Métodos de extração para quantificação de manganês disponível em fertilizantes

The solubility of Mn in different fertilizers (MnSO4.H2O-p.a., MnO2-p.a.+MnO-Ind., MnO2-Ind.+MnO-Ind., MnO2-p.a., MnO2-Ind. and MnO-Ind.) was determined using different methodologies: total content and soluble contents in water, 10% H2SO4, citric acid at 20 g L-1, diluted neutral ammonium citrate, (1+9) and DTPA at 0.005 mol L-1. The Mn solubilities in the latter three extractors were assessed after agitation of the sample for one hour and after boiling for 5 minutes. The extraction procedure using neutral ammonium citrate (1+9), at 1:100, with agitation for one hour, was shown to be the most adequate to assess the availability of Mn in fertilizers.

Aplicação de métodos de calibração multivariada para a determinação simultânea de riboflavina (VB2), tiamina (VB1), piridoxina (VB6) e nicotinamida (VPP)

In this work, the artificial neural networks (ANN) and partial least squares (PLS) regression were applied to UV spectral data for quantitative determination of thiamin hydrochloride (VB1), riboflavin phosphate (VB2), pyridoxine hydrochloride (VB6) and nicotinamide (VPP) in pharmaceutical samples. For calibration purposes, commercial samples in 0.2 mol L-1 acetate buffer (pH 4.0) were employed as standards. The concentration ranges used in the calibration step were: 0.1 - 7.5 mg L-1 for VB1, 0.1 - 3.0 mg L-1 for VB2, 0.1 - 3.0 mg L-1 for VB6 and 0.4 - 30.0 mg L-1 for VPP. From the results it is possible to verify that both methods can be successfully applied for these determinations. The similar error values were obtained by using neural network or PLS methods. The proposed methodology is simple, rapid and can be easily used in quality control laboratories.

Estudo comparativo de métodos para a determinação da concentração de carbono em solos com altos teores de Fe (Latossolos)

Soil organic matter (SOM) plays an important role in physical, chemical and biological properties of soil. Therefore, the amount of SOM is important for soil management for sustainable agriculture. The objective of this work was to evaluate the amount of SOM in oxisols by different methods and compare them, using principal component analysis, regarding their limitations. The methods used in this work were Walkley-Black, elemental analysis, total organic carbon (TOC) and thermogravimetry. According to our results, TOC and elemental analysis were the most satisfactory methods for carbon quantification, due to their better accuracy and reproducibility.

Aplicação do ultra-som em sistemas eletroquímicos: considerações teóricas e experimentais

The aim of this review is to present and discuss the applications of ultrasound in electrochemical systems such as in sonoelectroanalysis and sonoelectrolysis for the electrochemical combustion of organic compounds. Initially, theoretical and experimental aspects are discussed, particularly those related to the enhancement of mass transport and the surface cleaning effects. Some results are included to illustrate alternative geometries for the experimental measurements and the working electrodes used in these systems. In the sequence, the available publications are presented and discussed to demonstrate that ultrasound combined with electrochemical techniques is a powerful set-up for the detection of analytes such as metals and/or organic compounds in hostile media and for the effective destruction of toxic organic substances. At the end, a table summarizes the results already published in the literature.

Planilha de validação: uma nova ferramenta para estimar figuras de mérito na validação de métodos analíticos univariados

This work presents the VALIDATION SPREADSHEET, a public domain tool that can be used to evaluate the figures of merit for univariate analytical methods. A real example of BTEX determination in environmental samples is included to illustrate its use. The spreadsheet has been developed for Excel® and Open Office®, and is available on the internet at http//lqta.iqm.unicamp.br.

Métodos de obtenção, reatividade e importância biológica de 4-tiazolidinonas

Molecules containing the 4-thiazolidinone ring are known to possess a wide range of biological properties including antimicrobial and anti-inflammatory activities among others. These compounds can be synthesized by cyclization reactions involving alpha-haloacetic acid or alpha-mercaptoacetic acid and employed in several chemoselective reactions. Comprehensive reviews have been written on 4-thiazolidinones in 1961 by Brown and in 1980 by Singh et al. In the recent literature, some new synthesis methods for 4-thiazolidinone derivatives and several reactions have been reported. These advances warrant to review the chemical and biological properties of compounds with this important heterocycle employed in synthetic organic chemistry and medicinal chemistry.

Validação de métodos cromatográficos por clae para análise das vitaminas B1, B2, B6 e niacina naturalmente presentes em farinha de cereais

Complex B vitamins are present in some cereal foods and the ingestion of enriched products contributes to the recommended dietary intake of these micronutrients. To adapt the label of some products, it is necessary to develop and validate the analytical methods. These methods must be reliable and with enough sensitivity to analyze complex B vitamins naturally present in food at low concentration. The purpose of this work is to evaluate, with validated methods, the content of vitamins B1, B2, B6 and niacin in five cereal flours used in food industry (oat, rice, barley, corn and wheat).

Influência de métodos de digestão e massa de amostra na recuperação de nutrientes em resíduos orgânicos

The influence of nitric-perchloric, aqua regia, dry ashing and microwave digestion methods, in combination with 100 and 200 mg of sample, on the characterization and recovery of nutrients in samples of sludge sewage, poultry, swine, quail and bovine manures, organic compost, organic substrate and humic material were studied. Nitric-perchloric digestion with 200 mg samples recovered the higher nutrient contents. The nitric-perchloric method recovered also low levels of K. Dry ashing caused S volatilization and microwave digestion produced dark color extracts and this impaired S determination. Aqua regia recovered the lowest contents of nutrients in the organic residues evaluated.

Métodos simples de formação de monocristal de substância orgânica para estudo estrutural por difração de raios X

This work presents three operationally simple laboratory protocols for monocrystal growth of small-molecule organic compounds, which have been applied with success in the last ten years for the formation of single crystals for X-ray structural studies. In addition, five structure hints were formulated as general guidelines for selecting a small-molecule organic compound as a candidate for monocrystal growth: molecular weight >200 D, melting point >100 ºC, two or more aromatic rings in the structure, at least two sites for intermolecular hydrogen bond formation, and a halogen or other heavy atom in the structure.

Métodos de amostragem e análise para compostos reduzidos de enxofre atmosférico

This work presents a review of sampling and analytical methods that can be applied to atmospheric traces of reduced sulphur compounds (RSC) in the atmosphere. Sampling methodology involving discontinuous methods with preconcentration is mostly used. For the most part, adsorption on solids and cryogenic capture are applied as a procedure. The analysis of these compounds has been done mainly by gas chromatography with FPD, fluorescence and spectrophotometry. Advantages and disadvantages of the methodologies are also mentioned in this paper, aiming to guide the reader towards the most appropriate choice of a sampling and analytical method for RSCs.

Validação de métodos cromatográficos para a determinação de resíduos de medicamentos veterinários em alimentos

Different agencies that supply validation guidelines worldwide establish almost the same parameters to be evaluated in the validation process of bioanalytical methods. However, they recommend different procedures, as well as establish different acceptance criteria. The present review delineates and discusses the stages involved in the validation procedures of bioanalytical methods designed for determining veterinary residues in food, explaining the main differences in the guidelines established for this purpose by the main regulatory agencies in the world.

Extração de β-caroteno de cenouras: uma proposta para disciplinas experimentais de química

This paper reports on the development of a simple and fast procedure for β-carotene extraction from carrots and its quantification by UV/Vis spectroscopy. Carotenoids extracted from carrots may also be used as alternative reagents for TLC (thin layer chromatography) detection of natural compounds with antioxidant properties, replacing the commercial p.a. grade β-carotene. Although this reagent had around 10% b-carotene, it proved to be as efficient for TLC analysis as the commercial p.a. grade β-carotene. This practice is a useful alternative for teaching undergraduate organic chemistry laboratory classes.

Contaminantes voláteis provenientes de embalagens plásticas: desenvolvimento e validação de métodos analíticos

Plastic packaging materials intended for use in food packaging is an area of great interest from the scientific and economic point of view due to the irreversible internationalization and globalization process of food products. Nevertheless, a debate related to food safety aspects has emerged within the scientific community. Therefore, the development of analytical methods that allow identifying and quantifying chemical substances of toxicological potential in the packaging is considered essential. This article focuses on the main analytical methods, including validation parameters, as well as extraction and quantification techniques for determination of volatile organic compounds from food packaging materials.

Validação de métodos para determinação de fluoxetina em cápsulas

A UV spectrophotometric method was developed and validated and a chromatographic method was adapted from the American Pharmacopeia for the analysis of Fluoxetine Hydrochloride capsules. Ethanol was used as solvent for the spectrophotometric method, with detection and determination at 276 nm. The separation for the chromatographic method was carried out using the reversed-phase column LC-8, triethylamine buffer, stabilizer free tetrahydrofuran and methanol (5:3.5:1.5), pH 6.0 as mobile phase and detection at 227 nm. The results obtained for both methods showed to be accurate, precise, robust and linear over the concentration range 100.00 - 300.00 µg/mL and 40.00 - 80.00 µg/mL of fluoxetine hydrochloride for the spectrophotometric and chromatographic methods, respectively. The accuracy of the methods was evaluated by a recovery test and showed results between 98.89 and 101.10%.

A toxicidade em ambientes aquáticos: discussão e métodos de avaliação

Aquatic toxicity tests are assays performed with different aquatic organisms of different ecological organization levels. Such tests are a source of information on the toxicity of a given substance or wastewater under controlled conditions, and they complement the physico-chemical analyses. Moreover, they allow one to evaluate the risks resulting from the presence of toxic substances in the environment. Algae, crustaceans, fishes and bacteria are frequently used in toxicity tests. In this work, we will present the main aspects related to the aquatic toxicity tests and a discussion of their applicability will also be presented.