Determinação de pesticidas organofosforados em água usando microextração em fase sólida e CGAR-EM

Solid-phase microextraction (SPME) has been applied to direct extraction of 11 organophosphorus pesticides in water using a 100 mm fiber polydimethylsiloxane. The method was evaluated with respect time of exposure, detection limits (LODs), linearity and precision. The detection limits (S/N = 3) depend of each pesticide and varie about ng/L levels. The linearity was satisfactory with coefficients of correlation usually greater than 0.993. The precision of the method was determined by extraction from 4.0 mg/L aqueous standard with coefficients of variation between 5.7 to 17.2%.

Determinação direta de selênio em água de coco e em leite de coco utilizando espectrometria de absorção atômica com atomização eletrotérmica em forno de grafite

Selenium is both essential and toxic to man and animals, depending on the concentration and the ingested form. Most fruits and vegetables are poor sources of selenium, but coconut can be a good selenium source. Samples were suspended (1 + 4 v/v) in a mixture of tertiary amines soluble in water (10% v/v CFA-C). This simple sample treatment avoided contamination and decreased the analysis time. The standard additions method was adopted for quantification. The action of the autosampler was improved by the presence of the amines mixture in the suspension. A Varian model AA-800 atomic absorption spectrometer equipped with a graphite furnace and a GTA 100 autosampler was used for selenium determination in coconut water and coconut milk. Background correction was performed by means of the Zeeman effect. Pyrolytically coated graphite tubes were employed. Using Pd as chemical modifier, the pyrolysis and the atomization temperatures were set at 1400 and 2200ºC, respectively. For six samples, the selenium concentration in coconut water varied from 6.5 to 21.0 mug L-1 and in coconut milk from 24.2 to 25.1 mug L-1. The accuracy of the proposed method was evaluated by an addition-recovery experiment and all recovered values are in the 99.5-102.3% range. The main advantage of the proposed method is that it can be directly applied without sample decomposition.

Relações da atividade agropecuária com parâmetros físicos químicos da água

Water Quality Index (WQI) was used during summer and winter of 1994 and 1995 in the final section of Onça and Feijão streams, downstream Broa Reservoir (São Carlos/SP) to evaluate agricultural and catlleman effects. In Onça stream water quality was "acceptable" in winter and "inappropriate to conventional treatment" in the summer. In Feijão stream the water had an "excellent" quality in winter and "good" in the summer. A MANOVA (Multivariate Analysis of Variance) has used to discriminate seasons and streams. Correlation (p<0,05) among the variables was tested. Water temperature, turbidity, pH and fecal bacteria are highly correlated and can be one of the factors that cause WQI change by seasons.

Catálise de transferência de fase

Since its discovery, phase transfer catalysis (PTC) has grown considerably and nowadays is one of the most versatile preparative methods. The search for new catalysts, their use in PTC asymmetric synthesis and the attempts to understand their mechanistic role are modern and exciting topics of investigation. A review on main achievements in the last two decades is presented.

Extração em fase sólida (SPE) e micro extração em fase sólida (SPME) de piretróides em água

The pyrethroids bifenthrin, permethrin, cypermethrin and deltamethrin were extracted by solid phase extraction (SPE) and solid phase microextraction (SPME). The analysis were performed on a gas chromatograph with electron capture detection (GC-ECD). Octadecil Silano-C18, Florisil and Silica stationary phases were studied for SPE. Better results were obtained for Florisil which gave recoveries from 80% to 108%. Pyrethroids extraction by SPME showed a linear response and a detection limit of 10 pg ml-1. Although the data showed that the two extraction methods were able to isolate the pesticide residues from water samples, the best results were obtained by using SPME which is more sensitive, faster, cheeper, being a more useful technique for the analysis of pyrethroids in drinking water.

Comparação entre injeção na coluna ("on-column") e headspace dinâmico na determinação de benzeno, tolueno e xilenos (BTX) em amostras de água

The analysis of water samples containing volatile organic compounds has become an important task in analytical chemistry. Gas chromatography has been widely used for the analysis of volatile organic compounds in water. The headspace analysis shows as a principal characteristic the possibility of determination of the volatile components in drinking water. Benzene, Toluene and Xylene (BTX) are important compounds usually present in drinking water, from contamination by petroleum derivatives. Since they are toxic compounds even when present in low concentration levels, their determination is important in order to define the quality of the water. The sampling technique using headspace, coupled with gas chromatography as the separation method, showed to be suitable for BTX analysis in several samples at the mug/L (ppb) level.

Nitração aromática: substituição eletrofílica ou reação com transferência de elétrons?

Aromatic nitration is one of the most relevant class of reactions in organic chemistry. It has been intensively studied by both experimental, including works in the condensed as well as in the gas phase, and theoretical procedures. However, the published results do not seem to converge to an unique mechanism. Electrophilic substitution and electron transfer, in an exclusive way, are both proposed as the main mechanism for the reaction. We review these proposals and discuss the most recent findings.

Deposição eletrolítica catódica e anódica simultâneas para minimizar interferências de cobre e chumbo na determinação espectrofotométrica de cádmio em água e alimentos via reação com Verde de Malaquita e iodeto

Simultaneous electrolytic deposition is proposed for minimization of Cu2+ and Pb2+ interferences on automated determination of Cd2+ by the Malachite Green-iodide reaction. During electrolysis of sample in a cell with two Pt electrodes and a medium adjusted to 5% (v/v) HNO3 + 0.1% (v/v) H2SO4 + 0.5 mol L-1 NaCl, Cu2+ is deposited as Cu on the cathode, Pb2+ is deposited as PbO2 on the anode while Cd2+ is kept in solution. With 60 s electrolysis time and 0.25 A current, Pb2+ and Cu2+ levels up to 50 and 250 mg L-1 respectively, can be tolerated without interference. With on-line extraction of Cd2+ in anionic resin minicolumn, calibration graph in the 5.00 - 50.0 µg Cd L-1 range is obtained, corresponding to twenty measurements per hour, 0.7 mg Malachite Green and 500 mg KI and 5 mL sample consumed per determination. Results of the determination of Cd in certified reference materials, vegetables and tap water were in agreement with certified values and with those obtained by GFAAS at 95% confidence level. The detection limit is 0.23 µg Cd L-1 and the RSD for typical samples containing 13.0 µg Cd L-1 was 3.85 % (n= 12).

Transferência de elétrons em sistemas inorgânicos de valência mista

This article reports on some basic and conceptual principles concerning electron transfer (ET) and/or intervalence transfer (IT) phenomena in inorganic mixed-valence systems.

Utilização de índices r e R obtidos de programas interlaboratoriais para o controle de precisão de método analítico: Determinação de água por Karl Fischer

Values of repeatability (r) and reproducibility (R) are parameters of an analytical method. They are related to the maximum difference between two results of analysis (permissible range) and can be obtained by interlaboratorial comparisons. They represent great importance for the quality control of the results and decisions about the fitness-for-purpose of the method. Water determination in fuel oil samples were performed by 16 laboratories, using the Karl Fischer reaction, during the period from June 1997 to December 1999. Values of r and R were presented. Discussion is made in terms of the main factors that would be contribution to analytical method variabilities and uncertainties of final results.

Utilização de zeólita preparada a partir de cinza residuária de carvão como adsorvedor de metais em água

Coal ashes produced in coal-fired power plant could be converted into zeolites and can be used as low-cost adsorbents for the treatment of effluents contaminated with high levels of toxic metals. The capacity of synthetic zeolites for the removal of cadmium, zinc and copper ions from aqueous solutions has been investigated under different operating conditions. Zeolite from bottom chimney showed higher removal efficiency for metals ions than zeolite from feed hopper and mixing mill. The results indicated that the treated bottom ash could be applied in environmental technology as an immobilizer of pollutants.

Estudo do coeficiente de partição octanol-água de bifenilas policloradas (PCBs) utilizando parâmetros topológicos

A model based on chemical structure was developed for the accurate prediction of octanol/water partition coefficient (K OW) of polychlorinated biphenyls (PCBs), which are molecules of environmental interest. Partial least squares (PLS) was used to build the regression model. Topological indices were used as molecular descriptors. Variable selection was performed by Hierarchical Cluster Analysis (HCA). In the modeling process, the experimental K OW measured for 30 PCBs by thin-layer chromatography - retention time (TLC-RT) has been used. The developed model (Q² = 0,990 and r² = 0,994) was used to estimate the log K OW values for the 179 PCB congeners whose K OW data have not yet been measured by TLC-RT method. The results showed that topological indices can be very useful to predict the K OW.

Transferência de energia entre corantes catiônicos em sistemas homogêneos

In this work, the energy transfer by dipole-dipole interaction between cationic dyes in n-alcohols (methanol, ethanol, 1-propanol and 1-butanol) is studied by time resolved and steady state fluorescence measurements. The critical radii of energy transfer were determined by three independent methods; the spectral overlap, fluorescence decay profiles, and relative intensity measurements. In all solvents, R0 values of the dye pairs obtained from spectral overlap were between 40 to 90 Å. Steady state and time resolved fluorescence measurements resulted in values of R0 in the range of 50 - 80 Å, with good correlation of values.

Transferència tecnològica

Es pot fer una anàlisi sobre les diferències entre les universitats que transfereixen molt coneixement i les nostres. També, es poden comparar les condicions socioeconòmiques, en relació a la creació d'empreses, i els 'clients' de les universitats, en relació als contractes de transferència. Aquesta informació ens pot ajudar a decidir què podem fer per millorar aquests pobres resultats

Les Unitats de transferència i comercialització de tecnologia universitària

Aquest article presenta els resultats de l’anàlisi de cinquanta-dues unitats de transferència de tecnologia generada al sector públic. L’objectiu de l’anàlisi era aportar informació i coneixement adreçats a facilitar en el nostre entorn el disseny d’unitats de comercialització de patents i spin-offs per part de les autoritats universitàries i de les agències d’innovació. El projecte ha estat finançat pel Centre d'Innovació i Desenvolupament Empresarial (CIDEM) de la Generalitat de Catalunya