Dissolução eletrolítica para a determinação de elementos de liga em aço ferramenta por ICP-AES

Different methods have been applied to solve special problems of metal analysis. First, the solid samples of tool steels were analyzed by X-ray fluorescence. Alternatively, an on-line electrodissolution implemented in a flow injection system and conventional dissolution procedure for determination of W, Mo, V and Cr in tool steels by ICP-AES is described. The resulting analyte solutions were compared with conventional dissolution procedure and determination by ICP-AES. The electrolytic procedure presented a good performance characterized by a sample throughput of 164 determinations per hour. Results were in agreement with those obtained by conventional acid dissolution.

Compostos de mercúrio. Revisão de métodos de determinação, tratamento e descarte

This review article on mercury compounds deals with the differences on toxicity of different forms of this metal, the Brazilian regulation for its disposal and the usual methods of determination. Besides that, the text gives special emphasis on the methods used for the treatment and disposal of residues containing mercury, as well as the new developments being made in this area.

Determinação condutométria de carbonato residual do calcário aplicado no solo por análise em fluxo

The objective of this study was to evaluate a flow injection system for determination of residual CO3(2-) in soil amended with lime material. It was used a closed system were the CO2 released from soil sample acidified with 0.5 mol L-1 HCl was capted in a 0.2 mol L-1 NaOH solution. After 16h the capted CO2 was determined by conductivimetry using a flow injection system. The results obtained by the proposed method were significantly correlated with those reported in soil samples used by the International Soil Analytical Exchange Programe. The regression equation was: y = 0.987x -- 0.075 r = 0.996, P > 0.01. For acid soils amended with CaCO3 the method showed a deviation error of 2.7%, detection limit was 0.077 mmol kg-1 of CO3(2-), and a recovery of 99.7% of the total CO3(2-) added in soil sample. The method was easily adapted for routine determination of residual CO3(2-) in soil samples with an analytical frequency of 40 samples per hour.

Determinação da estrutura molecular do ciclooctano por métodos ab initio e difração de elétrons na fase gasosa

The determination of the molecular structure of molecules is of fundamental importance in chemistry. X-rays and electron diffraction methods constitute in important tools for the elucidation of the molecular structure of systems in the solid state and gas phase, respectively. The use of quantum mechanical molecular orbital ab initio methods offer an alternative for conformational analysis studies. Comparison between theoretical results and those obtained experimentally in the gas phase can make a significant contribution for an unambiguous determination of the geometrical parameters. In this article the determination of the molecular structure of the cyclooctane molecule by electron diffraction in the gas phase and ab initio calculations will be addressed, providing an example of a comparative analysis of theoretical and experimental predictions.

Determinação espectrofotométrica de vitamina B2 (riboflavina) em formulações farmacêuticas empregando sistema de análises por injeção em fluxo

A flow injection spectrophotometric procedure exploiting merging zones is proposed for determining vitamin B2 (riboflavin) in pharmaceutical preparations. The determination is based on the red-colored complex formation between vitamin B2 and silver(I) which was measured at 520 nm. Vitamin B2 was determined in four pharmaceutical preparations in the 1.0 to 50.0 mg L-1 concentration range, with a detection limit of 0.5 mg L-1. The recovery from three samples ranged from 98.0 to 104.0 %. The analytical frequency was 42 h-1 and r.s.d. were lower than 1% for solutions containing 10.0, 30.0 and 50.0 mg L-1 vitamin B2 (n= 10). The results obtained in commercial formulations using the FIA procedure were in good agreement with those obtained by using a conventional fluorimetric procedure (r=0.9998) and also with the label values (r= 0.9997).

Avaliação dos métodos analíticos para a determinação de metabólitos do benzeno como potenciais biomarcadores de exposição humana ao benzeno no ar

Increasing attention is being paid to the use of biomarkers for determining the exposure of humans to air toxics. Biomarkers include the nonreacted toxic substance, their metabolites, or the reaction products of these toxics with naturally substances in the body. Significant progress has been made in the measurement of biomarkers during the past several years. Much of this progress has been because of the development of advanced analytical techniques for identification and quantification of the chemical species in complex matrix, such as biological fluids. The assessment of the potential cancer risk associated with exposure to benzene at occupational and non-occupational ambient is necessary because of the toxicological implications of this air pollutant. Thus, in this review, the analytical methodologies used to determine the benzene metabolites, in special, urinary muconic acid and S-phenylmercapturic acid, are described and several problems affecting the precision of these procedures are discussed. Finally, in view of the difficulty pointed out for selecting the more adequate biomarker, further studies to evaluate the human exposure levels to benzene should be done.

Métodos de extração e/ou concentração de compostos encontrados em fluidos biológicos para posterior determinação cromatográfica

When organic compounds present in biological fluids are analysed by chromatographic methods, it is generally necessary to carry out a prior sample preparation due the high complexity of this type of sample, especially when the compounds to be determinated are found in very low concentrations. This article describes some of the principal methods for sample preparation in analyses of substances present in biological fluids. The methods include liquid-liquid extraction, solid phase extraction, supercritical fluid extraction and extraction using solid and liquid membranes. The advantages and disadvantages of these methods are discussed.

Biossensores amperométricos para determinação de compostos fenólicos em amostras de interesse ambiental

Phenols are widely used in many areas and commonly found as industrial by-products. A great number of agricultural and industrial activities realise phenolic compounds in the environmental. Waste phenols are produced mainly by the wood-pulp industry and during production of synthetic polymers, drugs, plastics, dyes, pesticides and others. Phenols are also released into the environmental by the degradation of pesticides with phenolic skeleton. The phenols level control is very important for the environmental protection. Amperometric biosensor has shown the feasibility to complement laboratory-based analytical methods for the determination of phenolic compounds, providing alternatives to conventional methods which have many disadvantages. This brief review considers the evolution of an approach to amperometric measurement using the catalytic properties of some enzymes for phenolic compounds monitoring.

Comparação entre injeção na coluna ("on-column") e headspace dinâmico na determinação de benzeno, tolueno e xilenos (BTX) em amostras de água

The analysis of water samples containing volatile organic compounds has become an important task in analytical chemistry. Gas chromatography has been widely used for the analysis of volatile organic compounds in water. The headspace analysis shows as a principal characteristic the possibility of determination of the volatile components in drinking water. Benzene, Toluene and Xylene (BTX) are important compounds usually present in drinking water, from contamination by petroleum derivatives. Since they are toxic compounds even when present in low concentration levels, their determination is important in order to define the quality of the water. The sampling technique using headspace, coupled with gas chromatography as the separation method, showed to be suitable for BTX analysis in several samples at the mug/L (ppb) level.

Sistema em fluxo para determinação espectrofotométrica de uréia em plasma de sangue animal empregando leguminosa como fonte natural da enzima urease

A spectrophotometric flow injection analysis (FIA) procedure employing natural urease enzyme source for the determination of urea in animal blood plasma was developed. Among leguminous plants used in the Brazilian agriculture, the Cajanus cajan specie was selected as urease source considering its efficiency and availability. A minicolumn was filled with leguminous fragments and coupled to the FIA manifold, where urea was on-line converted to ammonium ions and subsequently it was quantified by spectrophotometry. The system was employed to determine urea in animal plasma samples without any prior treatment. Accuracy was assessed by comparison results with those obtained employing the official procedure and no significant difference at 90 % confidence level was observed. Other profitable features such as an analytical throughput of 30 determinations per hour, a reagent consumption of 19.2 mg sodium salicylate, 0.5 mg sodium hipochloride and a relative standard deviation of 1.4 % (n= 12) were also obtained.

Alternativas analíticas para determinação de ferro e titânio em cimento Portland

In the present work four different analytical methodologies were studied for the determination of iron and titanium in Portland cement. The cement samples were dissolved with hot HCl and HF, being compared Fe and Ti concentrations through four analytical methods: molecular absorption spectrophotometry using the reagents 1,2-hydroxybenzene-3,5-disulfonic acid (Tiron) and the 5-chloro-salicylic acid (CSA), inductively coupled plasma atomic emission spectrometry (ICP-AES) and flame atomic absorption spectrophotometry (FAAS). In the spectrophotometric determinations were studied pH conditions, reagents addition order, interferences, amount of reagents, linear range and stability of the system. In the techniques of ICP-AES and FAAS were studied the best lines, interferences, sensibility and linear range. The obtained results were compared and the agreement was evaluated among the methods for the determination of the metals of interest.

Determinação simultânea de cátions por eletroforese capilar: fundamentos e aplicações

In this work, the analysis of cations by capillary electrophoresis is reviewed from the theoretical and practical point of view. Separation mechanisms and detection modes are discussed and illustrated. A thorough compilation of the literature over the last ten years, regarding applications of the technique to the analysis of cations in real matrices, is presented.

Qualidade de medições em química analítica. Estudo de caso: determinação de cádmio por espectrofotometria de absorção atômica com chama

Calculation of uncertainty of results represents the new paradigm in the area of the quality of measurements in laboratories. The guidance on the Expression of Uncertainty in Measurement of the ISO / International Organization for Standardization assumes that the analyst is being asked to give a parameter that characterizes the range of the values that could reasonably be associated with the result of the measurement. In practice, the uncertainty of the analytical result may arise from many possible sources: sampling, sample preparation, matrix effects, equipments, standards and reference materials, among others. This paper suggests a procedure for calculation of uncertainties components of an analytical result due to sample preparation (uncertainty of weights and volumetric equipment) and instrument analytical signal (calibration uncertainty). A numerical example is carefully explained based on measurements obtained for cadmium determination by flame atomic absorption spectrophotometry. Results obtained for components of total uncertainty showed that the main contribution to the analytical result was the calibration procedure.

Determinação de baixas concentrações de cobre em águas naturais por espectrofotometria de absorção atômica em chama usando um sistema SIA com uma coluna de poli(etilenimina)

This paper describes a sequential injection analysis (SIA) set-up coupled to a flame atomic absorption spectrometer (FAAS) to accomplish the determination of low concentrations of copper in drinking waters. Copper is first retained under neutral media in an on-line 29x1.6 mm column filled with poly(ethylenimine) immobilised on silica gel. The retained analyte is then eluted by flowing through the column 250 mL of a nitric acid solution. The selection of 3.85 ml of sample enabled to obtain a detection limit of 0.27 mug/L and a sampling rate of about 24 samples/h. There was a good agrement between the results of 12 samples furnished by the proposed procedure and by electrothermal atomic absorption spectrometry. Repeatability assessment gave a relative standard deviation of 1.3 % after ten replicate analysis of a sample containing about 70 mug/L in copper..

Deposição eletrolítica catódica e anódica simultâneas para minimizar interferências de cobre e chumbo na determinação espectrofotométrica de cádmio em água e alimentos via reação com Verde de Malaquita e iodeto

Simultaneous electrolytic deposition is proposed for minimization of Cu2+ and Pb2+ interferences on automated determination of Cd2+ by the Malachite Green-iodide reaction. During electrolysis of sample in a cell with two Pt electrodes and a medium adjusted to 5% (v/v) HNO3 + 0.1% (v/v) H2SO4 + 0.5 mol L-1 NaCl, Cu2+ is deposited as Cu on the cathode, Pb2+ is deposited as PbO2 on the anode while Cd2+ is kept in solution. With 60 s electrolysis time and 0.25 A current, Pb2+ and Cu2+ levels up to 50 and 250 mg L-1 respectively, can be tolerated without interference. With on-line extraction of Cd2+ in anionic resin minicolumn, calibration graph in the 5.00 - 50.0 µg Cd L-1 range is obtained, corresponding to twenty measurements per hour, 0.7 mg Malachite Green and 500 mg KI and 5 mL sample consumed per determination. Results of the determination of Cd in certified reference materials, vegetables and tap water were in agreement with certified values and with those obtained by GFAAS at 95% confidence level. The detection limit is 0.23 µg Cd L-1 and the RSD for typical samples containing 13.0 µg Cd L-1 was 3.85 % (n= 12).