Flow analysis by using solenoid valves for As(III) determination in natural waters by an on-line separation and pre-concentration system coupled to a tungsten coil atomizer

A flow system coupled to a tungsten coil atomizer in an atomic absorption spectrometer (TCA-AAS) was developed for As(III) determination in waters, by extraction with sodium diethyldithiocarbamate (NaDDTC) as complexing agent, and by sorption of the As(III)-DDTC complex in a micro-column filled with 5 mg C18 reversed phase (10 µL dry sorbent), followed by elution with ethanol. A complete pre-concentration/elution cycle took 208 s, with 30 s sample load time (1.7 mL) and 4 s elution time (71 µL). The interface and software for the synchronous control of two peristaltic pumps (RUN/ STOP), an autosampler arm, seven solenoid valves, one injection valve, the electrothermal atomizer and the spectrometer Read function were constructed. The system was characterized and validated by analytical recovery studies performed both in synthetic solutions and in natural waters. Using a 30 s pre-concentration period, the working curve was linear between 0.25 and 6.0 µg L-1 (r = 0.9976), the retention efficiency was 94±1% (6.0 µg L-1), and the pre-concentration coefficient was 28.9. The characteristic mass was 58 pg, the mean repeatability (expressed as the variation coefficient) was 3.4% (n=5), the detection limit was 0.058 µg L-1 (4.1 pg in 71 µL of eluate injected into the coil), and the mean analytical recovery in natural waters was 92.6 ± 9.5 % (n=15). The procedure is simple, economic, less prone to sample loss and contamination and the useful lifetime of the micro-column was between 200-300 pre-concentration cycles.

Rugged, Portable Tungsten Coil Atomic Emission Spectrometer

Tungsten coil atomic emission spectrometry is an ideal technique for field applications because of its simplicity, low cost, low power requirement, and independence from cooling systems. A new, portable, compact design is reported here. The tungsten coil is extracted from an inexpensive 24 V, 250 W commercial light bulb. The coil is housed in a small, aluminum cell. The emission signal exits from a small aperture in the cell, while the bulk of the blackbody emission from the tungsten coil is blocked. The resulting spectra exhibit extremely low background signals. The atomization cell, a single lens, and a hand-held charge coupled device (CCD) spectrometer are fixed on a 1 x 6 x 30 cm ceramic base. The resulting system is robust and easily transported. A programmable, miniature 400 W solid-state constant current power supply controls the temperature of the coil. Fifteen elements are determined with the system (Ba, Cs, Li, Rb, Cr, Sr, Eu, Yb, Mn, Fe, Cu, Mg, V, Al, and Ga). The precision ranges from 4.3% to 8.4% relative standard deviation for repetitive measurements of the same solution. Detection limits are in the 0.04 to 1500 mu g/L range. Accuracy is tested using standard reference materials for polluted water, peach leaves, and tomato leaves. For those elements present above the detection limit, recoveries range from 72% to 147%.

Direct determination of chromium in empty medicine capsules by tungsten coil atomic emission spectrometry

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Tungsten coil atomic emission spectrometry combined with dispersive liquid–liquid microextraction: A synergistic association for chromium determination in water samples

A novel and environment friendly analytical method is reported for total chromium determination and chromium speciation in water samples, whereby tungsten coil atomic emission spectrometry (WCAES) is combined with in situ ionic liquid formation dispersive liquid–liquid microextraction (in situ IL-DLLME). A two stage multivariate optimization approach has been developed employing a Plackett–Burman design for screening and selection of the significant factor involved in the in situ IL-DLLME procedure, which was later optimized by means of a circumscribed central composite design. The optimum conditions were complexant concentration: 0.5% (or 0.1%); complexant type: DDTC; IL anion: View the MathML sourcePF6−; [Hmim][Cl] IL amount: 60 mg; ionic strength: 0% NaCl; pH: 5 (or 2); centrifugation time: 10 min; and centrifugation speed: 1000 rpm. Under the optimized experimental conditions the method was evaluated and proper linearity was obtained with a correlation coefficient of 0.991 (5 calibration standards). Limits of detection and quantification for both chromium species were 3 and 10 µg L−1, respectively. This is a 233-fold improvement when compared with chromium determination by WCAES without using preconcentration. The repeatability of the proposed method was evaluated at two different spiking levels (10 and 50 µg L−1) obtaining coefficients of variation of 11.4% and 3.6% (n=3), respectively. A certified reference material (SRM-1643e NIST) was analyzed in order to determine the accuracy of the method for total chromium determination and 112.3% and 2.5 µg L−1 were the recovery (trueness) and standard deviation values, respectively. Tap, bottled mineral and natural mineral water samples were analyzed at 60 µg L−1 spiking level of total Cr content at two Cr(VI)/Cr(III) ratios, and relative recovery values ranged between 88% and 112% showing that the matrix has a negligible effect. To our knowledge, this is the first time that combines in situ IL-DLLME and WCAES.

Interfase y software de control para operar en sincronismo un automuestreador y un atomizador electrotérmico por filamento de tungsteno en espectrofotometría de absorción atómica

The interface and software for synchronous control of an autosampler and an electrothermal tungsten coil atomizer in atomic absorption spectrophotometry were developed. The control of the power supply, the trigger of the Read function of the spectrophotometer and the automatic operation of the autosampler was performed by software written in "TurboBasic". The system was evaluated by comparison of the repeatability of peak-height absorbances obtained in the atomization of lead by consecutive 10-µl injections of solutions (prepared in 0.2% v/v HNO3) using autosampler and manual sample introduction, and also by long term operation.

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.

Espectrometria de absorção atômica com atomização eletrotérmica em filamento de tungstênio: uma re-visão crítica

In this review it is presented some aspects of electrothermal atomic absorption spectrometry with tungsten coil (ETAW-AAS) since its beginning until the present days as well as the perspectives for this technique. Some aspects concerning its development and theoretical concepts are discussed. The analytical figures of merit such as limit of detection (LD), characteristic mass (m0), relative standard deviation (RSD), accuracy and precision are evaluated, compared and discussed considering published works. It is also evaluated its advantages, applications, limitations and instrumental development. The use of diode laser as radiation source and its perspectives to ETAW are also discussed.

Construção de espectrômetro de emissão atômica com atomização eletrotérmica em filamento de tungstênio (WCAES)

It is here discussed the development of a low cost analytical instrument with capacity for metals determination using atomic emission measurements in an electrothermal atomization system with a tungsten coil atomizer. The main goal was to show a new frontier for using this atomizer and to demonstrate that the simple instrumental arrangement here proposed has potential for portability and for solving analytical tasks related to metals determination. Atomic emission of calcium was selected for the adjustment of instrumental parameters and to evaluate the main characteristics of the lab-built instrument. Cobalt was determined in medicines and one alloy to demonstrate its feasibility.

Fault current test of a bifilar Bi-2212 bulk coil

A bifilar Bi-2212 bulk coil with parallel shunt resistor was tested under fault current condition using a 3 MVA single-phase transformer in a 220 V-60 Hz line achieving fault current peak of 8 kA. The fault current tests are performed from steady state peak current of 200 A by applying controlled short circuits up to 8 kA varying the time period from one to six cycles. The test results show the function of the shunt resistor providing homogeneous quench behavior of the HTS coil besides its intrinsic stabilizing role. The limiting current ratio achieves a factor 4.2 during 5 cycles without any degradation.

Use of diamond-like carbon with tungsten (W-DLC) films as biocompatible material

Diamond-like carbon (DLC), also known as amorphous hydrogenated carbon (a-C:H), are a class of materials with excellent mechanical, tribological and biological properties. When the DLC films are enhanced with other elements, all of these properties can be changed within a certain range. In this work, reactive magnetron sputtering was used to deposit W-DLC (hydrogenated tungsten carbide) films on Ti6A14V (implant material). Many films were made using pure tungsten (99.99%) target and different plasmas processes, with different ratio among argon and methane. It was possible to change the films composition (from pure amorphous carbon to carbon enhanced with tungsten) according to ratio of argon and methane plasma. Between all films processed, the carbon films enhanced with tungsten showed good results in the ""in vitro"" cytotoxicity testing. Raman spectroscopy was used to analyze the chemical bonds kinds and the chemical bonds quantities. The Rutherford Back Scattering (RBS) was used to analyze the films compositions. The chemical inertness was analyzed by scanning voltametry. W-DLC thin films obtained in these processes have low roughness, high chemical resistance, good adhesion and show a high biocompatibility, when compared with common DLC thin films. Hence we have concluded that the tungsten concentrations in the DLC films make an important role to improve the properties of the DLC layers. (C) 2007 Elsevier B.V. All rights reserved.

NMR shim coil design utilising a rapid spherical harmonic calculation method

A rapid spherical harmonic calculation method is used for the design of Nuclear Magnetic Resonance shim coils. The aim is to design each shim such that it generates a field described purely by a single spherical harmonic. By applying simulated annealing techniques, coil arrangements are produced through the optimal positioning of current-carrying circular arc conductors of rectangular cross-section. This involves minimizing the undesirable harmonies in relation to a target harmonic. The design method is flexible enough to be applied for the production of coil arrangements that generate fields consisting significantly of either zonal or tesseral harmonics. Results are presented for several coil designs which generate tesseral harmonics of degree one.

A coiled-coil region of an insect immune suppressor protein is involved in binding and uptake by hemocytes

Polydnaviruses are associated with certain parasitoid wasps and are introduced into the body cavity of the host caterpillar during oviposition. Some of the viral genes are expressed in host tissues and corresponding proteins are secreted into the hemocoel causing suppression of the host immune system. The Cotesia rubecula polydnavirus gene product, CrV1, effectively inactivates hemocytes by mediating cytoskeleton break-down. A precondition for the CrV1 function is the incorporation of the extracellular protein by hemocytes. Here, we show that a coiled-coil domain containing a putative leucine zipper is required for CrV1 function, since removal of this domain abolishes binding and uptake of the CrV1 protein by hemocytes. (C) 2002 Elsevier Science Ltd. All rights reserved.

Synthesis, characterization, and catalytic properties of a mesostructured lamellar xerogel tungsten oxide phase

Cetyltrimethylammonium bromide (CTAB) and n-hexadecylamine (HDA) have been used as template in the synthesis of a mesolamellar xerogel tungsten oxide phase (WO(3)/CTAB/HDA). The catalytic properties of the resulting material were investigated in the oxidation of cis-cyclooctene, styrene, and cyclohexane, using hydrogen peroxide (H(2)O(2)), terc-butyl hydroperoxide (t-BOOH), or m-chlorperbenzoic acid (m-CPBA) as oxygen transfer agent. In general, the catalytic results were comparable to those obtained with related systems, thus suggesting the potential application of this material as catalyst for epoxidation reactions. (C) 2011 Elsevier B.V. All rights reserved.

Prognostic impact of adenomatous polyposis coil gene expression in osteosarcoma of the extremities

Purpose: To evaluate the impact of adjuvant chemotherapy on the outcome of osteosarcoma of the extremities, and to identify prognostic factors using the expression of adenomatous polyposis coli (APC), cadherin and beta-catenin Wnt-signalling markers. Methods: The clinical, demographic, anatomic and pathological factors including a detailed analysis of the immunohistochemical expression of cadherin, B-catenin and APC were retrospectively examined in 97 patients with osteosarcoma of the extremities (metastatic and non-metastatic at diagnosis), treated with surgery and/or chemotherapy from 1985 to 2000. Results: APC immunoreactivity showed a statistically significant association with age and serum alkaline phosphatase levels (p = 0.025 and p = 0.038). When survival was the end-point of multivariate analysis, race segregated patients with poor survival as did lack of cadherin expression. For overall survival, cadherin immunoreactivity and the interaction between APC expression and response to adjuvant chemotherapy were significant (p = 0.012 and p < 0.001). No significant clinical association was evident with immunohistochemical expression of cadherin, beta-catenin. Conclusion: Lack of expression of cadherin was a significant variable to overall and disease-free survival. Significantly, positive APC immunoreactivity and adjuvant chemotherapy were associated with a favourable treatment response. Studies using newer immunohistochemical markers within the Wnt-signalling pathway may guide the development of more appropriate therapeutic targets for future individualised treatment. (C) 2010 Elsevier Ltd. All rights reserved.

An inverse design of an open, head/neck RF coil for MRI

Radio-frequency (RF) coils are a necessary component of magnetic resonance imaging (MRI) systems. When used in transmit operation, they act to generate a homogeneous RF magnetic field within a volume of interest and when in receive operation, they act to receive the nuclear magnetic resonance signal from the RF-excited specimen. This paper outlines a procedure for the design of open RF coils using the time-harmonic inverse method. This method entails the calculation of an ideal current density on a multipaned planar surface that would generate a specified magnetic field within the volume of interest. Because of the averaging effect of the regularization technique in the matrix solution, the specified magnetic field is shaped within an iterative procedure until the generated magnetic field matches the desired magnetic field. The stream-function technique is used to ascertain conductor positions and a method of moments package is then used to finalize the design. An open head/neck coil was designed to operate in a clinical 2T MRI system and the presented results prove the efficacy of this design methodology.