Aumento da resposta analítica por meio da otimização do sistema de injeção sem divisão de fluxo em cromatografia gasosa empregando a lei dos gases ideais

This paper reports the development of an easy, fast and effective procedure for the verification of the ideal gas law in splitless injection systems in order to improve the response. Results of a group of pesticides were used to demonstrate the suitability of the approach. The procedure helps establish experimental parameters through theoretical aspects. The improved instrumental response allowed extraction with lower sample volumes, the minimization of time and costs and the simplification of sample preparation.

Simulação Monte Carlo de mecanismo de transferência de energia de excitação eletrônica: modelo de Perrin para a supressão estática da luminescência

A software based in the Monte Carlo method has been developed aiming the teaching of the Perrin´s model for static luminescence quenching. This software allows the student to easily simulate the luminescence decays of emissive molecules in the presence of quenching ones. The software named PERRIN was written for FreeBASIC compiler and it can be applied for systems where the molecules remain static during its excited state lifetime. The good agreement found between the simulations and the expected theoretical results shows that it can be used for the luminescence and excited states decay kinetic teaching.

Análise por injeção em fluxo com detecção amperométrica de múltiplos pulsos: potencialidades e aplicações

The potentialities and applications of the Multiple Pulse Amperometric detection (MPA) coupled with Flow Injection Analysis (FIA) are evaluated. Important aspects as cleaning and activation of electrode surface, indirect and simultaneous analysis of electroactive compounds and the use of the internal standard method for quantifications utilizing FIA-MPA are presented. The main parameters concerning the detection of electroactive analytes by multiple pulse amperometric detection in flowing solutions were also discussed. In addition, aspects such as flow rate, sample volume, application time of the potential pulses and instrumentation necessary for implementing of the method were also addressed.

Organic and total mercury determination in sediments by cold vapor atomic absorption spectrometry: methodology validation and uncertainty measurements

The purpose of the present study was to validate a method for organic Hg determination in sediment. The procedure for organic Hg was adapted from literature, where the organomercurial compounds were extracted with dichloromethane in acid medium and subsequent destruction of organic compounds by bromine chloride. Total Hg was performed according to 3051A USEPA methodology. Mercury quantification for both methodologies was then performed by CVAAS. Methodology validation was verified by analyzing certified reference materials for total Hg and methylmercury. The uncertainties for both methodologies were calculated. The quantification limit of 3.3 µg kg-1 was found for organic Hg by CVAAS.

Simulação do intemperismo natural de pilhas zinco-carbono e alcalinas

Spent alkaline and Zn-C batteries were placed in seawater, rainwater or landfill leachate at room temperature for up 30 days in order to simulate natural weathering. After the experiments pH and electrical conductivity of the liquid were measured. The precipitate formed and the filtrate were submitted to metal analysis by ICP-OES. Seawater is the most corrosive medium, followed by landfill leachate. Pb, Cd and Hg were mainly in the filtrate. Fe, Mn and Zn were generally dominant in the precipitate. Na and K account for the electrical conductivity and are good indicators of the corrosion stage of the batteries.

Determinação espectrofotométrica por injeção em fluxo de glifosato em formulações comerciais de herbicidas

A flow injection spectrophotometric procedure for the determination of glyphosate in commercial formulations of herbicides is proposed. The determination is based on the reaction of glyphosate and p-dimethylaminocinnamaldehyde, in acid medium, yielding a colored compound (l máx = 495 nm). Under optimal conditions, Beer's law is obeyed in a concentration range 40-640 mg mL-1 with a correlation coefficient of 0.9996. The detection limit was 8.60 mg mL-1 for glyphosate. The method was successfully applied for the determination of glyphosate in commercial formulations of herbicides. Recovery of glyphosate from various commercial samples of herbicides range from 91.0 to 110%.

Efeito da adição de lantânio em catalisadores de Ni/ZrO2 aplicados na reação de reforma a vapor de etanol

The catalytic performance of Ni/ZrO2 catalysts loaded with different lanthanum content for steam reforming of ethanol was investigated. Catalysts were characterized by BET surface area, X-ray diffraction, UV-vis spectroscopy, temperature programmed reduction, and X-ray absorption fine structure techniques. Results showed that lanthanum addition led to an increase in the degree of reduction of both NiO and nickel surface species interacting with the support, due to the higher dispersion effect. The best catalytic performance at 450 ºC was found for the Ni/12LZ catalyst, which exhibited an effluent gaseous mixture with the highest H2 yield.

Determinação simultânea de ácido ascórbico e ácido acetilsalicílico usando análise por injeção em fluxo com detecção amperométrica pulsada

A simple flow system with multiple pulse amperometric detection using a single working electrode is proposed for simultaneous determination of ascorbic (AA) and acetylsalicylic (AAS) acids in pharmaceutical formulations. The procedure is based on application of two potential pulses: 0.90 V/50 ms: oxidation and determination of AA without the interference of AAS; 1.35 V/50 ms: oxidation of both compounds and quantification of AAS by current subtraction using a correction factor. Sampling rate was estimated as 125 injections per hour and the limits of detection were 0.17 and 0.16 µmol L-1 for AA and AAS, respectively. Results for commercial samples agreed with those obtained using HPLC.

Efeito do teor de umidade sobre o pré-tratamento a vapor e a hidrólise enzimática do bagaço de cana-de-açúcar

The effect of moisture content in the steam treatment and enzymatic hydrolysis of sugarcane bagasse was evaluated. Steam treatment was perfomed at 195-210 ºC for 4-8 min using cane bagasse with moisture contents in the range 16-100 wt% (dry basis). Increased moisture contents not only had a positive influence in recovery of main cane biomass components but also resulted in better substrates for enzymatic hydrolysis. As a result, drying is not required for optimal pretreatment and enzymatic hydrolysis of sugarcane bagasse, which can be processed into second generation ethanol immediately after crushing and hot water washing.

Determinação rápida de hidroquinona usando análise por injeção em batelada (BIA) com detecção amperométrica

A fast analytical method for determination of hydroquinone in pharmaceutical formulations employing batch injection analysis (BIA) with amperometric detection using a boron-doped diamond electrode is described. The supporting electrolyte was a 0.1 mol L-1 H2SO4 solution (the single reagent used for analysis). The method showed good repeatability (RSD of 0.45%, n=20), wide linear range (from 10 to 2000 µmol L-1, R=0.9999), low detection limit (0.016 µmol L-1) and satisfactory recovery values (91-96%). Accuracy of the method was evaluated by comparative analyses using high-performance liquid-chromatography. The ability to replace the electronic pipette by disposable syringes (injection procedure) in BIA systems was also shown.

Cristalización de zeolita beta mediante conversión asistida por vapor: influencia de los parámetros de síntesis

In the present work, beta zeolites were prepared by an alternative route called steam-assisted conversion (SAC). Several zeolites were synthesized using amorphous dry gels with a low SDA concentration (0.09 mol, TEAOH). Temperature and crystallization time were the main parameters studied. X-ray diffraction (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM) were the characterization techniques employed. The zeolites prepared showed mixed phases such as beta, MTW and ZSM-5 while only one sample treated at 150ºC with 24 h of crystallization time showed a pure ZSM-5 phase (SAC-5). These preliminary results serve as a starting point for optimizing the synthesis of a specific type of zeolite using the SAC method.

PCA: uma ferramenta para identificação de traçadores químicos para água de formação e água de injeção associadas à produção de petróleo

This study describes the use of Principal Component Analysis to evaluate the chemical composition of water produced from eight oil wells in three different production areas. A total of 609 samples of produced water, and a reference sample of seawater, were characterized according to their levels of salinity, calcium, magnesium, strontium, barium and sulphate (mg L-1) contents, and analyzed by using PCA with autoscaled data. The method allowed the identification of variables salinity, calcium and strontium as tracers for formation water, and variables magnesium and sulphate as tracers for seawater.

Determinação de nimesulida por análise por injeção em fluxo com detecção amperométrica de múltiplos pulsos

A simple and fast method for the determination of nimesulide (NI) using flow injection analysis with multiple-pulse amperometric (FIA-MPA) detection at a boron-doped diamond (BDD) electrode was developed. The method was based mainly on the application of a four-potential waveform, E1(det) = -0.8 V / 30 ms, E2(det) = 0.6 V / 30 ms, E3(det) = -0.4 V / 30 ms and E4(cleaning) = -0.45 V / 300 ms versus Ag/AgCl (3.0 mol L-1 KCl). NI was detected at three different electrode potentials, at which the nitro group undergoes different redox reactions. The proposed method was selective and sensitive (detection limit of 81.0 nmol L-1), and successfully applied for the determination of NI in pharmaceutical formulations, yielding similar results to those obtained by the reference method.

Software para simulação de mecanismo de supressão da luminescência: modelo cinético de Stern-Volmer

A software that includes both Stochastic and Molecular Dynamics procedures has been developed with the aim of visualizing the Stern-Volmer kinetic mechanism of dynamic luminescence quenching. The software allows the student to easily simulate and graphically visualize the molecular collisions, the molecular speed distributions, the luminescence decay curves, and the Stern-Volmer graphs. The software named "SternVolmer" is written for the FreeBASIC compiler and can be applied to dynamic systems where luminescent molecules, during their excited state lifetimes, are able to collide with quenching molecules (collisional quenching). The good agreement found between the simulations and the expected results shows that this software can be used as an effective teaching aid for the study of luminescence and kinetic decay of excited states.

Simulação de sinais de RMN através das equações de Bloch

The aim of this paper was to present a simple and fast way of simulating Nuclear Magnetic Resonance signals using the Bloch equations. These phenomenological equations describe the classical behavior of macroscopic magnetization and are easily simulated using rotation matrices. Many NMR pulse sequences can be simulated with this formalism, allowing a quantitative description of the influence of many experimental parameters. Finally, the paper presents simulations of conventional sequences such as Single Pulse, Inversion Recovery, Spin Echo and CPMG.