Utilização do índice de retenção linear para caracterização de compostos voláteis em café solúvel utilizando GC-MS e coluna HP-Innowax

Gas chromatography coupled with mass spectrometry (GC-MS) is widely used for the characterization of volatile compounds. However, due to the complexity of the soluble coffee matrix, a complete identification of the components should not be based on mass spectra interpretation only. The linear index of retention (LRI) is frequently used to give support to mass spectra. The aim of this work is to investigate the characterization of the volatile compounds in soluble coffee samples by GC-MS using LRI values found with a HP-INNOWAX column. The method used allows a significant increase of the reliability of identifying compounds.

Adaptación del Índice de Bienestar Personal para adolescentes en lengua española y portuguesa

The psychometric properties of the Personal Wellbeing Index are analyzed on a Spanish and Portuguese adolescent sample. We test the reliability of the scale using Cronbach’s alpha. And complementarily we analyze the item-total correlations in the different wellbeing domains included. We execute an exploratory factor analysis (principal components) and a multigroup Confirmatory Factor Analysis (CFA). The results show that Cronbach’s alpha is 0.79 for the Chilean version and in the Brazilian version is 0.78 confirming adequate levels of reliability found in previous studies. Correlations between fields of well-being shows values ranging between 0.224 and 0.496 for Chile and from 0.24 to 0.46 for Brazil. The results are similar to those obtained in other countries. The monofactorial structure of the scale is cinfirmed, also the adjustment to the scale structure to the data of the two samples and the comparability of means of global indices. The results suggest the existence of other well-being domains that had not been considered in the original proposal of the scale

Autoamostrador de baixo custo para análise por injeção em fluxo

This paper describes a homemade autosampler for flow injection analysis (FIA), constructed with two step motors from old floppy disk drives (5¼-inch). The autosampler was connected to a computer through the parallel port and the sampling process was controlled by software in Quick Basic. The performance of the system was assessed by the determination of ammonium, based on the gaseous diffusion into a bromocresol purple solution, following the spectrophotometric determination of change in absorbance. The easy and simple construction is the main characteristics of this equipment and analytical results with RSD lower than 1% were obtained.

Construção de um calorímetro isotérmico diferencial de alta sensibilidade e baixo custo

The high cost of sensitivity commercial calorimeters may represent an obstacle for many calorimetric research groups. This work describes the construction and calibration of a batch differential heat conduction calorimeter with sample cells volumes of about 400 μL. The calorimeter was built using two small high sensibility square Peltier thermoelectric sensors and the total cost was estimated to be about US$ 500. The calorimeter was used to study the excess enthalpy of solution of binary mixtures of liquids, as a function of composition, for the following binary systems of solvents: water + 1,4-dioxane or + dimethylsulfoxide at 298,2 ± 0,5 K.

Oxidação do borneol à cânfora com água sanitária - um experimento simples, de baixo custo e limpo

Regulatory pressure is increasingly focusing on the use and disposal of substances hazardous to human health and environment. In the last years efforts have also been made to introduce green chemistry concepts in undergraduate courses. In this paper we present an experiment on the oxidation reaction of borneol to camphor with bleach in acetone. This experiment is important to show undergraduate students that a cheap and non hazardous commercial product can be a useful oxidation agent of alcohols.

Desenvolvimento e avaliação de um porta-amostra de baixo custo para caracterização elétrica de materiais cerâmicos

Conventional sample holder cells used to the electric characterization of ceramics at high temperature consists of an alumina tube and platinum wires and plates using a complex design. The high cost materials used in the conventional sampler holder cell were replaced by stainless steel and conventional ceramics. The sample holder was validated by characterizing yttria-stabilized-zirconia in a temperature range of 25 to 700 ºC. The results do not present variations, discontinuity or unusual noise in the electric signals. Several samples were characterized without maintenance, which demonstrates that the sample holder is electric and mechanic adequate to be used to electrical characterization of ceramics up to 700 ºC.

Hidróxido de níquel suportado em carbono: um catalisador de baixo custo para a eletro-oxidação de alcoóis em meio alcalino

The present manuscript shows the synthesis of nickel hydroxide supported in carbon (Ni(OH)2/C) as a alternative material for catalytic alcohol oxidation in alkaline medium. The Ni(OH)2/C was synthesized in different percentage using a sonic bath. No current densities variation during successive cyclic voltammetry experiments was observed. The Ni(OH)2/C electrodes exhibit a potent and persistent electrocatalytic activity towards the oxidation of different alcohols. In addition, alcohols electooxidation occurs in less positive potential compared with noble metal catalyst.

Construção de uma célula de gás de baixo custo para análise no infravermelho

Infrared spectroscopy is a versatile technique used for qualitative and quantitative determination of all types of molecular species. As far as analysis of confined or flowing gases is concerned, different types of cell can be found in the market, but they are often very expensive. This study describes the construction of a very efficient gas cell with good reproducibility for qualitative infrared analysis of confined or flowing gases, using easily available and low-cost materials.

Capacidade de oxidação como índice de estabilidade da matéria orgânica de sedimentos de acordo com gradiente fluvial-estuarino do rio Paraíba do Sul

The hummus composition and it redox properties have been used to evaluate the organic matter quality from natural systems. The objectives of this study were the fractionation of the organic matter and the determination of the oxidation capacity of humic acids to evaluate the organic matter quality of sediments from a gradient fluvial-estuarine in the Brazilian Southeast. The carbon/nitrogen and humic acid/fulvic acid relationships of the organic matter and of the oxidation capacity of humic acids were positively correlated and followed the order: estuarine bordered mangroves ≅ fluvial bordered urban center and pasture > estuarine bordered pasture ≅ marine.

Craqueamento termo-catalítico da mistura óleo de fritura usado-lodo de estamparia têxtil para a produção de óleo com baixo índice de acidez

In this work, cracking experiments were performed to carry out the thermal conversion of the mixture of used frying oil and textile stamping sludge in continuous reactor. The textile stamping sludge was used to catalyze the reaction of thermal cracking. The physical and chemical properties of the oil produced were analyzed. Among the results of this analysis the level of acidity in the range of 12 mg KOH/g stands out. Low levels of acidity as this particular mean better quality oil. In this regard it is important that further researches on processes of conversion of residual oil occur.

Construção e aplicação de um minissensor de filme de bismuto utilizando materiais de baixo custo para determinações voltamétricas in loco

The construction of a low cost mini sensor containing a bismuth-film electrode (BiFE), as work electrode, a silver electrode as pseudo reference electrode, and copper as counter electrode is proposed. The application of this mini sensor using a low cost electrochemical cell for in loco voltammetric determinations of inorganic and organic analytes is also described.

Equipamento de baixo custo para extração em fase sólida em amostras aquosas de grande volume utilizando pressão positiva de N

Extraction/concentration is a crucial step for the analysis of organic compounds at trace level concentrations and dispersed in complex matrices. Solid-phase extraction (SPE) is one of the techniques used for this purpose. In this work, a low cost apparatus for SPE was developed that uses nitrogen under positive pressure and ensures the maintenance of the sample flow, while also allows the simultaneous extraction of different samples without cross-contamination and sample contact with plastic materials. For the system set up, easily accessible materials were used such as hypodermic needles, stainless steel tubes, rubber stoppers, and 3-way valves from serum delivery apparatus.

Aplicação da radiação ultravioleta como forma de contribuição para a química verde e construção de um reator fotoquímico alternativo e de baixo custo, para pré-tratamento de amostras

Ultraviolet radiation corresponds to a fraction of electromagnetic radiation, covering wavelengths between 1 and 400 nm. Methods based on UV irradiation have become popular because it is possible to treat samples simply by applying energy, avoiding procedures that require the use of toxic substances, thus contributing to the development of Green Chemistry. This study aimed to assess the main applications of UV radiation reported in the literature and thoroughly described the construction of an alternative and low-cost photochemical reactor to be used for the pretreatment of samples in the laboratory. The use of this new photochemical reactor in the clean-up of milk samples for spectrofluorimetric measurements was also reported.

Desenvolvimento de um sistema de análise por injeção em fluxo utilizando materiais alternativos de baixo custo para fins didáticos

This work describes a simple and inexpensive flow injection analysis system in which gravity force provides fluid propulsion while needles for insulin administration or metallic wires act as electrodes for amperometric detection. The proposed system was able to demonstrate the influence of several operational parameters on the transient signals. Moreover, this system was successfully used to evaluate both the stoichiometry of Cu2+-EDTA complex and the effect of pH on the kinetics of the reaction between ferricyanide and ascorbic acid. Therefore, the proposed system can be regarded as an efficient and accessible didactic tool for the teaching of FIA principles.