Fotocatálise heterogênea com TiO2 para oxidação de arsênio e sua remoção de águas por coprecipitação com sulfato férrico

The oxidation of arsenic (As(III) to As(V)) in water samples was performed by heterogeneous photocatalysis using a TiO2 film immobilized inside a photochemical reactor. After oxidation, As(V) was removed from the water samples by coprecipitation with ferric sulfate. The final conditions of oxidation and arsenic removal (TiO2 film prepared with a suspension: 10% (w/v); pH: 7.0; oxidation time: 30 min and Fe3+ concentration: 50 mg L-1) were applied in natural water samples which were supplemented with 1.0 mg L-1 of As(III) to verify the influence of the matrix. After treatment, more than 99% of arsenic was removed from the water.

Caracterização do MP10 e MP2,5 e distribuição por tamanho de cloreto, nitrato e sulfato em atmosfera urbana e rural de Londrina

Samplings of atmospheric particulate matter (PM) were carried out between the months of March and April of 2007, simultaneously in two areas of Londrina, an urban (Historical Museum) and other rural (Farm School-UEL). PM was collected using the cascade impactor consisting of four impaction stages (0.25 to 10 μm). The results indicated that the fine fraction (PM2.5) represented a significant portion of the mass of PM10 (70 and 67% in the urban and rural places, respectively). Cl-, NO3- and SO4(2-) were determined by ion chromatography and the size distribution is presented. Natural and anthropogenic sources were suggested to the ionic components in the fine and coarse mode of PM.

Determinação de paracetamol pela inibição da reação quimiluminescente do luminol-hipoclorito de sódio em um sistema de análise em fluxo empregando o conceito de multicomutação

A flow injection chemiluminescence method for the determination of paracetamol in pharmaceutical formulations is described. It is based on the consumption of the sodium hypochlorite by paracetamol and decreases of the analytical signal. The analytical curve was linear in the paracetamol concentration range from 5.0 x 10-6 to 5.0 x 10-5 mol L-1, with a detection limit of 1.8 x 10-6 mol L-1. The RSDs were 2.0 and 1.2% respectively for 2.0 x 10-5 and 4.0 x 10-5 mol L-1 paracetamol solutions (n = 10) and a sampling frequency of 180 h-1 was obtained.

Caracterização da fusão peritética do cloreto de sódio di-hidratado por curvas de aquecimento

Binary mixture phase diagrams are normally obtained from thermal analysis involving freezing point curves. However, that approach is not always reliable and easy to follow to all kinds of mixtures in any proportion. In fact, even for a simple system, such as NaCl-H2O, this freezing methodology gives mixed results when one starts from a solid-solution system, due mostly to the formation of the NaCl.2H2O, which has an incongruent melting point, and the dependence of its solubility with the temperature. In this work we report a trustworthy, simple and cheap method involving heating curves to drawn the NaCl-H2O phase diagram.

Efeito da aplicação de nitrato na redução biogênica de sulfeto sob diferentes concentrações iniciais de bactérias redutoras de nitrato e sulfato

The effect of sodium nitrate application in the reduction of biogenic sulphide was evaluated through a 2k complete factorial design, using as variable response the production of sulfide at intervals of incubation of 7, 14 and 28 days. The most effective condition for reducing the sulphide production (final concentrations from 0.4 to 1.6 mg S2- L-1) was obtained with an initial population of sulphate-reducing bacteria and nitrate-reducing bacteria of 10(4) MPN mL-1 and 427.5 mg L-1 nitrate. The results also suggested that the applications of nitrate to control the process of souring should follow a continuous scheme.

Influência da temperatura, umidade e profundidade do solo na persistência do diurom e sulfato de endossulfam em um solo tropical

The influence of temperature (30 and 40 ºC) and soil humidity (20, 50 and 70% of water holding capacity) on the degradation of the herbicide diurom and the endosulfan metabolite, endosulfan sulfate was studied under laboratory conditions, in different soil layers (0-30, 30-38 and 38-83 cm) of an Oxisol (Yellow Latosol) collected in an agricultural area of Mato Grosso State, Brazil. Endosulfan sulfate was rapidly degraded under lower soil humidity, higher temperature and deeper soil layers. For diurom the opposite was observed as a consequence of its higher water solubility and lower soil sorption coefficient.

Descoloração redutiva de corantes azo e o efeito de mediadores redox na presença do aceptor de elétrons sulfato

We investigated the impact of sulphate and the redox mediator Anthraquinone-2,6-disulfonate (AQDS) on the decolorization of the azo dyes Congo Red (CR) and Reactive Black 5 (RB5). In anaerobic reactors free of extra sulphate dosage, the color removal efficiency decreased drastically when the external electron donor ethanol was removed. In presence of an extra dosage of sulphate, CR decolourisations were 47.8% (free of AQDS) and 96.5% (supplemented with AQDS). The decolourisations achieved in both reactors with RB5 were lower than the ones found with CR. Finally, the biogenic sulphide contribution on azo dye reduction was negligiable.

Fracionamento de polifosfato de sódio e caracterização por RMN de 31P: um experimento para aulas de físico-química

This text describes an experiment on fractional precipitation of a polymer together with determination of average degree of polymerization by NMR. Commercial sodium polyphosphate was fractionated by precipitation from aqueous solution by adding increasing amounts of acetone. The polydisperse salt and nine fractions obtained from it were analyzed by 31P Nuclear Magnetic Resonance and the degree of polymerization of the salts and of the fractions were calculated. Long-chain sodium polyphosphate was also synthesized and analyzed. This experiment was tested in a PChem lab course but it can be used also to illustrate topics of inorganic polymers and analytical chemistry.

Reação da cânfora com boroidreto de sódio: uma estratégia para o estudo da estereoquímica da reação de redução

Reduction of camphor to a mixture of borneol and isoborneol was performed using NaBH4 as the reducing agent under suitable conditions. Although more effective reduction was accomplished using toxic methanol, an alternative non-toxic ethanolic system is described. This experiment is important to introduce undergraduate students in reductive procedures, and can be used to show details on stereoselective procedures on carbonyl moieties (facial diastereoselectivity, Bürgi-Dunitz trajectory, diastereomeric excess).

Autoassociação de misturas dos Surfactantes Dodecanoato de Sódio (SDoD) e Decanoato de Sódio (SDeC) com o Polímero Hidrofobicamente Modificado Etil(Hidroxietil)Celulose (EHEC)

In this work, the interactions between the non-ionic polymer of ethyl(hydroxyethyl)cellulose (EHEC) and mixed anionic surfactant sodium dodecanoate (SDoD)-sodium decanoate (SDeC) in aqueous media, at pH 9.2 (20 mM borate/NaOH buffer) were investigated by electric conductivity and light transmittance measurements at 25 ºC. The parameters of the surfactant to polymer association processes such as the critical aggregation concentration and saturation of the polymer by surfactants were determined from plots of specific conductivity vs total surfactant concentration, [surfactant]tot = [SDoD] + [SDeC]. Through the results was not observed a specific link of polymer with the surfactant, implying therefore a phenomenon only cooperative association.

Mobilidade de bário em solo tratado com sulfato de bário sob condição de oxidação e redução

In order to evaluate possible solubility of BaSO4 in soils under reducing conditions, column leaching assay was settled down, where the soil received three doses of BaSO4 (100, 300 and 3000 mg kg-1) at two humidities. After reaching an Eh of -200 mV rainfall of 200 mm per day-1 was simulated. The condition of reduction led to the increased levels of barium in the fractions of higher lability and the highest levels of barium in the leachate extract, which were above the potability standards. Only 0.05% of barium in the column that received the highest dose was removed by leaching.

Modelagem termodinâmica por extração por solvente de metais divalentes em meio sulfato usando D2EHPA

The extraction of divalent metals (Mn2+, Ni2+, Co2+ and Cu2+) in the system MSO4 - H2SO4 - H2O - D2EHPA in isoparaffin (17/21) was studied by a thermodynamic model based on chemical equilibria with mass and charge balance equations. The activity coefficients of all solutes in the aqueous phase were calculated by Davies equation. By applying this model, the equilibrium concentrations of solutes were calculated from de concentration of divalent metals and pH. The predicted distribution coefficients for the divalents metals were in good agreement with experimental results.

Investigating the spontaneous formation of SDS micelle in aqueous solution using a coarse-grained force field

A 1µs Molecular Dynamic simulation was performed with a realistic model system of Sodium Dodecyl Sulfate (SDS) micelles in aqueous solution, comprising of 360 DS-, 360 Na+ and 90000 water particles. After 300 ns three different micellar shapes and sizes 41, 68 and 95 monomers, were observed. The process led to stabilization in the total number of SDS clusters and an increase in the micellar radius to 2.23 nm, in agreement with experimental results. An important conclusion, is be aware that simulations employed in one aggregate, should be considered as a constraint. Size and shape distribution must be analyzed.

Determinação de bussulfano em plasma através de cromatografia líquida de alta eficiência com detector de arranjo de diodos e derivatização com dietilditiocarbamato de sódio

A high performance liquid chromatographic-diode array detection method for the determination of busulfan in plasma was developed and validated. Sample preparation consisted of protein precipitation followed by derivatization with sodium diethyldithiocarbamate and liquid-liquid extraction with methyl-tert-butyl ether. Chromatograms were monitored at 277 nm. Separation was carried out on a Lichrospher RP 18 column (5 µm, 250 x 4 mm). The mobile phase consisted of water and acetonitrile (20:80, v/v). The method presented adequate specificity, linearity, precision and accuracy and allowed reliable determination of busulfan in clinical plasma samples, being applied to three patients submitted to bone marrow transplantation.

Montagem de uma prensa para fios de sódio metálico

Several organic chemistry labs in Brazil suffers from the absence of a safe method to extrude sodium wire, used to obtain anhydrous solvents such as THF or ethyl ether. This technical note presents the assembly instructions for a sodium wire press, similar to the one that has been used for the past four years in our laboratory without any maintenance.