference material (CRM) produced by the Chemical Metrology Division of Inmetro -DQUIM with the purpose to estimate the measurement uncertainty related to stability. The short-term stability study was performed on five different concentrations in terms of g ethanol/100g solution (%) of the ethanol in water CRM: 0.0509%, 0.0890%, 0.1145%, 0.3820% and 0.4960%, at the temperatures of 4 ºC and 60 ºC. On the other hand, the longterm stability study was developed on four different concentrations: 0.0509%, 0.0890%, 0.1145% and 0.4960%. In this paper will be shown data from the long-term stability study concerning 20 weeks.The method used complies with ISO GUIDE 35, BCRGuideline for Feasibility Studies and ISO GUIDE 34.According to the statistical parameters used in both studies the stability of the ethanol in water CRM was confirmed for all concentrations studied.
This paper describes the studies performed with the candidate Certified Reference Material (CRM) of captopril, the first CRM of an active pharmaceutical ingredient (API) in Brazil, including determination of impurities (organic, inorganic and volatiles), homogeneity testing, short- and long-term stability studies, calculation of captopril content using the mass balance approach, and estimation of the associated measurement uncertainty.
Coulometric Karl Fischer (KF) titration is a highly accurate technique employed for moisture determination in non-aqueous solvents. Methodology for coulometric titration in a KF apparatus coupled to an autosampler oven was optimized in order to improve the accuracy of moisture determination in biodiesel derived from soybean. Several parameters were investigated, and three of them were optimized according to a central composite 23 star experimental design. The highest accuracy for moisture determinations corresponded to a relative standard deviation of 1.48 %. It was reached when the KF titrator was operated with electrode without diaphragm, the sample mass was 4 g, and the oven temperature was set to 170°C. Other parameters, like carrier gas flux and extraction time, presented minimal or no effects for improving the accuracy of moisture determination.
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