A simple, sensitive and reliable method for the separation, preconcentration and determination of ultra trace amounts of chromium species has been developed. Chromium(VI) in aqueous sample was reacted with 9-phenyl-2,3,7-trihydroxy-6-fluorone to produce a chelate at pH of 5.0 and extracted onto the magnetic nanoparticles coated with the ionic liquid 1-hexadecyl-3- methylimidazolium bromide. The trapped analyte was back extracted using 350 µL of nitric acid solution (2 mol L-1) and was determined by electrothermal atomic absorption spectrometry. Total chromium was determined by oxidizing CrIII to CrVI using KMnO4 in acidic media. Under the optimum conditions, the method exhibited a linear dynamic range of 0.01-0.50 µg L-1 with an enhancement factor of 112 and a detection limit of 0.003 µg L-1 for CrVI. The coefficient of variation (n = 6) at 0.3 µg L-1 concentration level of CrVI was 3.2%.

A simple and sensitive spectrophotometric method is proposed for the simultaneous determination of protocatechuic acid and protocatechuic aldehyde. The method is based on the difference in the kinetic rates of the reactions of analytes with [Ag(NH3)2]+ in the presence of polyvinylpyrrolidone to produce silver nanoparticles. The data obtained were processed by chemometric methods using principal component analysis artificial neural network and partial least squares. Excellent linearity was obtained in the concentration ranges of 1.23-58.56 µg mL-1 and 0.08-30.39 µg mL-1 for PAC and PAH, respectively. The limits of detection for PAC and PAH were 0.039 and 0.025 µg mL-1, respectively.

Silver ion imprinted polymer (IIP) was synthesized in the presence of Ag(I)-N,N’‑bis(salicylidene)ethylenediamine (salen) complex using 4-vinylpyridine as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the crosslinker, and 2,2-azobis(isobutyronitrile) (AIBN) as the initiator. The Ag(I)-imprinted polymer (IIP) particles were characterized by SEM (scanning electron microscope), FTIR (Fourier transform infrared spectroscopy) and BET/BJH (Brunauer-Emmett-Teller/Barrett-Joyner-Halenda) analysis. The imprinted Ag(I) ions were completely removed by leaching the IIP with thiourea (0.5 mol L-1). The polymer was employed as a selective sorbent for extraction and separation of the trace amounts of the Ag(I) ions. The preconcentrated ion was determined via the flame atomic absorption spectrometry (FAAS) or it was reduced to silver nanoparticles and quantified by spectrophotometry based on its localized surface plasmon resonance peak (LSPRP). The figures of merit of both methods were compared. Under the optimized conditions, a sample volume of 80 mL resulted in an enhancement factor of 312. The detection limit (3Sb/m) and the relative standard deviation (n = 10) at 10 µg L-1 level for FAAS were found to be 0.06 µg L-1, 2.9%, whereas for the LSPRP method they were 0.5 µg L-1 and 10.3%, respectively. The methods were successfully applied to the determination of silver in radiology film, hair, nails, and water samples.

O cádmio de uma amostra aquosa foi quantitativamente adsorvido em uma microcoluna empacotada com cadion imobilizado em nanopartículas de TiO2 recobertas por dodecilsulfato de sódio. O cádmio retido foi eluido com uma solução de ácido clorídrico 2,5 mol L-1 e medido por espectroscopia de absorção atômica com vapor frio (CVAAS). As influências de diferentes variáveis, como pH, taxas de fluxo da amostra e do eluente, quantidade do sorvente e volume da amostra, na recuperação do cádmio foram investigadas. Sob condições ótimas, um volume de 200 mL de amostra resultou em um fator de pré-concentração de 100. A precisão (RSD%, n = 8) em 0,05 µg L-1 de cádmio foi 3,6% e o limite de detecção, baseado em três vezes o desvio padrão do branco (3Sb), foi de 1,3 ng L-1. O método foi aplicado com sucesso à determinacão de cádmio em amostras de arroz, peixe, leite e água.

Cadmium was quantitatively adsorbed from aqueous sample onto a microcolumn packed with cadion immobilized on sodium dodecyl sulfate-coated TiO2 nanoparticles. The retained cadmium was eluted with 2.5 mol L-1 hydrochloric acid solution and measured by cold vapor atomic absorption spectrometry (CVAAS). The influences of different variables such as pH, sample and eluent flow rates, amount of the sorbent and volume of the sample on the recovery of cadmium were investigated. Under the optimum conditions, a sample volume of 200 mL resulted in a preconcentration factor of 100. The precision (RSD%, n = 8) at the 0.05 µg L-1 level of cadmium was 3.6% and the limit of detection based on three times the standard deviation of blank solution (3Sb) was 1.3 ng L-1. The method was successfully applied to the determination of cadmium in rice, fish, milk, and water samples.

Neste estudo, um método simples e barato de microextração líquido-líquido dispersiva com solidificação da gota orgânica flutuante (DLLME-SFOD) foi desenvolvido para separação e especiação de Se inorgânico previamente à sua determinação espectrofotométrica. O método está baseado na formação do complexo amarelo piazoselenol entre Se(IV) e 3,3'-diaminobenzidina (DAB) seguido por sua extração em 1-undecanol e a medida da absorção molecular em 434 nm. O Se inorgânico total foi determinado após a redução do Se(VI) a Se(IV). A concentração de Se(VI) é calculada pela diferença entre o Se total e Se(IV). Nas condições otimizadas, foram obtidos um fator de enriquecimento de 133 e um limite de detecção de 1,6µg L-1. O desvio padrão relativo foi de 2,1% para uma solução contendo 50,0µg L-1 (n = 6) e a curva analítica de calibração foi linear no intervalo de 5,0-600,0µg L-1 para a pré-concentração de 20,0 mL da amostra aquosa. O método foi aplicado com sucesso na determinação de Se em alho, em pastilhas de selênio e em amostras de água. A exatidão foi avaliada usando experimentos de adição-recuperação e uma amostra de água certificada.

In this study a simple and inexpensive dispersive liquid-liquid microextraction-solidified floating organic drop (DLLME-SFOD) has been reported for the separation and speciation of inorganic selenium prior to its spectrophotometric determination. The method is based on the formation of a yellow piazselenol complex between the Se(IV) and 3,3'-diaminobenzidine (DAB) followed by its extraction into 1-undecanol and the measurement of its absorption at 434 nm. Total inorganic selenium is determined after the reduction of Se(VI) to Se(IV). The concentration of Se(VI) is calculated by the difference between the total selenium and Se(IV). Under the optimized conditions, an enrichment factor of 133, a detection limit of 1.6µg L-1, a relative standard deviation of 2.1% at 50.0µg L-1 (n = 6) and a linear dynamic range of 5.0-600.0µg L-1 for the preconcentration of 20.0 mL of aqueous sample was obtained. The method was successfully applied to the determination of selenium in garlic, selenium plus tablet and water samples. The accuracy was evaluated through the recovery experiments and the analysis of a certified water sample.

A dispersive liquid-liquid microextraction based on solidification of floating organic drop for simultaneous extraction of trace amounts of nickel, cobalt and copper followed by their determination with electrothermal atomic absorption spectrometry was developed. 300 µL of acetone and 1-undecanol was injected into an aqueous sample containing diethyldithiocarbamate complexes of metal ions. For a sample volume of 10 mL, enrichment factors of 277, 270 and 300 and detection limits of 1.2, 1.1 and 1 ng L-1 for nickel, cobalt and copper were obtained, respectively. The method was applied to the extraction and determination of these metals in different water samples.

Um procedimento de extração no ponto nuvem (CPE) foi desenvolvido para a separação e pré-concentração de baixas concentrações de cobalto previamente à determinação por espectrometria de absorção atômica em chama (FAAS). O procedimento é baseado na formação do complexo de Co(II) com 2-[(2-mercaptofenilimino)metil]fenol (MPMP), seguido pela extração em fase rica em surfactante Triton X-114. Alguns parâmetros importantes que afetam a complexação e extração, tais como pH, concentrações do agente quelante e do surfactante, temperatura e tempo de equilíbrio, foram otimizados. Sob condições ótimas, a pré-concentração de um volume de 25 mL da amostra resultou em um limite de detecção de 0,21 µg L-1, um fator de enriquecimento de 97 e um desvio padrão relativo de 1,2% (n = 8, 60 µg L-1) para a determinação de Co(II) por FI-FAAS. O método foi aplicado com sucesso para amostras de água, vitamina B12 e ampolas de complexo B. A exatidão do método foi comprovada por experimentos de adição-recuperação, análise independente por espectrometria de absorção atômica com forno de grafite e determinação de Co em material de referência certificado.

A cloud point extraction (CPE) procedure was developed for the separation and preconcentration of trace amounts of cobalt prior to its determination by flame atomic absorption spectrometry (FAAS). The procedure is based on the formation of Co(II) complex with 2-[(2-mercaptophenylimino)methyl]phenol (MPMP) followed by its extraction into a Triton X-114 surfactant-rich phase. Some important parameters affecting both complexation and extraction, such as pH, concentrations of chelating agent and surfactant, temperature, and time of equilibration, were optimized. Under optimum conditions, the preconcentration of a volume of 25 mL of sample resulted in a limit of detection of 0.21 µg L-1, an enhancement factor of 97, and a relative standard deviation of 1.2 % (n = 8, 60 µg L-1) for the determination of Co(II) by FI-FAAS. This procedure was successfully applied to water, vitamin B12 and B-complex samples. The accuracy was assessed employing addition-recovery experiments, independent analysis by graphite furnace atomic absorption spectrometry and by using a certified reference material.

Um sistema de injeção em fluxo sensível e simples foi desenvolvido para separação, préconcentração e determinação de tálio. A pré-concentração é baseada na sorção do analito em uma microcoluna de dibenzo-18-coroa-6 (DB18C6) imobilizada em alumina revestida com surfactante e subseqüente eluição com solução de ácido nítrico (500 µL, 2 mol L-1). A concentração de tálio no eluente foi determinada por espectrometria de absorção atômica com atomização eletrotérmica. Os fatores que influenciaram a sorção e dessorção de íon tálio foram investigados. Para um volume da amostra de 5 mL, a calibração foi linear no intervalo de 0,1 a 20 µg L-1 (r = 0,9996) com um limite de detecção de 0,05 µg L-1. A capacidade máxima de sorção foi de 1432 µg de tálio por grama do sorbente. A precisão do método para 1 µg L-1 foi 5,7% RSD (n = 11). O método foi aplicado para determinação de tálio em água, cabelo, unha e em materiais de referência certificados. A exatidão foi avaliada empregando experimentos de adição e recuperação ou por comparação dos resultados com materiais de referência certificados.

A simple and sensitive flow injection system was developed for separation, preconcentration and determination of thallium. Preconcentration is based on the analyte sorption on a microcolumn of dibenzo-18-crown-6 (DB18C6) immobilized on surfactant coated alumina with subsequent elution using a nitric acid solution (500 µL, 2 mol L-1). The concentration of thallium in the eluent was determined using electrothermal atomic absorption spectrometry. Factors influencing the sorption and desorption of thallium ion were investigated. Using a sample volume of 5 mL, the calibration was linear from 0.1 to 20 µg L-1 range (r = 0.9996) with a detection limit of 0.05 µg L-1. The maximum sorption capacity was 1432 µg of thallium per gram of sorbent. The precision of the method at 1 µg L-1 was 5.7% RSD (n = 11). The method was applied for determination of thallium in water, hair, nail, and standard reference samples. The accuracy was assessed using addition-recovery experiment or by comparison of the results with certified reference materials.

O presente estudo examina a possibilidade de imobilização do ácido esteárico em naftaleno microcristalino para a preparação de microcoluna e avalia seu potencial para adsorção e pré-concentração de quantidades traço de íons metálicos. Esse sorvente apresentou alta afinidade para chumbo. Conseqüentemente, foi elaborada uma rápida estratégia de pré-concentração empregando sistema de injeção em fluxo para determinação de chumbo por Espectrometria de Absorção Atômica com chama. A pré-concentração foi baseada no acúmulo do analito na microcoluna de ácido esteárico imobilizado e subseqüente eluição por injeção de pequeno volume de solução de ácido nítrico 1 mol L-1 (250 µL). Um volume de amostra de 20 mL resultou em um fator de pré-concentração de 84 vezes e o desvio padrão relativo para soluções contendo 40 e 200 µg L-1 foi 5,1 e 1,2%, respectivamente. O procedimento foi aplicado para água de torneira, de rio e de mar, suco de maçã, folha de beterraba, urina e aço inoxidável certificado. A exatidão foi comprovada por experimentos de recuperação, por Espectrometria de Absorção Atômica com Forno de Grafite e análise de um material de referência certificado composto por aço inoxidável.

The present study examines the possibility of immobilization of stearic acid on microcrystalline naphthalene for preparation of microcolumn and evaluation of its potential for adsorption and preconcentration of trace amounts of metal ions. It was found that this sorbent has high affinity for lead. Consequently, a rapid on-line preconcentration technique for the determination of lead by Flow Injection Flame Atomic Absorption Spectrometry had been devised. Preconcentration was based on accumulation of analyte on immobilized stearic acid microcolumn and subsequent elution by injection of a small volume of nitric acid (250 µL of 1 mol L-1). A sample volume of 20 mL resulted in a preconcentration factor of 84, and relative standard deviations for solutions containing 40 and 200 µg L-1 were 5.1 and 1.2%, respectively. The procedure was applied to tap water, river water, sea water, apple juice, beet leaf, urine, and certified stainless steel. The accuracy was proved by performing recovery experiments, Graphite Furnace Atomic Absorption Spectrometry measurements, and analysis of a stainless steel certified reference material.