Multiresidue analysis and evaluation of the matrix effect on 20 pesticides in Brazilian maize (Zea mays L.) flour.

Maize consists of a cereal widely used in the preparation of different food products. Brazil is one of the world's largest maize producers. Several types of pesticides have been applied in maize crop, which can lead to the contamination of the derived products. The present work aims at the validation of multiresidue method to analyze the matrix effect and level of pesticides in maize flour. Twenty residues were investigated in samples commercialized in the state of Ceará, Brazil. The method was satisfactorily validated, according to parameters recommended by European Union. About 55% of the pesticides had an intense negative matrix effect. Multiresidue analyzes showed the presence of traces of fenitrotion in 20% of maize flour samples. Detected levels were below maximum residue limits recommended for maize. The results indicate that maize products need continuous monitoring to ensure food security.

Mutual Neutralization of O

We have measured total absolute cross sections for the mutual neutralization (MN) of O^{-} with O^{+} and N^{+}. A fine resolution (of about 50 meV) in the kinetic energy spectra of the product neutral atoms allows unique identification of the atomic states participating in the mutual neutralization process. Cross sections and branching ratios have also been calculated down to 1 meV center-of-mass collision energy for these two systems, with a multichannel Landau-Zener model and an asymptotic method for the ionic-covalent coupling matrix elements. The importance of two-electron processes in one-electron transfer is demonstrated by the dominant contribution of a core-excited configuration of the nitrogen atom in N^{+}+O^{-} collisions. This effect is partially accounted for by introducing configuration mixing in the evaluation of coupling matrix elements.

Storing keV negative ions for an hour: the lifetime of the metastable

We use a novel electrostatic ion storage ring to measure the radiative lifetime of the upper level in the 3p^{5} ^{2}P_{1/2}^{o}→3p^{5} ^{2}P_{3/2}^{o} spontaneous radiative decay in ^{32}S^{-} to be 503±54 sec. This is by orders of magnitude the longest lifetime ever measured in a negatively charged ion. Cryogenic cooling of the storage ring gives a residual-gas pressure of a few times 10^{-14} mbar at 13 K and storage of 10 keV sulfur anions for more than an hour. Our experimental results differ by 1.3σ from the only available theoretical prediction [P. Andersson et al., Phys. Rev. A 73, 032705 (2006)].

Experimental evidence of twin fast metastable H(2(2)S) atoms from dissociation of cold H2 induced by electrons.

We report the direct detection of two metastable H(2^{2}S) atoms coming from the dissociation of a single cold H(2) molecule, in coincidence measurements. The molecular dissociation was induced by electron impact in order to avoid limitations by the selection rules governing radiative transitions. Two detectors, placed close to the collision center, measure the neutral metastable H(2(2)S) through a localized quenching process, which mixes the H(2^{2}S) state with the H(2^{2}P), leading to a Lyman-α detection. Our data show the accomplishment of a coincidence measurement which proves for the first time the existence of the H(2(2)S)-H(2(2)S) dissociation channel.

Anthraquinone-2,6-disulfonate (AQDS) as a catalyst to enhance the reductive decolourisation of the azo dyes Reactive Red 2 and Congo Red under anaerobic conditions.

In this study, we assessed the catalytic effect of anthraquinone-2,6-disulfonate (AQDS) to enhance the reductive decolourisation of the azo dyes Reactive Red 2 and Congo Red in batch and continuous-flow experiments. While testing the anaerobic sludge 1 in assays free of AQDS, the highest values for the first-order kinetic constant (k1) were found with co-substrates formate and glucose. In the assays that contained 50 microM of AQDS, the k1 values increased with all co-substrates tested, increasing by 3.5-fold when ethanol was the electron donor. The upflow anaerobic sludge blanket (UASB) reactors R1 (AQDS-free) and R2 (AQDS-supplemented) reached excellent decolourisation efficiencies (higher than 90%) even for the high Congo Red concentration tested (1.2 mM). However, electron donor depletion in the influent drastically decreased the colour removal capacity in both bioreactors. Reactor R2 presented higher stability and decolourisation efficiency compared to R1, indicating that the addition of a redox mediator can be valuable for treating dye-coloured wastewaters.

New approach for petroleum hydrocarbon degradation using bacterial spores entrapped in chitosan beads.

Spores of Bacillus subtilis LAMI008 were entrapped in 3-mm chitosan beads and cross-linked with 0.3% glutaraldehyde for n-hexadecane biodegradation and biosurfactant recovery. When exposed to nutrients, the spores generated vegetative cells without morphological alterations as revealed by atomic force microscopy. The entrapped cells degraded almost 100% of 1% of n-hexadecane in medium supplemented with 1% glucose and produce biosurfactant within 48 h, as well as free cells. The number of viable cells inside the beads was maintained throughout the n-hexadecane degradation process and the released biosurfactant was not used as a carbon source. Entrapment of bacterial spores in chitosan beads overcomes problems with stability, storage, and long term cell viability encountered with vegetative cells. This approach can potentially be utilized for biodegradation of complex compounds by entrapping spores of different species of bacteria.

Qualitative and quantitative high-performance liquid chromatographic analysis of aldehydes in Brazilian sugar cane spirits and other distilled alcoholic beverages.

A study is presented on the high-performance liquid chromatographic analysis of eighteen aldehydes in Brazilian sugar cane spirits and other international brandies. The aldehydes were separated by reversed-phase high-performance liquid chromatography as 2,4-dinitrophenylhydrazones (DNPHs). A very good chromatographic separation was achieved for eighteen different aldehyde-DNPHs. The proposed methodology is quite simple and not very time-consuming. Ten aldehydes were identified in 75 beverages and quantified using the external standard method with UV detection at 365 nm. A detailed knowledge of the aldehyde content should significantly contribute to improving the quality control of distilled spirits.