Determinação de benzeno, tolueno, etilbenzeno e xilenos em gasolina comercializada nos postos do estado do Piauí

Automotive gasoline consists of a complex mixture of flammable and volatile hydrocarbons derived from crude oil with carbon numbers within the range of 4-12 and boiling points range of 30-225 ºC. Its composition varies with the kind of crude oil and the type of refinery process that they undergone. Aromatics hydrocarbons, in particular benzene, toluene, ethylbenzene and isomeric xylenes (BTEX) are the toxic group constituents presents. GC-FID was employed to quantify these hydrocarbons in 50 commercial gasoline samples from Piauí state. Statistical analysis techniques, such as PCA and HCA were used to analyze the data. Moreover, several validation parameters were evaluated.

The use of tribromoisocyanuric acid to distinguish among primary, secondary and tertiary alcohols

Primary, secondary and tertiary alcohols can be easily distinguished due to their reactivity towards tribromoisocyanuric acid (TBCA). The test is performed by adding TBCA to the alcohol in a test tube heated in a boiling water bath. Orange color develops in the tube containing the primary alcohol, light yellow is observed in the tube containing the secondary alcohol while the tertiary alcohol results in a colorless mixture.

Sonication-assisted preparation of CaO nanoparticles for antibacterial agents

The effect of calcination conditions on the size and killing activity of CaO nanoparticles towards L. plantarum was studied in this paper. The results showed that CaO nanoparticles with a diameter of 20 nm could be obtained under the investigated conditions. The lethal effect of CaO nanoparticles after incubation of 6 or 24 h increased with increasing calcination time. Using CaO-SA, CaO-SB, and CaO-SC after a 24-h exposure, 2.25, 3.37, and 5.97 log L. plantarum were killed, respectively, at a concentration of 100 ppm. The current results show that the use of CaO nanoparticles as antibacterial agents has significant potential in food-relevant industries.

Resgatando um método eficiente para determinação do ponto de ebulição de substâncias orgânicas: percolador versus Siwoloboff

The aim of this paper was to revive the accurate determination of the boiling point of organic compounds using the percolator technique developed in the 1960s. Although this method is simple, fast and efficient it is omitted from current textbooks. This method has several advantages over Siwoloboff such as high reproducibility and direct measurement of the boiling point of the sample obtained by observing the temperature of the vapor-liquid equilibrium. The experiments were performed in the organic chemistry laboratory but allow interdisciplinary integration with other disciplines of several academic areas.

Interação de complexo de rutênio com albumina de soro bovino para detecção amperométrica de ácido ascórbico

The binding of [Ru(PAN)(PPh3)2(ISN)]Cl (PAN = 1-(2'-Pyridylazo)-2-naphtholate) to bovine serum albumin (BSA) was investigated by spectroscopic techniques. According to analysis of the results from the Stern-Volmer equation, the ruthenium complex is able to quench the fluorescence intensity of BSA via a dynamic mechanism. The thermodynamic parameters were calculated (ΔH = 30.3 kJ mol-1; ΔS = 195.4 J mol-1 K-1), indicating that hydrophobic force is the main interaction driving force. The site marker competitive experiments revealed that the binding site of ruthenium complex was in the sub-domain IIA of BSA. FTO glass with a film of BSA-[Ru(PAN)(PPh3)2(ISN)]Cl was used as an ascorbic acid sensor. The linear range of the modified electrode was between 1 and 8 × 10-6 mol L-1.

DETERMINAÇÃO DE Cd E Pb EM AMOSTRAS DE GOMA XANTANA POR GF AAS

This paper describes the evaluation of a method for determination of Cd and Pb in xanthan gum samples by Graphite Furnace Atomic Absorption Spectrometry (GF AAS) using NH4H2PO4 as the chemical modifier. The sample preparation was performed using a reflux system adapted in the digestion tubes. With this system it was possible to increase the temperature of the digester block above the boiling point of the reaction medium, preventing loss of analyte and excessive evaporation of acids during heating. Samples were digested with HNO3 for 3 h in a digester block at 220 ºC. The limits of detection for Cd and Pb were 2.2 and 33.8 ng g-1, respectively. The RSDs for both analytes were, on average, lower than 5.0% and accuracy was verified by recovery tests, yielding values in the 83-100% range.

Use of experimental design in the optimisation of a solid phase preconcentration system for Cobalt determination by GFAAS

In this work is proposed a solid phase preconcentration system of Co2+ ions and its posterior determination by GFAAS in which fractional factorial design and response surface methodology (RSM) were used for optimization of the variables associated with preconcentration system performance. The method is based on cobalt extraction as a complex Co2+-PAN (1:2) in a mini-column of polyurethane foam (PUF) impregnated with 1-(2-pyridylazo)-naphthol (PAN) followed by elution with HCl solution and its determination by GFAAS. The chemical and flow variables studied were pH, buffer concentration, eluent concentration and preconcentration and elution flow rates. Results obtained from fractional factorial design 2(5-1) showed that only the variables pH, buffer concentration and interaction (pH X buffer concentration) based on analysis of variance (ANOVA) were statistically significant at 95% confidence level. Under optimised conditions, the method provided an enrichment factor of 11.6 fold with limit of detection and quantification of 38 and 130 ng L-1, respectively, and linear range varying from 0.13 to 10 µg L-1. The precision (n = 9) assessed by relative standard deviation (RSD) was respectively 5.18 and 2.87% for 0.3 and 3.0 µg L-1 cobalt concentrations.

[Koska meillä on joulu] : [orkesterihupailu]

Soitinnus: orkesteri.

[Duetto Parigi o cara oopperasta La Traviata]

Soitinnus: lauluäänet (sopraano, tenori), orkesteri.

[Duetto Teco io sto oopperasta Naamiohuvit]

Soitinnus: lauluäänet (sopraano, tenori), orkesteri.

[Aaria oopperasta Sevillan parturi]

Soitinnus: lauluääni (sopraano), orkesteri.

[Aaria oopperasta Lucia di Lammermoor]

Soitinnus: lauluääni (sopraano), orkesteri.

[Pyhäaamun rauha]

Soitinnus: naiskuoro, jouset, piano.