Pedro Orival Luccas

Solid-phase extraction system for Pb (II) ions enrichment based on multiwall carbon nanotubes coupled on-line to flame atomic absorption spectrometry

The present paper proposes the application of multiwall carbon nanotubes (MWCNTs) as a solid sorbent for lead preconcentration using a flow system coupled to flame atomic absorption spectrometry. The method comprises the preconcentration of Pb (II) ions at a buffered solution (pH 4.7) onto 30mg of MWCNTs previously oxidized with concentrated HNO(3). The elution step is carried out with 1.0molL(-1) HNO(3). The effect of the experimental parameters, including sample pH, sampling flow rate, buffer and eluent concentrations were investigated by means of a 2(4) full factorial design, while for the final optimization a Doehlert design was employed. Under the best experimental conditions the preconcentration system provided detection and quantification limits of 2.6 and 8.6mugL(-1), respectively. A wide linear range varying from 8.6 up to 775mugL(-1) (r>0.999) and the respective precision (relative standard deviation) of 7.7 and 1.4% for the 15 and 200mugL(-1) levels were obtained. The characteristics obtained for the performance of the flow preconcentration system were a preconcentration factor of 44.2, preconcentration efficiency of 11min(-1), consumptive index of 0.45mL and sampling frequency estimated as 14h(-1). Preconcentration studies of Pb (II) ions in the presence of the majority foreign ions tested did not show interference, attesting the good performance of MWCNTs. The accuracy of the method was assessed from analysis of water samples (tap, mineral, physiological serum and synthetic seawater) and common medicinal herbs submitted to the acid decomposition (garlic and Ginkgo Biloba). The satisfactory recovery values obtained without using analyte addition method confirms the feasibility of this method for Pb (II) ions determination in different type of samples.

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 quantification 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 coefficient 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.

Atomization of Al in a tungsten coil electrothermal atomic absorption spectrophotometer

Electrothermal atomic absorption spectrophotometry of Al in a tungsten coil atomizer was evaluated and applied for its determination in hemodialysis fluid. The system was mounted on a Varian Spectra AA-40 spectrophotometer with continuum background correction and all measurements, in peak height absorbance, were done at 309.3 nm. The purge gas was a mixture of 90% Ar plus 10% H(2). Observation height, gas flow, drying, pyrolysis and atomization steps were optimized. The heating program was carried out by employing a heating cycle in four steps: dry, pyrolysis, atomization and clean. The determination of Al in hemodialysis solutions was performed by using a matrix-matching procedure. Al in hemodialysis solutions was determined by TCA and by electrothermal atomization with a graphite tube atomizer. There is no differences between results obtained by both methods at a confidence level of 95%. The characteristic mass of Al by using the TCA was 39 pg and the detection limit was 2.0 mug l(-1).

Avaliacão de programas de aquecimento para espectrometria de absorção atômica com atomizacão eletrotérmica em filamento de tungstênio

A tungsten coil atomizer was used to investigate the effect of heating programs with constant or variable drying temperatures on the atomization of Al, Cd, Cr and Pb. The variation of the surface temperature in the tungsten coil furnace can occur during each heating step due to the design of the power supply, that may apply constant voltages during a programmed time. For volatile elements (Cd), losses in sensitivity were observed when the program with a variable temperature was used. On the other hand, these effects are negligible for less volatile elements (Al and Cr) and any tested program, in different acidic media, could be used without appreciable changes in sensitivities. The results allow the establishment of proper heating programs for elements with different thermochemical behavior in the tungsten coil atomizer.

Thermogravimetric investigations on the mechanism of decomposition of Pb compounds on a tungsten surface

Abstract Tungsten coils are used as electrothermal atomizers in atomic absorption spectrometry (ETA-W), but despite successful applications the atomization mechanism is still obscure. The use of the thermogravimetry (TG) can bring some information on decomposition pathways for atom formation, simulating the drying and pyrolysis steps employed in typical heating program cycles. Thermogravimetric curves of Pb salts with and without chemical modifiers, such as ascorbic, oxalic, tartaric acids, and glucose, or interferents (e.g. NaNO 3 ) were obtained using a lab-made tungsten sample holder in an 90% Ar plus 10% H 2 atmosphere usually employed in ETA-W. Intermediaries and residues of the pyrolysis step were characterized by X-ray diffraction. These data allows a better establishment of parameters for ETA-W and can help to find proper conditions to decrease interferences. It was showed that the general decomposition route is the formation of PbO by heating, oxide reduction by H 2 in the purge gas followed by volatilization of Pb.

A Homemade Autosampler/Injector Commutator for Flow Injection Analysis

An autosampler/injector commutator for flow injection analysis (FIA) was constructed with electronic components of used equipments. The apparatus is controlled by commercially available multifunctional interface (PCL711B) connected to a personal computer, and the software was written in Visual Basic language. The system was applied to water analysis and it presented satisfactory results. The low cost and simplicity are the principal characteristics of the autosampler/injector commutator.

Determination of Uranium in Environmental Water by Flow Injection Analysis using a Hybrid-Imprinted Polymer

A hybrid imprinted polymer was synthesized using 3-(trimethoxysilyl) propylmethacrylate 4 vinylpyridine as the inorganic monomer, metacrilic acid as the organic monomer, and the uranile ion as the template. The synthesis was performed via a sol-gel technique. The polymer was sieved and introduced into a minicolumn, which was coupled in a flow injection system with spectrophotometric detection to preconcentrate uranium and allow its determination at low concentration. The method had a linear dynamic range between 2.0–100 µg L−1, a detection limit of 0.40 µg L−1, a preconcentration factor of 97, a concentration efficiency of 19.4 min−1, a consumptive index of 0.227 mL, and a sampling frequency of 10 analyzes h−1. The imprinted polymer had an adsorptive capacity of 1.77 mg g−1. The method was employed for the determination of uranium in effluent and river water. The precision, expressed as the relative standard deviation, was lower than 5.5%. The accuracy was investigated by comparison with alpha spectrometry; the results were statistically the same. The speed of the process is an advantage compared to the traditional alpha spectrometry. In addition, the present method is green because of the low consumption of sample and reagents and is a useful alternative for uranium determination.

The Coffee Protective Effect on Catalase System in the Preneoplastic Induced Rat Liver

This study aimed to evaluate the effect of organic/conventional coffee in liver tissues in the cancer process, taking into account the level and activities of catalase. The experiments were carried out with 8 groups of rats during 12 weeks. They received two injections of ethylenediaminetetraacetic acid solution 1.5% (v/v) prepared in 0.9% NaCl or 1,2-dimethylhydrazine (DMH) subcutaneous dose of 40u2009mg·kg−1·bw−1 for 2 weeks. The organic/conventional coffee infusions were at 5, 10, and 20% and were incorporated to feed (100u2009mL of infusion·kg−1 of diet). The catalase activity showed a decrease for livers which received DMH and DMH plus organic coffee at 5% and 10%. However, an increase was observed for those receiving organic 20% and conventional 10% coffee, slowing down and favoring the reversibility of the carcinogenic process. By SDS-PAGE, we observed an intensity decrease of 59u2009kDa bands, as the percentage of coffee was increased. The iron concentration (by ET-AAS) confirmed the electrophoretic results, suggesting that the DMH influenced the catalase expression conditions, reducing the activity by the loss of iron ions. Thus, the coffee may restore the catalase system in the liver, exerting its chemopreventive effects.

CHAPTER 8:Some Aspects of Selenium Determination Employing Solid-Phase Extraction and Atomic Absorption Spectrometry

The selenium determination, as well as selenium speciation, continues to possess drawbacks to be overcome, mainly for complex samples. Inductively coupled plasma mass spectroscopy, which has very good sensitivity, presents limitations for speciation because it provides only total concentration of the selenium. On the other hand, chromatographic techniques also present good performances but, in generally, need a troublesome and slow sample preparation. Preconcentration techniques, such as solid-phase extraction, have been employed due to the low concentrations of selenium species. This text presents an overview about selenium determination, focusing mainly on solid-phase extraction and atomic absorption spectrometry.