Direct determination of iron in sand using solid sampling graphite furnace atomic absorption spectrometry

A fast and reliable method for the direct determination of iron in sand by solid sampling graphite furnace atomic absorption spectrometry was developed. A Zeeman-effect 3-field background corrector was used to decrease the sensitivity of spectrometer measurements. This strategy allowed working with up to 200 mu g of samples, thus improving the representativity. Using samples with small particle sizes (1-50 mu m) and adding 5 mu g Pd as chemical modifier, it was possible to obtain suitable calibration curves with aqueous reference solutions. The pyrolysis and atomization temperatures for the optimized heating program were 1400 and 2500 degrees C, respectively. The characteristic mass, based on integrated absorbance, was 56 pg, and the detection limits, calculated considering the variability of 20 consecutive measurements of platform inserted without sample was 32 pg. The accuracy of the procedure was checked with the analysis of two reference materials (IPT 62 and 63). The determined concentrations were in agreement with the recommended values (95% confidence level). Five sand samples were analyzed, and a good agreement (95% confidence level) was observed using the proposed method and conventional flame atomic absorption spectrometry. The relative standard deviations were lower than 25% (n = 5). The tube and boat platform lifetimes were around 1000 and 250 heating cycles, respectively.

Direct detection of underivatized chitooligosaccharides produced through chitinase action using capillary zone electrophoresis

Capillary electrophoresis with capacitively coupled contactless conductivity detection was successfully used to quantify N-acetylglucosamine and five N-acetyl-chitooligosaccharides (C2-C6) produced after reaction with a purified chitinase (TmChi) from Tenebrio molitor (Coleoptera). No derivatization process was necessary. The separation was developed using 10 mM NaOH with 10% (v/v) acetonitrile as background electrolyte and homemade equipment with a system that avoids the harmful effect of electrolysis. The limit of detection for all oligosaccharides was ca. 3 mu M, and the results indicated that the larger the oligosaccharide, the higher the sensitivity. Analysis of the chitooligosaccharides produced revealed that TmChi has an endolytic cleavage pattern with C5 as the best substrate (higher catalytic efficiency k(cat)/K-M) releasing C2 and C3. (c) 2007 Elsevier Inc. All rights reserved.

Application of solid sampling device for direct determination of chromium and nickel in lubricating oils by graphite furnace atomic absorption spectrometry

One method using a solid sampling device for the direct determination of Cr and Ni in fresh and used lubricating oils by graphite furnace atomic absorption spectrometry are proposed. The high organic content in the samples was minimized using a digestion step at 400 degrees C in combination with an oxidant mixture 1.0% (v v(-1)) HNO3+15% (v v(-1)) H2O2+0.1% (m v(-1)) Triton X-100 for the in situ digestion. The 3-field mode Zeeman-effect allowed the spectrometer calibration up to 5 ng of Cr and Ni. The quantification limits were 0.86 mu g g(-1) for Cr and 0.82 mg g(-1) for Ni, respectively. The analysis of reference materials showed no statistically significant difference between the recommended values and those obtained by the proposed methods.

Adsorption of the diazo dye Direct Red 23 onto a zinc oxide surface: A spectroscopic study

The adsorption of the diazo dye Direct Red 23 onto a zinc oxide surface at 30 degrees C in the dark was investigated. The color reduction was monitored by spectrophotometry at 503 run. The FTIR and Raman spectra of the Direct Red 23 adsorption as a function of ZnO concentration were registered. From the PM3 semi-empirical calculations of the atomic charge density and dipole moment of the Direct Red 23 molecule, it was demonstrated that the azo, dye molecule may be adsorbed onto the ZnO Surface through molecule geometry modifications, enhancing the interfacial area causing a variation in the bonding frequencies. (C) 2009 Elsevier B.V. All rights reserved.

Rapid and direct determination of glyphosate and aminomethylphosphonic acid in water using anion-exchange chromatography with coulometric detection

A simple, rapid, and low-cost coulometric method for direct detection of glyphosate and aminomethylphosphonic acid (AMPA) in water samples using anion-exchange chromatography and coulometric detection with copper electrode is presented. Under optimized conditions, the limits of detection (LODs) (S/N = 3) were 0.038 mu g ml(-1) for glyphosate and 0.24 mu g ml(-1) for AMPA, without any preconcentration method. The calibration curves were linear and presented an excellent correlation coefficient. The method was successfully applied to the determination of glyphosate and AMPA in water samples without any kind of extraction, clean-up, or preconcentration step. No interferent was found in the water, like this, the recovery was, practically, 100%. (c) 2008 Elsevier B.V. All rights reserved.

Modeling and simulation of the anode in direct ethanol fuels cells

Mathematical modeling has been extensively applied to the study and development of fuel cells. In this work, the objective is to characterize a mechanistic model for the anode of a direct ethanol fuel cell and perform appropriate simulations. The software Comsol Multiphysics (R) (and the Chemical Engineering Module) was used in this work. The software Comsol Multiphysics (R) is an interactive environment for modeling scientific and engineering applications using partial differential equations (PDEs). Based on the finite element method, it provides speed and accuracy for several applications. The mechanistic model developed here can supply details of the physical system, such as the concentration profiles of the components within the anode and the coverage of the adsorbed species on the electrode surface. Also, the anode overpotential-current relationship can be obtained. To validate the anode model presented in this paper, experimental data obtained with a single fuel cell operating with an ethanol solution at the anode were used. (C) 2008 Elsevier B.V. All rights reserved.

Direct Electrochemical Determination of Glyphosate at Copper Phthalocyanine/Multiwalled Carbon Nanotube Film Electrodes

A copper phthalocyanine/multiwalled carbon nanotube film-modified glassy carbon electrode has been used for the determination of the herbicide glyphosate (Gly) at -50 mV vs. SCE by electrochemical oxidation using differential pulse voltamtnetry (DPV). Cyclic voltammetry and electrochemical impedance spectroscopy showed that Gly is adsorbed on the metallic centre of the copper phthalocyanine molecule, with formation of Gly-copper ion complexes. An analytical method was developed using DPV in pH 7.4 phosphate buffer solution, without any pretreatment steps: Gly was determined in the concentration range of 0.83-9.90 mu mol L(-1), with detection limit 12.2 nmol L(-1) (2.02 mu g L(-1))

Simultaneous analysis of five antidepressant drugs using direct injection of biofluids in a capillary restricted-access media-liquid chromatography-tandem mass spectrometry system

Direct analysis, with minimal sample pretreatment, of antidepressant drugs, fluoxetine, imipramine, desipramine, amitriptyline, and nortriptyline in biofluids was developed with a total run time of 8 min. The setup consists of two HPLC pumps, injection valve, capillary RAM-ADS-C18 pre-column and a capillary analytical C 18 column connected by means of a six-port valve in backflush mode. Detection was performed with ESI-MS/MS and only 1 mu m of sample was injected. Validation was adequately carried out using FLU-d(5) as internal standard. Calibration curves were constructed under a linear range of 1-250 ng mL(-1) in plasma, being the limit of quantification (LOQ), determined as 1 ng mL(-1), for all the analytes. With the described approach it was possible to reach a quantified mass sensitivity of 0.3 pg for each analyte (equivalent to 1.1-1.3 fmol), translating to a lower sample consumption (in the order of 103 less sample than using conventional methods). (C) 2008 Elsevier B.V. All rights reserved.

Fluoxetine and norfluoxetine analysis by direct injection of human plasma in a column switching liquid chromatographic system

A column switching LC method is presented for the analysis of fluoxetine (FLU) and norfluoxetine (NFLU) by direct injection of human plasma using a lab-made restricted access media (RAM) column. A RAM-BSA-octadecyl silica (C-18) column (40 min x 4.6 mm, 10 mu m) is evaluated in both backflush and foreflush elution modes and coupled with a C-18 lab-made (50 mm x 4.6 mm, 3 pm) analytical column in order to perform online sample preparation. Direct injection of 100 mu L, of plasma samples is possible with the developed approach. In addition, reduction of sample handling is obtained when compared with traditional liquid-liquid extraction (LLE) and SPE. The total analysis time is around 20 min. A LOQ of 15 ng/mL is achieved in a concentration range of 15-500 ng/mL, allowing the therapeutic drug monitoring of clinical samples. The precision values achieved are lower than 15% for all the evaluated points with adequate recovery and accuracy. Furthermore, no matrix interferences are found in the analysis and the proposed method shows to be an adequate alternative for analysis of FLU in plasma.

The impact of foreign direct investment and openness on Vietnamese economy

This thesis examines the impact of foreign direct investment (FDI) on Vietnamese economy based on Partial Adjustment Model and time series data from 1976 to 2004. FDI is shown to have not only short run but also long run effect on gross domestic product (GDP) of Vietnam. However, elasticity of GDP with respect to FDI is small and it will take many years to fully manifest itself. The impact of trade openness on GDP has also been examined and it is shown to be stronger than that of FDI. The paper offers a number of explanations and discusses briefly suggestions in order to increase the contribution of FDI to Vietnam’s economic development.

The Impact of Foreign Direct Investment on International Trade: An Empirical Study of China

This paper investigates the impact of inward FDI (Foreign Direct Investment) on international trade of China empirically on the country level by using panel data from 1984 to 2007. Two separate transformed models which are based on the gravity equation and refer to the econometric models of some previous studies, are used in this paper to estimate the effect of FDI inflows on exports and imports respectively. The estimation results confirmed the complementary relationship between FDI inflows and trade of China both on exports and imports, which has also been supported by previous empirical studies.

Solar Energy assessment based on weather station data for direct site monitoring in Indonesia

This thesis evaluates different sites for a weather measurement system and a suitable PV- simulation for University of Surabaya (UBAYA) in Indonesia/Java. The weather station is able to monitor all common weather phenomena including solar insolation. It is planned to use the data for scientific and educational purposes in the renewable energy studies. During evaluation and installation it falls into place that official specifications from global meteorological organizations could not be meet for some sensors caused by the conditions of UBAYA campus. After arranging the hardware the weather at the site was monitored for period of time. A comparison with different official sources from ground based and satellite bases measurements showed differences in wind and solar radiation. In some cases the monthly average solar insolation was deviating 42 % for satellite-based measurements. For the ground based it was less than 10 %. The average wind speed has a difference of 33 % compared to a source, which evaluated the wind power in Surabaya. The wind direction shows instabilities towards east compared with data from local weather station at the airport. PSET has the chance to get some investments to investigate photovoltaic on there own roof. With several simulations a suitable roof direction and the yearly and monthly outputs are shown. With a 7.7 kWpeak PV installation with the latest crystalline technology on the market 8.82 MWh/year could be achieved with weather data from 2012. Thin film technology could increase the value up to 9.13 MWh/year. However, the roofs have enough area to install PV. Finally the low price of electricity in Indonesia makes it not worth to feed in the energy into the public grid.

An analysis of linkage between foreign direct investment and GDP per Capita in Pakistan : A time series analysis

This study aims to investigate the relation between foreign direct investment (FDI) and per capita gross domestic product (GDP) in Pakistan. The study is based on a basic Cobb-Douglas production function. Population over age 15 to 64 is used as a proxy for labor in the investigation. The other variables used are gross capital formation, technological gap and a dummy variable measuring among other things political stability. We find positive correlation between GDP per capita in Pakistan and two variables, FDI and population over age 15 to 64. The GDP gap (gap between GDP of USA and GDP of Pakistan) is negatively correlated with GDP per capita as expected. Political instability, economic crisis, wars and polarization in the society have no significant impact on GDP per capita in the long run.