A novel nanocomposite based on magnetic multiwalled carbon nanotubes coated with SiO2 and functionalized with 3-mercaptopropyltrimethoxysilane (3-MPTMS) was prepared for the efficient extraction and quantification of lead ions from water samples. The adsorption capacity of this adsorbent could reach 1.995 mg g-1 Pb2+ in an equilibrium time of 30 min. Under optimized conditions derived using the 25-1 fractional factorial design, a 45 mL aliquot of the sample was preconcentrated onto 90 mg of nanocomposite during 4 min. The lead ions adsorbed on the nanocomposite were eluted using 2 mol L-1 HNO3. The proposed method provided a preconcentration factor of 15.25 times, yielding limits of detection (LOD) and quantification (LOQ) of 0.56 and 1.86 µg L-1, respectively, and a linear range between 1.86 and 100.00 µg L-1. The relative standard deviations (RSD, n = 10), determined using solutions of Pb2+ at 10 and 120 µg L-1, were 2.3 and 2.1%, respectively. A high tolerance toward potentially foreign ions was observed. The proposed method was successfully applied to the rapid extraction of Pb2+ ions from different water samples, confirming good recovery values (90.33-109.53%); the accuracy of the method was evaluated through graphite furnace atomic absorption spectrometry (GF AAS) as a reference technique.

Ternary oxide silica-alumina-zirconia (SiO2/Al2O3/ZrO2) obtained by the sol-gel process was applied as novel adsorbent of ions in aqueous solution. Batch isotherms were performed using standard CuII, CdII and CaII solutions at variable pH and different concentrations. Adsorption capacity was best at weakly acidic pH. The maximum adsorption capacities were 2.28 mg g−1 for CaII, 9.89 mg g−1 for CdII, and 14.88 mg g−1 for CuII. The adsorption data fitted well to the single and dual-site Langmuir-Freundlich isotherm models. However, since the adsorption is very low in the sites with high energy, the single-site Langmuir-Freundlich provided a good fit as well. Whereas, the site responsible for the most ion adsorption was assigned to the Zr−OH group. A real sample of produced water was also tested. The new adsorbent showed a wide ability to retain many metal ions (alkali-earth, transition, and p-block metals) and even some anions were also caught by the adsorbent. The ternary oxide silica-alumina-zirconia was found to be a promising alternative adsorbent for metal ions in aqueous media.

This work deals on the preparation of silicon oxycarbide (SiOC) and silicon boron oxycarbide (SiBOC) ceramics from pyrolysis involving alkoxysilanes with different organic groups. Boron content, organic substituent and annealing time were evaluated on crystallization and composition of resulting ceramics. B-free precursors composed of methyltriethoxysilane (MTES), phenyltriethoxysilane (PTES) and vinyltrimethoxysilane (VTMS) were obtained by the sol-gel method, whilst B-containing precursors were prepared by adding to each alkoxysilane a proper amount of boric acid resulting in B/Si atomic ratios of 0.1 and 0.5. Precursors were pyrolyzed at 1500 ºC for 1 and 3 h to produce respective SiOC and SiBOC ceramics. X-ray diffraction (XRD) patterns revealed enhanced SiC phase crystallization for PTES-derived ceramics, followed by those containing vinyl and methyl groups, which was also confirmed by X-ray photoelectron spectroscopy (XPS) from percentages of SiºC and Si?O bonds. Csp2 and Csp3 amounts varied among ceramics, indicating direct influence of organic substituent on conductive carbon phase development. Boron addition induced the growth of SiC crystallites, having more evident effect in matrices with higher proportions of amorphous fraction and lower residual carbon amounts. Organic group nature, boron content and annealing time played an important role for production and evolution of SiC and C phases into ceramics.

This review focuses on the use of functionalized carbon nanotubes (CNTs) on the development of preconcentration methods with substantial contributions on selectivity and sensitivity for metal ions determination. CNTs have been usually employed in the development of preconcentration/speciation coupled to spectroanalytical techniques for ions determination at trace levels in different kind of samples. With regard the electroanalytical ones, this material has been widely used in adsorptive voltammetry procedures. Despite intrinsic features of CNTs, they suffer from poor dispersion in aqueous medium and wettability, thus making them very useful for sorption of hydrophobic metallic complex, but few indicated for metallic ions. Thus, different syntheses strategies, purification and chemical and physical approaches for surface functionalization/modification have been reported for improving the applicability of CNTs for a wide range of analytes. Therefore, apart from the brief description of the main physical and chemical characteristics of the carbon nanotubes, this review report the critical evaluation of main applications of modified CNTs as solid phase and as electrodic material for metal ions determination in environmental samples, food and biological using spectroanalytical techniques such as flame and graphite furnace atomic absorption spectrometry and inductively coupled plasma atomic emission spectrometry and electroanalytical mainly the adsorptive voltammetric ones.

A flow-injection preconcentration system using detection by the thermospray flame furnace atomic absorption spectrometry (FIA-TS-FF-AAS) is proposed. Cd2+ are adsorbed on avocado seed activated carbon (ASAC) packed into a cylindrical mini-column and eluted using HCl solutions for the detection system. A 25–1 fractional factorial and Doehlert matrix design were employed to determine the optimum conditions for cadmium preconcentration (pH 7.68, buffer concentration (Tris/Tris-HCl) of 0.023 mol L-1, eluent concentration (HCl) of 2.0 mol L-1, the adsorbent mass of 100.0 mg and preconcentration flow rate of 4.8 mL min-1). The preconcentration method presents linearity within the range of 0.41-15.00 µg L-1, limits of quantification and detection of 0.41 and 0.12 µg L-1, respectively, preconcentration factor of 10.7, consumption of index of 0.93 mL and sample throughput of 26 h-1. The precision assessed as the relative standard deviation (RSD) were found to be 0.48, 0.90 and 2.30% for inter-day precision (n = 2), and 0.30, 0.44 and 2.48% for intra-day precision (n = 6) for respective cadmium concentration of 0.50, 5.00 and 15.00 µg L-1. The proposed method was applied satisfactorily in samples of cigarette (62.84 ± 11.28 µg kg-1), human hair (69.61 ± 2.38 µg kg-1) and water samples [lake (0.65 ± 0.01 µg L-1), tap and mineral].

A new online solid phase preconcentration method using the new SiO2/Al2O3/SnO2 ternary oxide (designated as SiAlSn) as chelating agent free-solid phase extractor (CAF-SPE) coupled to flame atomic absorption spectrometry (FAAS) for Pb2+ determination at trace levels in different kind of samples is proposed. The solid adsorbent has been characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron miscroscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray fluorescence spectroscopy (XRF) and textural data. The method involves the preconcentration using time-based sampling of Pb2+ solution at pH 4.3 through 100.0 mg of packed adsorbed into a mini-column under flow rate of 4.0 mL min-1 during 5 min. The elution step was accomplished by using 1.0 mol L-1 HCl. A wide range of analytical curve (5.0-400.0 µg L-1), high enrichment factor (40.5), low consumption index (0.5 mL) and low limits of quantification and detection, 5.0 and 1.5 µg L-1, respectively, were obtained with the developed method. Practical application of method was tested on water samples, chocolate powder, Ginkgo biloba and sediment (certified reference material). On the basis of the results, the SiAlSn can be considered an effective adsorbent belonging to the class of CAF-SPE for Pb2+ determination from different matrices.

Carbon black (CB) grafted with 3-mercaptopropyltrimethoxysilane (3-MPTMS) was used as solid phase extractor for Cd2+ in a flow injection system coupled to flame atomic absorption spectrometry (FAAS). The influence of pH, buffer concentration, preconcentration flow rate and eluent concentration on preconcentration of Cd2+ were investigated by means of chemometric tools. The characterization of the adsorbent chemically modified was performed by Fourier transform infrared, scanning electron microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis, Raman spectroscopy and textural analysis. To perform the on-line preconcentration, 20.0 mL of a pH 7.0 Cd2+ solution at a flow rate of 4.0 mL min−1 was loaded through 30.0 mg of modified CB and then eluted with 1.0 mol L−1 HCl toward the FAAS instrument. The limits of detection and quantification were found to be 0.20 and 0.66 µg L−1, respectively. Addition and recovery tests carried out in real samples (mineral, tap and saline waters, and cigarette sample) and the analysis of certified reference material (TORT-2, lobster hepatopancreas reference) attested the applicability of proposed method.

It is well known that selectivity of molecularly imprinted polymers (MIPs) depends on adequate choice of functional monomer before the experimental synthesis. Computational simulation seems to be an ideal way to produce selective MIPs. In this work, we have proposed the use of semi-empirical simulation to obtain the best monomer able to strongly interact with ciprofloxacin. Twenty functional monomers were evaluated through semi-empirical quantum chemistry method and three MIPs were synthesized using the monomers acrylamide (M5), acrylic acid (M4) and 1-vinylimidazole (M16), yielding the maximum adsorption capacities of 282.0, 223.8 and 202.5 μmol g−1, respectively, as predicted by the computational simulation. From competitive adsorption studies in the presence of structurally similar compounds, the MIP synthesized with acrylamide was found to possess higher specific selectivity factors (S) if compared to non-imprinted polymer (NIP), thus indicating good recognition selectivity for the ciprofloxacin.

No presente estudo, um novo material compósito (SiO2/TiO2/ZnO) foi avaliado para pré-concentração de cobre em amostras de água e alimentos. O sorvente foi caracterizado por microscopia eletrônica de varredura (SEM), infravermelho com transformada de Fourier (FT-IR), análise de dados texturais, fluorescência de raios X por energia dispersiva (EDXRF) e difratometria de raios X (XRD). A pré-concentração em linha e determinação espectrofotométrica na região visível foi baseada na pré-concentração de 20,0 mL de amostra em pH 7,0 através de 50 mg do sorvente, numa vazão de 6,4 mL min-1. Um volume fixo de 0,3 mL de HNO3 0,5 mol L-1 elui os íons cobre que reagem com dietilditiocarbamato (DDTC) 0,3% (m/m) cujo complexo formado (Cu(DDTC)2) é monitorado a 452 nm. A seletividade do sorvente foi examinada avaliando o efeito de íons interferentes. O método proposto forneceu linearidade variando de 20,0 a 230,0 mg L-1 (r = 0,998), fator de pré-concentração de 35,9 e limite de detecção de 5,6 mg L-1. Amostras de água e alimentos foram analisadas com sucesso pelo método proposto e a exatidão foi checada por meio de análises de materiais certificados de referência de proteína e fígado de peixe.

In the present study, a new composite material (SiO2/TiO2/ZnO) for copper preconcentration in water and food samples was evaluated. The sorbent was characterized by scanning electronic microscopy (SEM), Fourier transform infrared spectrophotometry (FT-IR), textural data analyses, energy dispersive X-ray fluorescence (EDXRF) and X-ray diffractometry (XRD). The on-line preconcentration and visible spectrophotometric determination was based on loading 20.0 mL of sample at pH 7.0 through 50 mg of sorbent at a flow rate of 6.4 mL min-1. A fixed volume of 0.3 mL of 0.5 mol L-1 HNO3 elutes copper ions, in which react with 0.3% (m/m) diethyldithiocarbamate (DDTC) whose complex formed (Cu(DDTC)2) is monitored at 452 nm. The selectivity of sorbent has been examined by assessing the effect of interfering ions. The proposed method provided linearity ranging from 20.0 to 230.0 mg L-1 (r = 0.998), preconcentration factor of 35.9 and limit of detection of 5.6 mg L-1. Water and food samples were successfully analyzed by proposed method and the accuracy was checked by analysis of certified reference materials of protein and liver of fish.

In this paper, we describe the synthesis of an ion imprinted polymer (IIP) by homogeneous polymerization and its use in solid-phase to extract and preconcentrate zinc ions. Under optimal conditions (pH 5.0, preconcentration flow rate of 12.0 mL min-1, and eluted with 1.0 mol L-1 HNO3) this procedure allows the determination of zinc with an enrichment factor of 10.2, and with limits of detection and quantification of 1.5 and 5.0 µg L-1, respectively. The accuracy of our results was confirmed by analysis of tap water and certified reference materials: NIST 1570a (Spinach leaves) and NIST 1515 (Apple leaves).

Objetivou-se, neste trabalho, analisar a eficiência de resíduos de macadâmia (mesocarpo e endocarpo) com e sem modificações químicas na biossorção de íons cobre II. As modificações químicas no biossorvente foram realizadas com hidróxido de sódio (NaOH) e com NaOH mais ácido cítrico e comprovadas por espectroscopia na região do infravermelho, pela presença dos picos em 1710 e 1420 cm-1 como também pela microscopia eletrônica de varredura (MEV) observando-se aumento da rugosidade na superfície. Os melhores resultados de biossorção foram para o mesocarpo modificado com NaOH, em pH igual a 5. O tempo de equilíbrio adsorvente-adsorbato foi de 140 min; além disto, o sistema seguiu um modelo cinético de pseudo-segunda ordem e a capacidade máxima de biossorção foi de 28,82 mg g-1. As isotermas para os resíduos modificados com NaOH seguiram o modelo de Langmuir e as modificadas com ácido se ajustaram ao modelo de Freundlich. Constatou-se que o processo de biossorção foi espontâneo energeticamente devido aos valores negativos para a energia de Gibbs. Comprovou-se, então, que o adsorvente possui alta capacidade de dessorção; assim, este material poderá ser novamente reutilizado; portanto, este resíduo poderá, futuramente equipar, filtros para remoção de Cu2+.

The objective was to analyze the efficiency of macadamia waste with and without chemical changes in biosorption of copper II (Cu2+). The chemical changes in the biosorbent with sodium hydroxide (NaOH) and with NaOH and citric acid were evidenced by infrared spectroscopy by the appearance of peaks in 1710 and 1420 cm-1 and by scanning electron microscopy, observed an increase of roughness on the surface. The best results of the adsorption were observed in mesocarp modified with NaOH, in pH equal to 5. An equilibrium time adsorbent - adsorbate was 140 min, in addition, the system followed a kinetic model of pseudo-second order and the maximum adsorption capacity was 28.82 mg g-1. The isotherms for the residues modified with NaOH followed the Langmuir model and the modified with acid were adjusted to the Freundlich model. It was found that the adsorption process was energetically spontaneous due to negative values for the Gibbs energy and the adsorbent has a high capacity of desorption, so this material can be reused. Therefore, this residue is an excellent material to equip future filters for removal of copper II.

No presente trabalho um polímero com impressão molecular (MIP) seletivo para 4-aminofenol (4-APh) foi sintetizado através de técnica de polimerização em bulk. A polimerização foi realizada em tubo de vidro contendo 4-APh, Fe(III)protoporfrina(IX) (hemina, Fe(III)PPIX), ácido metacrílico (MAA), etileno glicol dimetacrilato (EGDMA) e 2,2'-azo-bis-iso-butironitrila (AIBN). O bloco de polímero foi moído e peneirado (106 µm) e o 4-APh foi removido das partículas do polímero pela extração com solução de metanol/ácido acético (4:1, v/v), deixando uma cavidade nas partículas do polímero. A hemina foi usada como um material sintético para imitar o centro ativo da peroxidase, criando um polímero com impressão molecular cataliticamente ativo. Os polímeros foram caracterizados por espectroscopia no infravermelho, análises termogravimétricas, microscopia eletrônica de varredura e análise do tamanho das partículas. O desempenho enzimático do polímero impresso foi avaliado baseado em parâmetros cinéticos incluindo Vmax e constante de Michaelis-Menten obtidas pelo gráfico de Lineweaver-Burk.

In the present work a selective molecularly imprinted polymer (MIP) for 4-aminophenol (4-APh) was synthesized by the bulk polymerization technique. Polymerization was carried out in a glass tube containing 4-APh, Fe(III)protoporphyrin(IX) (hemin, Fe(III)PPIX), methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA) and 2,2′-azo-bis-iso-butyronitrile (AIBN). The polymer block was ground and sieved (106 µm) and the 4-APh was removed from the polymer particles by leaching with a methanol/acetic acid (4:1, v/v) solution, which leaves a cavity in the polymer particles. Hemin was used as a synthetic material to mimic the active center of peroxidase creating a catalytically active molecularly imprinted polymer. The polymers were characterized by infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and particle size analysis. The enzymatic performance of the imprinted polymer was evaluated based on kinetic parameters including Vmax and the Michaelis-Menten constant obtained from Lineweaver-Burk plots.

O presente trabalho descreve uma metodologia analítica para determinação simultânea de ácido ascórbico (AA) e ácido úrico (AU) por voltametria de pulso diferencial empregando o surfactante catiônico cloreto de cetilpiridínio. Medidas voltamétricas de pulso diferencial realizadas em pH 7,0 revelaram que o meio micelar catiônico permite separar em 282 mV os picos de oxidação de AA e AU na mesma solução, valor suficiente para determinar ambas as espécies simultaneamente. Como em pH 7,0 o AA está mais ionizado que o AU, sua atração eletrostática em direção às micelas catiônicas, formadas sobre a superfície do eletrodo de carbono vítreo, é maior; desta forma, promove a diminuição no sobrepotencial e o aumento na taxa de transferência de elétrons. Foram construídas curvas de calibração para AA e AU na faixa de concentração de 4,70 até 220 µmol L-1 e 0,50 até 110 µmol L-1. A metodologia proposta foi aplicada para a determinação de AA e AU em amostras de urina humana.

The present work describes an analytical methodology for simultaneous determination of ascorbic acid (AA) and uric acid (UA) by differential pulse voltammetry employing the cationic surfactant, cetylpyridinium chloride. Differential pulse voltammetry measurements revealed that the cationic micellar media may separate the oxidation peak potentials of AA and UA present in the same solution by about 282 mV, which is enough to determine both species simultaneously. As in pH 7.0 the AA is more ionized than UA, its electrostatic attraction towards the cationic micelles formed onto the surface of glassy carbon electrode is higher, therefore, promoting a decrease in the overpotential and increasing the electron transfer rate. Calibration curves to AA and UA in the concentration range from 4.70 up to 220 µmol L-1 and 0.50 up to 110 µmol L-1 were built. The proposed methodology was applied for the simultaneous determination of AA and UA in human urine samples.