Homogeneity study of a corn flour laboratory reference material candidate for inorganic analysis

Improvement of the characterization uncertainty of a matrix-certified reference material for accurate measurement of H2SiF6 mass fraction in industrial fluorosilicic acid by using a direct measurement procedure

The role of metrology in the industrial and manufacturing sectors is of paramount importance to ensure informed decision-making whether for product quality control, process monitoring and R&D activities. However, to guarantee the quality and reliability of analytical measurements, the development and use of appropriate reference materials (CRMs) is essential. In particular, certified reference materials (CRMs) are extensively used to validate analytical methods in a multitude of applications, measure uncertainty, improve the accuracy of measurement data, as well as to establish the meteorological traceability of analytical results. In this paper, we report the improvement of the characterization uncertainty of an in-house matrix reference material by direct determination of the concentration of fluorosilicic acid recovered from the fertilizers production industry. The certified reference material was characterized by the potentiometric method as a novel and direct approach for the determination of H2SiF6 concentration and the results were compared against a reference measurement procedure based on molecular absorption spectrophotometry (UV-VIS). The approach adopted in the work resulted in the improvement of the uncertainty of the CRM by decreasing the characterization uncertainty, which constitutes the major contribution to the overall uncertainty. The newly obtained characterization combined standard uncertainty was 2.0 g.kg-1, which gives an expanded uncertainty (k = 2 with a confidence interval of 95%) of the CRM of 6.3 g.kg-1 instead of 11.7 g.kg-1 reported in previous works. This improved CRM can be used to improve the uncertainty of the analytical methods used for the determination of H2SiF6 mass fraction and, therefore, to improve the accuracy of measurement data.

Homogeneity and stability assessment of a candidate to pumpkin seed flour reference material by means of computer vision based chemometrics assisted approach

This study proposes a preliminary assessment of the homogeneity and stability through digital image acquisition of a candidate for mechanically processed pumpkin seed meal reference material, exploring the concepts of homogeneity curve and the analysis of texture characteristics by Continuous-Level Moving Block through Robust Principal Component Analysis. This innovative methodology allowed us to examine the percentage of homogeneity in a set of samples, revealing an average of 41% with only one outlier in relation to the entire sample, indicating low homogeneity. In the stability study carried out after storing samples for 12 months at different temperatures, 83% of the samples were considered regular and 17% were outlier, which means that most of them were considered stable. Therefore, this methodology is useful for screening samples for homogeneity, by textural analysis, and detected non-homogeneity can be corrected in advance for quantification by standard protocols.

The use of ANOVA-PCA and DD-SIMCA in the development of corn flour laboratory reference materials

The development of a collaborative study as a requirement for the preparation of a laboratory reference material candidate is reported in this paper. The evaluation was performed by 13 laboratories invited to quantify the calcium, potassium, magnesium, phosphorus, copper, iron, manganese and zinc; 8 of them presented results for all the analytes under investigation. The data were statistically analyzed by applying the z-score robust technique as recommended by ISO Guide 35. For the potassium element, laboratories 4 and 13 presented questionable results. Laboratory 5 proved to be unsatisfactory for calcium and zinc. ANOVA-PCA and DD-SIMCA were also applied to evaluate stability and interlaboratory studies results, respectively. It has been demonstrated that multivariate data analysis can be successfully applied as an alternative method to the recommendations made by ISO 13528 and ISO Guide 35 with defined confidence intervals.

Fast method to determine the elements in maize flour: reduction in preparation time and reagent consumption

Abstract The aim of this work was to develop and validate methodology to reduce the digestion time and reagent consumption in the determination of minerals in maize flour. The standard methodology employed in Brazil is that described by AOAC. It consists of the calcination of the sample at high temperatures for a long period of time, making the process expensive and slow. In this work, a wet sample digestion method using HNO3 was employed, heating on a block digester with final dissolution in an ultrasonic bath. The validation tests involved linearity and working range studies, and the determination of the detection and quantification limits, accuracy and precision. The sample digestion time was 1:30 h and the percent recoveries for the metals were 93% for Ca, 98% for Cu, 110% for Fe, 97% for Mg, 101% for Mn and 106% for Zn.

Exploration of optical fibres as a carrier for new benzene and toluene matrix-free reference materials

To meet high expectations concerning precision and accuracy of reference materials, preparation of matrix-free reference materials using thermal decomposition-gas chromatography-mass spectrometry (TD-GC-MS) was proposed in this study. In the paper, the results obtained in preparation of the new reference materials for benzene and toluene are presented, based on the thermal decomposition technique of compounds chemically bound to the surface of optical fibre segments. The results obtained at various stages of the research procedure (homogeneity, stability) confirmed the possibility of using prepared laboratory samples of materials as reference materials for benzene and toluene. For the prepared batch of materials, reference values 1.26 ± 0.91 (ng/fibre) for benzene and 11.3 ± 7.4 (ng/fibre) for toluene were determined.