ABSTRACT Mixture designs are becoming frequently used as a powerful tool in modern chemical research. Their versatility opens the door to countless applications, making it a must-have tool in any experimental environment. Mixture designs combined with mathematical regressions allow us to understand how component proportions affect a measured response leading to system optimization at minimum cost and providing an accurate description of system behaviour. Dedicated software is often used to perform data analysis in mixture design experiments, but many of them are only commercially available hindering the use of mixture designs by scientific groups. The availability of free software would make these designs even more attractive, allowing users to benefit from the creative potential of this toolset without the prohibitive cost of proprietary tools. RStudio and LibreOffice are some of the free software with the capability to perform the necessary data analysis accompanying mixture designs. To exemplify how mixture design analysis can be executed the book “Como Fazer Experimentos” was used as reference material. Both software presented good results and the potential to be used to perform data analysis for mixture design experiments. research applications musthave must have environment behaviour experiments groups attractive tools Como Experimentos material

Impressões digitais de folhas de Coffea arabica expostas à luz solar e autossombreadas colhidas na mesma planta, foram usadas para determinar as variações das concentrações dos metabólitos devido a diferentes ambientes de luz e fases fenológicas. Os rendimentos dos extratos nos solventes etanol, acetona, hexano e diclorometano, bem como as suas misturas são apresentados. Os maiores rendimentos para todas as folhas autossombreadas e expostas ao sol são obtidos com misturas binárias etanol-acetona. Análise de componentes principais (PCA) dos espectros de infravermelho com transformada de Fourier (FTIR) dos extratos indicam diferenças espectrais entre 2962-2828, 1759-1543 e inferiores a 1543 cm-1 que podem ser atribuídos a maiores concentrações de ésteres de ácidos graxos ou grupo éster em triglicerídeos, cafeína, ácidos clorogênicos e carboidratos, que são mais predominantes em folhas na fase de floração. Os espectros dos picos de cromatografia líquida de alta eficiência com detector UV de arranjo de diodos (HPLC-UV-DAD) dos extratos mostraram que folhas expostas ao sol apresentam absorções mais fortes para a cafeína, ácido clorogênico e teobromina. Experimentos confirmatórios para determinar a concentração de cafeína realizados com curvas de calibração UV, mostram que a cafeína de folhas expostas ao sol são cerca de duas vezes maior que as folhas autossombreadas na fase de floração. O conhecimento da quantidade de cafeína em folhas de Coffea arabica é de importância ecológica, já que plantas expostas ao sol parecem mais estressadas do que as autossombreadas para esta espécie. As concentrações lipídicas em folhas autossombreadas são quase o dobro daquelas expostas ao sol.

Fingerprints of self-shaded and sunlight-exposed leaves of the same Coffea arabica plant were obtained to determine metabolic concentration changes owing to different light environments and phenological stages. Leaf extract yields of the ethanol, acetone, dichloromethane and hexane solvents, as well as their statistical design mixtures, are reported. Highest yields are obtained with binary 1:1 ethanol-acetone mixtures for all sun-exposed and self-shaded leaves. Principal component analysis (PCA) of Fourier transform infrared (FTIR) spectra of leaf extracts indicate spectral differences between 2962-2828, 1759-1543 and below 1543 cm-1 that can be attributed to higher concentrations of fatty acid esters or the ester group in triglycerides, caffeine, chlorogenic acids and carbohydrates that are more prevalent in leaves of flowering plants. High-performance liquid chromatography with UV diode array detector (HPLC-UV-DAD) spectra of the chromatographic peaks for the extracts showed that sun-exposed samples contain stronger absorptions for caffeine, chlorogenic acid and theobromine. Confirmatory experiments carried out with reference UV calibration curves determined caffeine contents for sun-exposed leaves that are about double those for self-shaded leaves of flowering plants. Knowledge of leaf caffeine content in Coffea arabica is of ecological importance since sun-exposed conditions seem more stressful than self-shading ones for this species. Lipid concentrations in self-shaded leaves are almost double those that were sun-exposed.

Ten common doubts of chemistry students and professionals about their statistical applications are discussed. The use of the N-1 denominator instead of N is described for the standard deviation. The statistical meaning of the denominators of the root mean square error of calibration (RMSEC) and root mean square error of validation (RMSEV) are given for researchers using multivariate calibration methods. The reason why scientists and engineers use the average instead of the median is explained. Several problematic aspects about regression and correlation are treated. The popular use of triplicate experiments in teaching and research laboratories is seen to have its origin in statistical confidence intervals. Nonparametric statistics and bootstrapping methods round out the discussion.

Para a determinação dos teores de umidade de mel, a legislação brasileira adota o método refratométrico proposto pela AOAC. No entanto, em outro trabalho, os autores observaram que a cristalização interferia na medida do índice de refração quando a amostra de mel se encontrava cristalizada e, portanto, eram obtidos teores de umidade superestimados. A Comissão Européia de Mel (EHC) adota outro método refratométrico, que usa um pré-tratamento da amostra quando esta estiver cristalizada. Assim, o objetivo deste trabalho foi comparar a precisão destes métodos refratométricos por diferentes técnicas estatísticas e estabelecer então o procedimento mais adequado para a análise de umidade em mel. Os resultados da análise dos teste t no nível de 95,0% de confiança para os teores médios de umidade das amostras de méis sugeriram que existiam diferenças significativas entre os dois métodos refratométricos (AOAC e EHC) somente para as amostras cristalizadas. A análise dos desvios padrão pela aplicação do teste F e construção de intervalos de confiança mostrou que o método da EHC foi mais preciso que o da AOAC para amostras de méis cristalizados. Desta forma, pode-se sugerir a adoção pela legislação brasileira do método refratométrico da EHC, como método oficial por este não apresentar erros sistemáticos.

For the determination of the moisture contents of honey, the Brazilian legislation adopts the refractometric method proposed by AOAC. However, in other work, the authors observed that the crystallization interferes in the refractive index measurement when the honey sample if encountered crystallized and, therefore, moisture contents overestimated were obtained. The European Honey Commission (EHC), adopt other refractometric method that use a pre-treatment of sample when this one was crystallized. So, the objective of this work was to compare the precision of these refractometric methods by different statistical techniques and it establish thus the more adequate procedure for moisture analysis in honey. The results of t-tests analysis in the 95% confidence level for the average moisture contents of the honey samples suggested that there were significant differences between the two-refractometric methods (AOAC e EHC) only for the crystallized samples. The analysis of standard deviations by application of F-test and building of confidence intervals shown that the EHC method was more precise than the AOAC methodology for the crystallized honey samples. In this way, it may be suggested the adoption by Brazilian legislation of refractometric method of EHC, as official method, by this one not present systematic errors.

Errors are always present in experimental measurements so, it is important to identify them and understand how they affect the results of experiments. Statistics suggest that the execution of experiments should follow random order, but unfortunately the complete randomization of experiments is not always viable for practical reasons. One possible simplification is blocked experiments within which the levels of certain factors are maintained fixed while the levels of others are randomized. However this has a cost. Although the experimental part is simplified, the statistical analysis becomes more complex.

The results suggest that the two variables studied are significant and that they may be independently optimized. The material of the sample holder interferes with the incineration process only due to the amount of heat transfered. The sample holder volume aids diffusion of the atmosphere to the honey sample, minimizing the foaming effect. According to the results, for the thermogravimetric analysis of ash content in honey, sample holders of platinum or alumina of 150 µL are indicated.

O objetivo deste trabalho foi investigar os parâmetros tecnológicos relevantes no processo de estruturação de polpa concentrada de mamão (16ºBrix), utilizando um delineamento experimental associado a Metodologia de Superfície de Respostas. Os resultados do planejamento composto central utilizado mostraram que as variáveis pectina (x1) e alginato (x2) foram estatisticamente significativas para aumentar a firmeza de fruta estrutura de mamão. Foram realizados experimentos para confirmar as previsões do modelo matemático proposto para firmeza. As frutas estruturadas obtidas com os menores níveis de pectina (7g/kg) e alginato (7g/kg) apresentaram firmeza elevada, em torno de 3,2kg, cerca de 2,4 vezes maior que o valor previsto pelo modelo, provavelmente devido a variações no pH da polpa de mamão. Os resultados mostraram ser possível produzir fruta estruturada com teor elevado de polpa de mamão concentrada (672g/kg) e quantidade mínima de sacarose (364g/kg). O glicerol (x3) na concentração de 100g/kg suprimiu a atividade de água dos géis de polpa concentrada de mamão para 0,922. A secagem (60ºC/6h) sob vácuo (0,8kgf/kg) das frutas estruturadas minimizou o problema de adesividade superficial das frutas estruturadas e, concomitantemente, promoveu redução na atividade de água, para níveis de umidade intermediária, em torno de 0,860.

The objective of this study was to investigate the relevant technological parameters of the manufacturing process of restructured fruit made from concentrated papaya pulp (16ºBrix) using an experimental delineation method associated with the Surface Response Methodology. The results of the Central Composed Design utilized show that the effect of the variables pectin (x1) and alginate (x2) on the increase in firmness of the papaya fruit restructured is statistically significant. A series of experiments was conducted to confirm the values predicted by the mathematical model proposed for firmness. The restructured fruits produced with the lowest addition levels of pectin (7g/kg) and alginate (7g/kg) exhibited high firmness values of about 3.2kg. These values were approximately 2.4 times greater than the values for firmness predicted by the model, probably due to variations in the pH of the papaya pulps used in the experiments. The results showed that it is possible to manufacture restructured fruit using high levels of concentrated papaya pulp (672g/kg) and minimum amounts of sucrose (364g/kg). Glycerol (x3) used at the concentration of 100g/kg reduced the level of water activity of the concentrated papaya pulp gels to 0.922. Vacuum drying (60ºC/6h; 0.8kgf/kg) of the restructured fruits minimized the problem of surface adhesion and, at the same time, lowered water activity to intermediate levels of about 0.860.

Selectivity studies for the determination of Cr(VI) using the catalytic oxidation of the o-dianisidine by hydrogen peroxide showed two distincts situations. In the first, when interferents were studied by a univariate procedure, Cr(III) and Cu(II) cause serious interferences even at the 2:1 proportion, relative to Cr(VI), while Fe(III) interfered at the 15:1 ratio and EDTA at the 10:1 ratio. On the other hand, when a multivariate investigation was performed, Cr(III) did not present any significant principal effects and its significant interaction effects were negative, in contrast to EDTA, that presented positive interaction effects although, like Cr(III), did not show significant interaction effects. In view of the interferent's action it become necessary to separate Cr(VI) by extraction with methylisobutylketone in a chloridric acid medium before its determination in vegetals and in wastewater from a cellulose industry samples. Using this procedure, the method precision is ±0,5% at the 10 ng/mL Cr(VI) concentration level. The detection and quantification limits, calculated by means of absorbance measurements of ten replicates of blank reagents were 1,1 and 3,2 ng/mL, respectively. The results obtained with real samples showed a relative standard deviation between 1,2% and 3,0% relative to their reference values.