Selective Sorbent Enrichment of Nickel Ions from Aqueous Solutions using a Hierarchically Hybrid Organic-Inorganic Polymer Based on Double Imprinting Concept

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)This study involves the preparation of an ion imprinted organic-inorganic polymer (IIP) for selective sorbent enrichment of Ni(2+) from aqueous solutions with further determination by GF AAS. The hybrid polymeric network was prepared from a mixture of 2-aminoethyl-3-aminobutylmethyldimethoxysilane as functional monomer, and tetraethoxysilane as crosslinking agent, containing Ni(2+) and cetyltrimethylammonium bromide as templates. The polymers were characterized by IR, TG and SEM. The maximum adsorptive capacity of IIP towards Ni(2+) ions, determined by linear Langmuir model, was found to be 5.44 mg g(-1). When the selectivity coefficient of IIP was compared with the selectivity coefficient of NIP (non imprinted polymer) and IIP2 (ion imprinted polymer in the absence of surfactant), from the binary mixtures of Ni(2+)/Cu(2+), Ni(2+)/Co(2+), Ni(2+)/Cd(2+) and Ni(2+)/Zn(2+), values of relative selectivity coefficient (k') were 36.54 and 3.55, 1.22 and 2.03, 4.43 and 1.42, 28.60 and 1.74, respectively, demonstrating higher selectivity of IIP for Ni(2+) ions. The proposed method provided a limit of detection of 0.16 mu g L(-1) and was successfully applied for Ni(2+) determination in spiked water samples and in a phytoterapic product (Gingko Biloba) with satisfactory recovery values.213419430Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)INCT of Bioanalytical (Instituto Nacional de Ciencia e Tecnologia de Bioanalitica)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

EMPLOY OF SILICA GEL ORGANICALLY MODIFIED AND IONICALLY IMPRINTED FOR SELECTIVE ON-LINE PRECONCENTRATION OF COPPER IONS

EMPLOY OF SILICA GEL ORGANICALLY MODIFIED AND IONICALLY IMPRINTED FOR SELECTIVE ON-LINE PRECONCENTRATION OF COPPER IONS. The present work purposes the preparation of a silica gel sorbent organically modified with 2-aminoethyl-3-aminobutylmethyldimethoxysilane (AAMDMS) and imprinted with Cu(2+) ions by means surface imprinting technique and its use for selective on-line sorbent preconcentration of Cull ions with further UV-VIS spectrophotometric determination by flow injection analysis. The Cu(2+)-imprinted silica gel, when compared with non imprinted silica gel and silica gel, showed from the binary mixture Of Cu(2+)/Ni(2+) relative selectivity coefficient (k') of 6.84 and 5.43 and 6.64 and 19.83 for the mixture Cu(2+)/Pb(2+), thus demonstrating higher selectivity of Cu(2+)-imprinted silica gel towards Cull ions. Under optimized condition, the on-fine preconcentration method provided detection limit of 3.4 mu g L(-1) and linear range ranging from 30.0 up to 300.0 mu g L(-1) (r = 0.995). The accuracy of method was successfully assessed by analyzing different kind of spiked water samples with recovery values ranging from 92.2 up to 103.0%.33230130

Highly improved sensitivity of TS-FF-AAS for Cd(II) determination at ng L-1 levels using a simple flow injection minicolumn preconcentration system with multiwall carbon nanotubes

A new method for cadmium determination at ng L-1 levels is described. The method is based on the on-line coupling of a flow preconcentration system using multiwall carbon nanotubes (MWCNT) as sorbent with TS-FF-AAS determination. Cadmium preconcentration was at pH 4.9 onto an MWCNT minicolumn (30 mg) for 2 min at a 5.0 mL min(-1) flow rate. The elution step is performed by using 0.5 mol L-1 HNO3 and the cadmium desorbed is directly pumped to a TS-FF-AAS. All experimental parameters that play important roles in system performance were evaluated and optimized by means of fractional factorial designs and response surface methodology. The excellent characteristics of MWCNT as sorbent, mainly owing to its high surface area, make it possible to obtain a preconcentration factor of 51-fold, thus improving the detection and quanti. cation limits in TS-FF-AAS, 11.4 and 38.1 ng L-1, respectively. When the flow preconcentration system, FI-TS-FF-AAS, was compared with FAAS alone, an increase in the sensitivity of 640-fold was obtained. The calibration graph was linear with a correlation coefficent higher than 0.999 from 38.1 to 1250 ng L-1. Repeatability of the measurements (n = 10), assessed as relative standard deviation (RSD), was found to be 6.5 and 2.1% for cadmium concentrations of 100 and 1000 ng L-1, respectively. Important parameters to characterize the flow preconcentration system were also evaluated, the consumption index being 0.196 mL, the concentration efficiency 25.5 min(-1) and the sample throughput 20 samples per hour. In order to demonstrate the accuracy of the system, addition and recovery studies in water samples (mineral water, tap water and river water) and cigarette samples were carried out. Moreover, for the same purpose, cadmium was determined in certified biological materials (Bovine Liver and Rye Grass), giving an average result in close agreement with the certified value.21111305131

CLOUD POINT EXTRACTION/PRECONCENTRATION OF COPPER IONS EXPLOITING THE FORMATION OF COMPLEXES WITH DMIT [4,5-DIMERCAPTO-1,3-DITHYOL-2-THIONATE]

CLOUD POINT EXTRACTION/PRECONCENTRATION OF COPPER IONS EXPLOITING THE FORMATION OF COMPLEXES WITH DMIT [4,5-DIMERCAPTO-1,3-DITHYOL-2-THIONATE]. The present study proposes a method for cloud point preconcentration of copper ions at pH 2.0 based on complexes formed with [4,5-dimercapto-1,3-dithyol-2-thionate] and subsequent determination by flame atomic absorption spectrometry (FAAS). Under optimal analytical conditions, the method provided limits of detection of 0.84 and 0.45 mu g L-1, by preconcentrating 12.0 and 24.0 mL of sample, respectively. The method was applied for copper determination in water samples, synthetic saliva, guarana powder, tea samples and soft drinks and the accuracy was assessed by analyzing the certified reference materials Dogfish Liver (DOLT-4) and Lobster Hepatopancreas (TORT-2).3581600160

Chromium(III) biosorption onto spent grains residual from brewing industry : equilibrium, kinetics and column studies

The use of industrial wastes for wastewater treatment as a strategy to their re-use and valorisation may provide important advances toward sustainability. The present work gives new insights into heavy metal biosorption onto low-cost biosorbents, studying chromium(III) biosorption onto spent grains residual from a Portuguese brewing industry both in batch and expanded bed column systems. Experimental studies involved unmodified spent grains and spent grains treated with NaOH. Metal uptake followed a rapid initial step, well described by the pseudo-second-order kinetic model up to 27 h, indicating chemisorption to be the rate-limiting step. Beyond this period intraparticle diffusion assumed an important role in the uptake global kinetics. The best fit for equilibrium data was obtained using the Langmuir model, with unmodified spent grains having the higher maximum uptake capacity (q max = 16.7 mg g1). In open system studies, using expanded bed columns, the best performance was also achieved with unmodified spent grains: Breakthrough time (C/C i = 0.25) and total saturation time (C/C i = 0.99) occurred after 58 and 199 h of operation, corresponding to the accumulation of 390 mg of chromium(III), 43.3 % of the total amount entering the column. These results suggest that alkali treatment does not improve spent grains uptake performance. Changes in biomass composition determined by Fourier transform infrared spectroscopy suggested hydroxyl groups and proteins to have an important role in chromium(III) biosorption. This study points out that unmodified spent grains can be successfully used as low-cost biosorbent for trivalent chromium.The authors would like to thank the Portuguese brewing industry UNICER for all the support and FCT (Fundacao para a Ciencia e a Tecnologia) financial support through the Grant PRAXIS XXI/BD/15945/98

Molecularly-imprinted solid phase extraction of catechol from aqueous effluents for its selective determination by differential pulse voltammetry

A polymeric sorbent based on molecular imprinting technology has been synthesized and applied to selectively extract catechol from water samples with subsequent determination by differential pulse voltammetry (DPV). The non-covalent polymer was prepared by bulk polymerization using catechol and 4-vinylpyridine as template and monomer, respectively. The effect of the flow and chemical variables associated to the performance of the solid phase extraction procedure was investigated and optimized using a 2(5-1) fractional factorial design as well as Doehlert design. A study of selectivity was carried out percolating a standard aqueous solution, which contained a mixture of catechol and five phenolic compounds (4-chloro-2-methoxyphenol, 4-aminophenol, 2-cresol, 2-methoxyphenol and 4-chloro-2-metoxyphenol) through the polymer packed into a cartridge followed by the elution with methanol/acetic acid (4:1, v/v) solution. Differential pulse voltammograms obtained from the eluted solution indicated that all compounds were retained on the sorbent since an overlapped peak was verified, showing the necessity to include a washing step. For this task, methanol, tetrahydrofuran, acetonitrile, dichoromethane and chloroform were checked as washing solvent, in which chloroform was able to establish the specific interaction between catechol and those sites of molecularly-imprinted polymers (MIP). Recovery higher than 95% was obtained for extraction of catechol even in the presence of structurally similar phenolic compounds. The procedure was further applied for catechol determination in aqueous effluent from paper mill industry and river water. (c) 2005 Elsevier B.V. All rights reserved.54841671111

Biosorption of heavy metals using rice milling by-products. Characterisation and application for removal of metals from aqueous effluents

The morphological characteristics as well as chemical composition of rice husks were evaluated by different techniques such as spectroscopy and thermogravimetry. The material, which is considered a by-product obtained from rice milling, was then investigated as a potential decontaminant of toxic heavy metals present in laboratory effluents. Studies using glass columns were carried out at room temperature employing 100 ml of synthetic solutions containing Cd(II) and Pb(11) at 100 mg l(-1) in order to study the effects of pH, flow rate and particle size on Cd(H) and Pb(11) adsorption. After establishing the optimised conditions, the potentiality of rice husks for removing Cd(II) and Pb(II) ions from 100 ml of laboratory effluent, presenting concentrations before treatment of 22 and 12 mg l(-1), respectively, was evaluated. The ability to take up other metals species, such as Al(111), Cu(II) and Zn(II), present in this effluent was also studied. According to the data obtained, under the optimised conditions (pH = 4.0, flow rate of 8.0 ml min(-1) and less than or equal to355 mum rice husk particle size), 30 g of husks were necessary to attain the permissible limits for effluent release, as recommend by the EPA, for those species evolved in this work (Al, Cd, Cu, Pb and Zn). (C) 2003 Elsevier Ltd. All rights reserved.54798799

OnLine coupling of a flow injection system to TS-FF-AAS for preconcentration and determination of lead in water and vegetables

An online solid phase preconcentration system coupled to thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for Pb(II) ions determination is described. In the preconcentration system, Pb( II) ions complexed with ammonium O,O-diethyl-dithiophosphate (DDTP) in an acidic medium are preconcentrated as a neutral complex onto 20 mg of polyurethane foam (PUF) packed into a mini-column. The complex retained in the PUF is then released to TS-FF-AAS by using an 80% (v/v) ethanol solution. Chemical and flow variables associated with the preconcentration, such as the pH dependence of the Pb-DDTP complex, the DDTP concentration, and preconcentration and elution flow rates were optimized by the univariate method. The best sample pH value and DDTP concentration achieved are 2.0 and 0.5% (w/v), respectively, while the best preconcentration and elution flow rates are 2.4 and 1.0 mL min(-1), respectively. Under the optimized conditions, the present method, which is operated in volume mode ( only 2 mL), makes possible the determination of Pb( II) ions within a linear range from 5.2 to 300.0 mu g L-1 with a detection limit of 1.5 mu g L-1 and analytical frequency of 16 h(-1). The precision (n = 10) assessed as relative standard deviation (RSD) is, respectively, 7.3 and 4.8% for 6 and 200 mu g L-1 solutions of Pb(II). The preconcentration system provides an enrichment factor of 6.4 and consumption index of 310 mu L. Hence, the coupling of the preconcentration system to TS-FF-AAS is proven to be an efficient strategy to enhance TS-FF-AAS detectability. The applicability of the method was verified by analyses of spiked water samples as well as with certified and reference vegetable materials.3891427144

A sensitive method for cadmium determination using an on-line polyurethane foam preconcentration system and thermospray flame furnace atomic absorption spectrometry

A new sensitive and low cost method for cadmium determination at mug l(-1) levels that combines an on-line preconcentration system with the thermospray flame furnace atomic absorption spectrometry technique (TS-FF-AAS) is described in this work. Cadmium is preconcentrated from an acidic medium (pH 2.0) by forming a complex with ammonium O,O-diethyldithiophosphate (DDTP), which is then adsorbed onto polyurethane foam (PUF). The elution step is performed by using 80% (v/v) ethanol. The effects of the chemical and flow variables associated with the preconcentration were studied, such as the pH of formation of the Cd-DDTP complex, the DDTP concentration, the preconcentration and elution flow rate and the mass of adsorbent. The present method was operated in volume-mode (2 ml) and provided a linear range from 0.4 to 15.0 mug l(-1) with a sample throughput of 16 h(-1). The increase of power detection related to TS-FF-AAS by coupling the preconcentration system was confirmed by the enhancement of sensitivity (ca. 5 times), when compared to the value for TS-FF-AAS alone, thus achieving a low detection limit (0.12 mug l(-1)). The accuracy of the method was confirmed from analyses of spiked water samples and by the use of a reference technique (ETAAS). Certified biological materials were also used for the same purpose.20696196