Djane Santiago de Jesus

New Materials for Solid‐Phase Extraction of Trace Elements

Abstract The development of new sorbents and their application in preconcentration methods for determination of trace elements is a subject of great interest. This review summarizes and discusses several analytical methods involving the preparation and use of new solid‐phase materials. The performance and general properties of sorbents such as carbon nanotubes, imprinted ions, biosorbents, nanoparticles, and fullerene are discussed in detail. The perspective and future trends in the use of these materials are also considered.

Determination of Copper, Iron, Nickel, and Zinc in Ethanol Fuel by Flame Atomic Absorption Spectrometry Using On‐Line Preconcentration System

Abstract In this work, an on‐line system for preconcentration and determination of copper, iron, nickel, and zinc at µg L−1 level by flame atomic absorption spectrometry (FAAS) has been developed. Amberlite XAD‐4 functionalized with 3,4‐dihydroxybenzoic acid packed in a minicolumn was used as metal sorbent. The retained metals can be quickly eluted from sorbent material, with the eluent stream consisting of hydrochloric acid solution, directly to the nebulizer burner system of the FAAS. Analytical parameters were evaluated and the results demonstrated that all studied metals can be determined, using borate buffer to adjust the sample pH at 8.0. The results showed that the proposed method is simple and rapid. The limits of detection were estimated as 2.3, 5.0, 7.8, and 0.1 µg L−1 for copper, iron, nickel, and zinc, respectively, using a preconcentration time of 60 s and a sample flow rate of 5.5 mL min−1. Enrichment factors of 22, 15, 12, and 54 and coefficients of variations of 3.5, 4.4, 4.4, and 3.2% were obtained in the determination of copper, iron, nickel, and zinc, respectively. The system presented an analytical throughput of 10 samples per hour and was successfully applied in the determination of metals in ethanol fuel.

Derivative spectrophotometric determination of nickel using Br-PADAP

A major problem with spectrophotometric methods for nickel is cobalt interference, because many of the reagents for nickel also react with cobalt. In this work, the interference of cobalt in the determination of nickel using 2-(5-bromo-2-pyridylaxo)-5-diethylaminophenol (Br-PADAP) was eliminated by the use of derivative spectrophotometry, using the zero-crossing method for evaluation of the derivative signal. Br-PADAP reacts with nickel(II) in the presence of Triton X-100 to form a red complex with absorption maxima at 530 and 562 nm. The reactions parameters and the conditions for the measurements of the first-derivative signal were studied and the results demonstrated that using the derivative technique, Br-PADAP can be used for nickel determination with a selectivity higher than that of ordinary spectrophotometry and with a limit of detection of 0.2 ng ml(-1). The pH should be in the range 5.0-6.0 using an acetate buffer. The determination of nickel in the presence of cobalt was performed with conventional and derivative procedures, and the results demonstrated that only the derivative method should be used and, of the methods used for evaluation of the derivative signal, the zero-crossing method is the best. The proposed procedure was used for nickel determination in steels standards. The results demonstrated that the procedure has satisfactory accuracy and precision. Cobalt interference can be also eliminated by using dual-wave-length spectroscopy.

Molybdenum determination in iron matrices by ICP-AES after separation and preconcentration using polyurethane foam

Abstract A procedure is proposed for the separation and determination of molybdenum in iron matrices by a batch process. It is based on the solid-phase extraction of the molybdenum(V) ion as thiocyanate complex on polyurethane (PU) foam. The extraction parameters were optimized. Using 0.20 mol L–1 hydrochloric acid, a thiocyanate concentration of 0.10 mol L–1, 100 mg of polyurethane foam and shaking time of 10 min, molybdenum (5–400 μg) can be separated and preconcentrated from large amounts of iron (10 mg). Desorption was carried out instantaneously by conc. nitric acid or acetone. Distribution coefficients, sorption capacity of the PU foam and coefficients of variation were also evaluated. The effect of some ions on the separation procedure was assessed. Iron(III) should be reduced to iron(II). The proposed procedure was used to determine molybdenum in standard iron matrices such as steel and pure iron. The achieved results did not show significant differences with certified values.

Quantitative separation of zinc traces from cadmium matrices by solid-phase extraction with polyurethane foam

Abstract A system for separation of zinc traces from large amounts of cadmium is proposed in this paper. It is based on the solid-phase extraction of the zinc in the form of thiocyanate complexes by the polyurethane foam. The following parameters were studied: effect of pH and of the thiocyanate concentration on the zinc extraction, shaking time required for quantitative extraction, amount of PU foam necessary for complete extraction, conditions for the separation of zinc from cadmium, influence of other cations and anions on the zinc sorption by PU foam, and required conditions for back extraction of zinc from the PU foam. The results show that zinc traces can be separated from large amounts of cadmium at pH 3.0±0.50, with the range of thiocyanate concentration from 0.15 to 0.20 mol l −1 , and the shaking time of 5 min. The back extraction of zinc can be done by shaking it with water for 10 min. Calcium, barium, strontium, magnesium, aluminum, nickel and iron(II) are efficiently separated. Iron(III), copper(II) and cobalt(II) are extracted simultaneously with zinc, but the iron reduction with ascorbic acid and the use of citrate to mask copper(II) and cobalt(II) increase the selectivity of the zinc extraction. The anions nitrate, chloride, sulfate, acetate, thiosulphate, tartarate, oxalate, fluoride, citrate, and carbonate do not affect the zinc extraction. Phosphate and EDTA must be absent. The method proposed was applied to determine zinc in cadmium salts using 4-(2-pyridylazo)-resorcinol (PAR) as a spectrophotometric reagent. The result achieved did not show significant difference in the accuracy and precision (95% confidence level) with those obtained by ICP–AES analysis.

A separation method to overcome the interference of aluminium on zinc determination by inductively coupled plasma atomic emission spectroscopy

Abstract The use of polyurethane foam (PUF) to separate zinc from large amounts of aluminium and its determination by inductively coupled plasma atomic emission spectroscopy technique (ICP-AES) in aluminium matrices is described. The proposed method is based on the solid-phase extraction of the zinc(II) cation as a thiocyanate complex. Parameters such as effect of pH on zinc sorption, zinc desorption from the foam and analytical features of the procedure were studied. Results showed that the zinc(II) cation within the range from 0.02 to 65.0 μg in 0.2 mol l −1 thiocyanate solution and pH range from 1.0 to 4.0, could be quantitatively extracted by 0.1 g of PUF. The precision of the method was calculated as the relative standard deviation from a series of seven measurements. It was 3.9% for 1.0 μg of zinc in a volume solution of 50 ml. The proposed procedure was used for zinc determination in both aluminium alloys and salts with zinc concentration in the range from 50 to 300 μg g −1 . A standard addition technique was used and achieved results showing that this procedure has good accuracy and precision.

Preconcentration and Determination of Copper and Zinc in Natural Water Samples by ICP-AES After Complexation and Sorption on Amberlite XAD-2

O presente trabalho descreve um procedimento para separacao, preconcentracao e determinacao sequencial de quantidades traco de cobre e zinco em amostras de agua natural, por espectrometria de emissao atomica com plasma indutivamente acoplado (ICP-AES). Este metodo e baseado na complexacao dos ions cobre(II) e zinco(II) pelo 1-(2-thiazolylazo)-2-naphthol (TAN) e sorcao sobre a resina Amberlite XAD-2. Parametros tais como: quantidade de TAN, efeito de pH sobre a complexacao e sorcao dos complexos, tempo de agitacao para completa sorcao, concentracao dos ions metalicos, massa de resina Amberlite XAD-2 necessaria, dessorcao dos ions metalicos da resina XAD-2 e volume da amostra foram estudados. Os resultados demonstraram que os ions cobre(II) e zinco(II), na faixa de 0,10 a 100,00 mg, contidos em volume de solucao amostra de 400 mL, na faixa de pH de 5,7 a 8,3, sob a forma de complexos do TAN, e quantitativamente retido sobre a resina XAD-2. O tempo de agitacao requerido para sorcao e de 1 hora usando uma massa de resina de 1,4 g. A solucao para determinacao de cobre e zinco por ICP-AES e obtida, apos a dessorcao dos ions da resina, usando 5 mL de acido cloridrico 2 mol L-1, agitando o sistema por 5 min. O procedimento foi aplicado na determinacao de cobre e zinco em varias amostras de agua natural. A tecnica da adicao padrao foi aplicada e as recuperacoes obtidas revelaram que o procedimento proposto tem uma boa exatidao e precisao. Um alto fator de enriquecimento (80) e a simplicidade sao as principais vantagens neste procedimento.