Determination of As, Cd, Pb and Se in DORM-1 dogfish muscle reference material using alkaline solubilization and electrothermal atomic absorption spectrometry with Ir+Rh as permanent modifiers or Pd+Mg in solution

In this work, tetramethylammonium hydroxide (TMAH) was used to solubilize the DORM-1 dogfish muscle certified reference material as a model substance for the determination of As, Cd, Pb and Se by electrothermal atomic absorption spectrometry (ET AAS). The sample was mixed with a small amount of TMAH and heated to 60 °C for 10 min in a water bath. After dissolution, As and Se were determined using palladium and magnesium nitrates as a chemical modifier added in solution. For Cd and Pb, best results were obtained with a mixture of 250 μg of each of iridium and rhodium as permanent modifiers. In both cases, the calibration was performed with aqueous solutions in 0.2% v/v HNO₃. The temperature program for each analyte was optimized using pyrolysis and atomization curves established with the fish reference material. The detection limits in dry samples and the characteristic mass values were: Cd 0.005 μg g⁻¹ and 0.9 pg; Pb 0.04 μg g⁻¹ and 7.6 pg; As 0.4 μg g⁻¹ and 13 pg and Se 0.6 μg g⁻¹ and 20 pg, respectively. Results from the determination of these elements in the DORM-1 certified fish reference material were within the 95% confidence interval of the certified values.     

Stability of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al in ionic liquid BMI.BF<Subscript>4</Subscript>/γ-butyrolactone electrolytes for use in electrolytic capacitors

The stability of aluminium oxide has been investigated in mixtures of ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF₄) and γ-butyrolactone (GBL) for application as the impregnation electrolyte of aluminium electrolytic capacitors. Ionic conductivity measurements of BMI.BF₄/GBL electrolytes at different temperatures were performed, as well as electrochemical impedance spectroscopy and cyclic voltammetry experiments. The results show that the highest ionic conductivity value of 40 mS cm^?1 (70 °C) is achieved in electrolyte x _BMI.BF4 = 0.2. The total capacitance values, associated with the dielectric oxides, vary between 1 and 8 μF cm^?2 for all studied electrolytes after 30 days of immersion. The polarization resistance and total capacitance of the electrolyte/Al₂O₃/Al system decrease slightly with immersion time, showing the stability of Al₂O₃/Al in ionic liquid BMI.BF₄/GBL electrolytes.     

Fully automated multianalyte determination of different classes of pesticides,at picogram per litre levels in water,by on-line solid-phase extraction–liquid chromatography–electrospray–tandem mass spectrometry

This paper reports the development of a fully automated method for the multianalyte determination of twenty pesticides belonging to different classes (triazines, phenylureas, organophosphates, anilines, acidic, propanil, and molinate) in natural and treated waters. The method, based on on-line solid-phase extraction–liquid chromatography–electrospray–tandem mass spectrometry, is highly sensitive (limits of detection between 0.004 and 2.8 ng L^–1), precise (relative standard deviations between 2.0 and 12.1%), reliable (two selected reaction-monitoring transitions are monitored per compound), rapid (45 min per sample), and simple. The application of this method to the monitoring of the target compounds in a waterworks revealed the presence of the pesticides investigated at concentrations up to 516 and 82 ng L^–1 (total pesticide concentration) in river water and ground water, respectively, used as sources, and their gradual removal through the purification process.Dedicated to the memory of Wilhelm Fresenius     

Automated determination of tin and nickel in brass by on-line anodic electrodissolution and electrothermal atomic absorption spectrometry

The application of an on-line metallic alloy dissolution system using anodic electrodissolution in a flow injection system for the determination of tin and nickel in copper alloys is described. After the electrolyzed material was collected in the autosampler cup, determination was carried out using electrothermal atomic absorption spectrometry (ETAAS). Using specific software developed in Turbo Pascal 7.0, it is possible to control electrolysis time, intensity of the applied current, and triggering of the three-way solenoid valves that push the fluids. Through manipulation of these variables, it is possible to adjust the analytical signal to within the working range of the spectrometer. Calibration of the spectrometer was accomplished by processing reference material. For tin, relative standard deviations for a series of measurements (n=5) performed on the same point and on different points of the sample was smaller than 2 and 4%, respectively; for nickel, 2 and 5%, respectively. The results for tin and nickel were in good agreement with those obtained through application of the classical methodology, as well as with data obtained by optical emission spectrometry. The detection limit for tin was 0.001% (w/w), whereas for nickel it was 0.003% (w/w). The analytical throughput is 30 samples h⁻¹.     

Analysis of the role of the calculator in Brazilian textbooks

This paper presents the results of an investigation in which 48 textbooks have been analysed, to observe whether and how primary school textbooks approved by the Brazilian national textbook programme (Programa Nacional do Livro Didático—PNLD) consider the use of calculators. It has been noticed that many textbooks recommend the use of calculators in the classroom and suggest specific activities. In the PNLD teacher’s guide, only in the analysis of some textbooks is there clear information on calculator usage in the classroom. Calculator usage is mainly encouraged in the textbooks of the final years in primary school, mostly with multiplication and division, and distributed in four types of activities: conceptual development, verification of results, results calculation and calculator tool manipulation. Many textbooks have considered the recommendation to use modern technological devices to aid the learning of mathematics, while others still have to assess the value of the calculator as a valid instrument in developing mathematical knowledge.     

Suppression of plasma turbulence during optimized shear configurations in JET

Correlation of density turbulence suppression and reduced plasma transport is observed in the internal transport barrier (ITB) region of JET tokamak discharges with optimized magnetic shear. The suppression occurs in two stages. First, low frequency turbulence and ion transport are reduced across the plasma core by a toroidal velocity shear generated by intense auxiliary heating. Then with the ITB formation, high frequency turbulence and electron transport are reduced locally within the steep pressure gradient region of the ITB.     

Matrix isolation FTIR spectroscopic and theoretical study of dimethyl sulfite

The preferred conformations of dimethyl sulfite and their vibrational spectra were studied by matrix-isolation Fourier transform infrared spectroscopy and theoretical methods (density functional theory (DFT) and Moller-Plesset (MP2), with basis sets of different sizes, including the quadruple-zeta, aug-cc-pVQZ basis). Five minima were found at these levels of theory. At the MP2/6-31++G(d,p) and DFT/B3LYP/aug-cc-pVQPZ levels, the GG conformer (where the O-S-O-C dihedral angles are 73.2 and 70.8 degrees ) resulted in the conformational ground state. At the highest level of theory used, the GT conformer (O-S-O-C = +68.5 and -173.2 degrees ) is 0.83 kJ mol(-1) higher in energy than the GG form, while conformer GG' (O-S-O-C = +85.7 and -85.7 degrees ) has a relative energy of 1.18 kJ mol(-1). The remaining two conformers (G'T and TT) are high-energy forms and not experimentally relevant. In consonance with the theoretical predictions, conformer GG was found to be the most stable conformer in the gaseous phase as well as in the low-temperature matrices. Annealing of the argon matrices first promotes the GG'-->GT isomerization, which is followed by conversion of GT into the most stable conformer. There is no evidence of occurrence of GG'-->GG direct conversion in the low-temperature matrices. On the other hand, during deposition of the xenon matrices conformer GG' totally converts to conformer GT. Two observations demonstrated this fact: no evidence of bands corresponding to GG' were observed in xenon matrices and the GG/GT intensity ratio became similar to the GG/(GT + GG') intensity ratio observed in argon matrices. All these results could be explained by taking into account the relative values of the theoretically predicted energy barriers for the different isomerization processes: GG'-->GT, 1.90 kJ mol(-1); GT-->GG, 9.64 kJ mol(-1); and GG'-->GG, 19.46 kJ mol(-1).     

Synthesis of 4-amino-2,6-diaryl-5-cyanopyrimidines as antimicrobial agents

This article describes an efficient and facile synthesis of 11 2,4,6-trisubstituted 5-cyanopyrimidines starting from meta- and para-substituted 2-cyanocinnamonitriles and arylamidines. The synthesized heterocycles, 3a–k, were characterized by infrared (IR), ¹H NMR, ¹³C NMR, and mass spectral data. The probable mechanism of formation of the title compounds employing 2-cyanocinnamonitriles and arylamidines in the presence of a base was clarified. A preliminary screening of the antibacterial tests clearly showed that 4 out of 11 pyrimidines, 3a, 3e, 3f, and 3k, were effective against bacteria Staphyloccus aureus, Bacillus subtillis, and Pseudomonas aeruginosa. Further, the minimum inhibitory concentration (MIC) against the bacteria has been determined.     

Multianalyte determination of different classes of pesticides (acidic,triazines, phenyl ureas,anilines, organophosphates,molinate and propanil) by liquid chromatography-electrospray-tandem mass spectrometry

This work describes the optimization of a liquid chromatography-electrospray-tandem mass spectrometry (LC-ESI-MS-MS) method for the multianalyte determination of twenty pesticides, selected based on current regulations and extent of use. Chromatographic separation was carried out on a Purospher STAR RP-18e column using gradient acetonitrile-water as mobile phase. Triazines, phenylureas, organophosphates, anilines, and molinate were determined in the positive ionization mode, and acidic pesticides and propanil in the negative ion mode. Two different precursor ion-product ion transitions were selected for each analyte and monitored under time scheduled multiple reaction monitoring (MRM) conditions. The optimized method was shown to be linear in the range 1 to 1000 ng/mL with correlation coefficients higher than 0.99 for all but one (diazinon) of the analytes, very sensitive (with limits of detection between 0.010 and 4.528 ng/mL), and repeatable (with relative standard deviations, calculated from the replicate analysis of standard mixtures, lower than 14%). The present work was also devoted to the elucidation of the structures of the principal fragment ions obtained after collision-induced dissociation of the pesticides investigated, an aspect often overlooked in the literature.     

Determination of As and Sb in Steels by Electrothermal Atomic Absorption Spectrometry after Reduction, Complexation and Sorption on Activated Carbon

 A method for the preconcentration and separation of As and Sb in steel sample solutions is proposed. The analytes are reduced to their trivalent oxidation states with a mixture of ascorbic acid and potassium iodide and complexed by the ammonium salt of dithiophosphoric acid O,O-diethyl ester. The complexes are sorbed onto carbon. After desorption in a small volume of nitric acid solution, As and Sb are determined by electrothermal atomic absorption spectrometry. Iron(III) is also reduced to Fe(II), which is not complexed and is about 99.9% eliminated by the preconcentration procedure. Enrichment factors of 5 and 10 were obtained for As and Sb, respectively. The method was applied to the analysis of four certified steel samples, after acid dissolution in a microwave system and good agreement was obtained with the certified values. Received May 4, 1998. Revision February 22, 1999.