Search

The result of a chemical measurement is consequence of a set of steps that begins with sample selection. The aim of this study was to evaluate the relative importance of the sampling in overall measurement uncertainty, taking as study case physicochemical measurements of diesel. The empirical method used was by duplicates, and the treatment of data sets was performed by four different statistical techniques: classic analysis of variance, robust analysis of variance and two different Range Statistics models. The choice must be backed by previous evaluation of data set in terms of normality, independence, presence of outliers and homogeneity of variance. It was found that Range Statistics produced most reliable results under different premises and for the variety of physicochemical parameters evaluated. Robust analysis of variance failed indicates proper influence of sampling even it is a test designed to work under the lack of some of the proper premises.

In any commercial transaction, the presence of tolerances from specification limits is essential to ensure that the true value of the property of interest is sufficiently close to the specification value with a mutually agreed probability, so that there is no litigation between the parties. In order to meet this requirement, this tolerance is treated elegantly as a “toast” or more technically as a superior quality that the customer receives—giveaway. This work presents a new methodology for determining the tolerance limits of critical properties in some fuels, based on the reproducibility, on the difference between the averages of all acceptable results of each laboratory and on the specifications derived from the Brazilian National Agency for Oil, Natural Gas and Biofuels. Applying this approach to flash point by tag closed, final boiling point, volatility (95 % evaporated temperature), electrical conductivity and total sulfur content of some fuels and by means of a hypothesis test, the results show that this methodology was validated for most of the proposed new limits.

Ractopamine is used as an animal feed additive, but its adverse effects led to the necessity of the current monitoring programs of ractopamine residues in food products, so its reliable quantification is indispensable. This work aims to demonstrate the stability of solutions of ractopamine used for calibration of a liquid chromatography–tandem mass spectrometry method. Naturally contaminated samples with ractopamine were quantified using solutions prepared on different days. The stability study was based on an empirical model that considered a straight line (slope = 1) to describe the degradation mechanism. No significant change in the slope was detected. It could be concluded that solutions underpinning calibration curves at two different working intervals were stable for at least 11 months and 5 months, respectively.

Literature describes several procedures based on statistical principles to validate whether the degree of agreement between the results produced by a stream analyzer system—systems for determining chemical and physical characteristics by continual sampling, automatic analysis, and recording or otherwise signaling of output data—and those produced by an independent test measurement procedure, which purports to measure the same property, meets user-specified requirements. However, these documents always consider that the data gathered during validation procedure are normally distributed, and this supposition it is not always true. The aim of this manuscript is to develop four different procedures applied to data with nonparametric behavior. The most representative validation procedure compares measures of position and dispersion, using typical process samples, while the less representative one compares only measures of position, using a reference sample. These nonparametric data are also treated using parametric statistics for comparison. The results show that different conclusions can be reached when the nonparametric data are treated as parametric. A new Brazilian standard is being carried out based on this subject, in order to complement the international standards.