Ultra-trace monitoring of copper in environmental and biological samples by inductively coupled plasma atomic emission spectrometry after separation and preconcentration by using octadecyl silica membrane disks modified by a new schiff's base

Ultra-trace amounts of Cu(II) were separated and preconcentrated by solid phase extraction on octadecyl-bonded silica membrane disks modified with a new Schiff,s base (Bis- (2-Hydroxyacetophenone) -2,2-dimethyl-1,3-propanediimine) (SBTD) followed by elution and inductively coupled plasma atomic emission spectrometric detection. The method was applied as a separation and detection method for copper(II) in environmental and biological samples. Extraction efficiency and the influence of sample matrix, flow rate, pH, and type and minimum amount of stripping acid were investigated. The concentration factor and detection limit of the proposed method are 500 and 12.5 pg mL-1, respectively.

Solid phase extraction of zinc with octadecyl silica membrane disks modified by N,N'-disalicylidene-1,2-phenylendiamine and determination by flame atomic absorption spectrometry

A procedure for separation and preconcentration of trace amounts of Zn(II) from aqueous media is proposed. The procedure is based on the adsorption of Zn2+ on octadecyl bonded silica membrane disk modified with N,N'-disalicylidene-1,2-phenylendiamine at pH 7. The retained zinc ions were then stripped from the disk with a minimal amount of 1.5 mol L-1 hydrochloric acid solution as eluent, and determined by flame atomic absorption spectrometry. Maximum capacity of the membrane disk modified with 5 mg of the ligand was found to be 226 µg Zn2+. The relative standard deviation of zinc for ten replicate extraction of 10 µg zinc from 1000 mL samples was 1.2%. The limit of detection of the proposed method was 14 ng of Zn2+ per 1000 mL. The method was successfully applied to the determination of zinc in natural water samples and accuracy was examined by recovery experiments and independent analysis by graphite furnace atomic absorption spectrometry (GFAAS).

Construção de uma cela de fluxo para medidas por espectrofotometria em fase sólida

A simple and low cost flow cell is proposed for measurements by solid-phase spectrophotometry employing a conventional spectrophotometer. The flow cell geometry allows the employment of a large amount of the solid support without causing both excessive attenuation of the radiation beam and increasing of the back-pressure. The adaptation of the flow cell in the optical path of the spectrophotometer in order to increase the precision is discussed. The flow cell characteristics were demonstrated by measurements of Co(II), employing 1-(2-tiazolylazo)-2-naphthol (TAN) immobilized on C18 bonded silica as solid support. The apparent molar absorptivity and coefficient of variation were estimated as 1.86 x 10(5) L mol-1 cm-1 and 1.4 % (n=15). A sample throughput of 40 determinations per hour and a detection limit of 15 mug L-1 (99.7 % confidence level) were achieved.

Inhibition of the polymerase chain reaction by sputum samples from tuberculosis patients after processing using a silica-guanidiniumthiocyanate DNA isolation procedure

With the objective to evaluate PCR-mediated detection of Mycobacterium tuberculosis DNA as a diagnostic procedure for diagnosis of tuberculosis in individuals attending ambulatory services in Primary Health Units of the City Tuberculosis Program in Rio de Janeiro, Brazil, their sputum samples were collected and treated with a DNA extraction procedure using silica-guanidiniumthiocyanate. This procedure has been described to be highly efficient for extraction of different kind of nucleic acids from bacteria and clinical samples. Upon comparing PCR results with the number of acid-fast bacilli, no direct relation was observed between the number of bacilli present in the sample and PCR positivity. Part of the processed samples was therefore spiked with pure DNA of M. tuberculosis and inhibition of the PCR reaction was verified in 22 out of 36 (61%) of the samples, demonstrating that the extraction procedure as originally described should not be used for PCR analysis of sputum samples.

Connectivity in sol-gel silica glasses

In this work it is carried out a review on structural parameters related to the evaluation of pore connectivity of nanostructures. The work describes parameters and methods of evaluation of geometric parameters. The concepts of connectivity are applied to silica gels and glasses obtained from sol-gel process. The study of pores connectivity was carried out using a combination of geometric modeling and experimental evaluation of specific surface area and pore volume. The permeability of the pore structure is evaluated and a permeability geometric factor, Pg, is proposed.

O relevante papel do agente sililante na modificação de superfícies de polímeros

The applicability of the silylant agents of the general formula Y3Si-R-X, depends on the reactivity of Y group (halide or alcoxide) attached to silicon and the organic function X (halide, amine, thiol, cyanide, etc) in the extreme position of the chain. Both groups are linked together by an organic chain R, containing usually three methylene groups. A series of these agents can be covalently bonded to an inorganic matrix, since the available OH groups are distributed on the surface, making silica gel the most common support. However, other inorganic oxides, zeolites, lamellar inorganic phosphates and chrysotile can also have these agents anchored. Some illustration are presented for immobilized surface in the use as extractors of cations from dilute aqueous or non-aqueous solutions, catalysts agents, ionic exchanged materials, support for enzyme immobilization, chromatographic applications, use in some industrial features and in many other areas. The evolution of this exciting research field to produce new materials, for many tecnological applications, is strongly dependent on the development of a sensible systematic process for the synthesis of a series of new specific silylant agents.

Adsorção do complexo H[Ru(III)Cl2(H2EDTA)] sobre a superfície da sílica gel modificada com [3-(2-aminoetil) aminopropil]trimetoxissilano em soluções etanólicas

Silica gel was functionalized with [3-(2-aminoethyl)aminopropyl]trimethoxysilane group (SF-AEATS) and the characterization by chemical analysis (N) and infrared spectroscopy confirmed the functionalization. The capacity of the modified silica to adsorb the complex Ru(III)-EDTA from ethanolic solution was studied. The selectivity coefficients of the complex formed on the support obtained was (Gñ), 2,07 x 10(4) L/mol and the average number of ligand bonded by one metal ion on the support (ñ) was ~ 1.

Comportamento da atomização eletrotérmica de ouro, prata, bismuto, cádmio, chumbo e estanho em soluções aquosas e em etanol, a partir de diferentes superfícies atomizadoras

The atomization behavior of Au, Ag, Bi, Cd, Pb, and Sn from pyrolitic graphite coating (L'vov platform) with the use Pd and Mg solutions, and zirconium coated platform with the analytes in nitric acid 0.2% v/v and in ethanol was investigated. In ethanol medium, the sensitivity gain was three-fold for Bi and Cd using Zr as modifier. Without modifier, the ethanol medium is appropriate only for Au and Cd. In nitric acid medium, the Zr coated platform elevates sensitivity at least two-fold for Bi and Cd. The method was applied to the determination of Ag, Au and Bi of certified steel samples, after on-line preconcentration, sorption on a minicolumn filled with C-18 bonded to silica gel and elution with ethanol. The concentrations obtained agreed with the recommended values.

Aplicação e modificação química da sílica gel obtida de areia

The silica gel was obtained from sand and its surface was modified with POCl3 to produce Si-Cl bonds on the silica surface. Ethylenediamine was covalently bonded onto the chlorinated silica surface. The adsorption of the chlorides of divalent cobalt, nickel and copper was qualitatively studied to show that the bonding of ethylenediamine onto the silica gel surface produces a solid base capable of chelating metal ions from solution. The experiments illustrate the extraction of silica gel, its reactivity, the development of modified surfaces and its application in removing metal ions from water and are deigned for undergraduate inorganic chemistry laboratories.

A novel method for fast enrichment and monitoring of hexavalent and trivalent chromium at the ppt level with modified silica MCM-41 and its determination by inductively coupled plasma optical emission spectrometry

Chromium(III) at the ng L-1 level was extracted using partially silylated MCM-41 modified by a tetraazamacrocyclic compound (TAMC) and determined by inductively coupled plasma optical emision spectrometry (ICP OES). The extraction time and efficiency, pH and flow rate, type and minimum amount of stripping acid, and break- through volume were investigated. The method's enrichment factor and detection limit are 300 and 45.5 pg mL-1, respectively. The maximum capacity of the 10 mg of modified silylated MCM-41 was found to be 400.5±4.7 µg for Cr(III). The method was applied to the determination of Cr(III) and Cr(VI) in the wastewater of the chromium electroplating industry and in environmental and biological samples (black tea, hot and black pepper).

Obtaining high purity silica from rice hulls

Many routes for extracting silica from rice hulls are based on direct calcining. These methods, though, often produce silica contaminated with inorganic impurities. This work presents the study of a strategy for obtaining silica from rice hulls with a purity level adequate for applications in electronics. The technique is based on two leaching steps, using respectively aqua regia and Piranha solutions, which extract the organic matrix and inorganic impurities. The material was characterized by Fourier-transform infrared spectroscopy (FTIR), powder x-ray diffraction (XRD), x-ray fluorescence (XRF), scanning electron microscopy (SEM), particle size analysis by laser diffraction (LPSA) and thermal analysis.

Production of silica gel from residual rice husk ash

This paper presents a study on the production of silica gel in hydrothermal process using residual rice husk ash. Measurements of the chemical composition, X-ray diffraction, infrared spectroscopy, particle size distribution, and pozzolanic activity were carried out in order to characterize the obtained material, and the optimal silica gel was selected for use as a mineral additive in cement pastes. The compressive strengths were determined for cement pastes containing silica gel (0.0, 2.5 or 5% by mass) in different times. The results indicate that the mixtures containing silica gel showed improved mechanical behavior over all time periods evaluated.

Properties of silica from rice husk and rice husk ash and their utilization for zeolite y synthesis

This study compared properties of silica (SiO2) from rice husk (RH) and rice husk ash (RHA) extracted by acid- and heat-treatment. The SiO2 from RH was in amorphous phase with nearly 100% purity while that from RHA was in crystalline phase with 97.56% purity. Both extracted SiO2 were used in the synthesis of zeolite NaY but that from RH was better due to the efficiency in product recovery and simplicity of extraction. After the NaY was exchanged to NH4Y and calcined to convert to HY, the product did not carry over the textural properties of the parent NaY and NH4Y.

Use of new silica fillers as additives for polymers used in packaging of fruit

The objective of this work was to synthesize nanosilicas with different degree of hydrophobicity by the sol-gel method, using tetraethyl orthosilicate as a precursor. For this purpose, 3-aminopropyl triethoxysilane (APS) and 1,1,1,3,3,3 - hexamethyldisilazane (HMDS), were added during synthesis as modifiers. A commercial biopolymer (Hexamoll Dinch, BASF) intended for packaging of apples, was added to the new nanosilicas. The materials obtained were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, potentiometric titration, porosity, specific surface area and hydrophobicity/hydrophilicity by wetting test. Colorimetry was used to evaluate change in apple pulp color after contact with the different silicas.

Simultaneous preconcentration of Cu(II), Cd(II) and Mn(II) on silica-polyethylene glycol and determination by flame atomic absorption spectrometry

A simultaneous solid phase extraction procedure for enrichment of Cu(II), Cd(II) and Mn(II) has been developed. The method is based on adsorption of Cu(II), Cd(II) and Mn(II) ions on polyethylene glycol-silica gel pre-conditioned with acetate buffer (pH 5.5). The adsorbed metal ions are eluted with nitric acid (1 mol L -1) and determined by flame atomic absorption spectrometry. The calibration graph was linear in the range of 2-140 ng mL-1 for Cu(II), 1-40 ng mL-1 for Cd(II) and 4-100 ng mL-1 for Mn(II). The limits of detection were 0.66, 0.33 and 1.20 ng mL-1 for Cu(II), Cd(II) and Mn(II), respectively.