Development of a flow method for the determination of phosphate in estuarine and freshwaters - Comparison of flow cells in spectrophotometric sequential injection analysis

A sequential injection system with dual analytical line was developed and applied in the comparison of two different detection systems viz; a conventional spectrophotometer with a commercial flow cell, and a multi-reflective flow cell coupled with a photometric detector under the same experimental conditions. The study was based on the spectrophotometric determination of phosphate using the molybdenum-blue chemistry. The two alternative flow cells were compared in terms of their response to variation of sample salinity, susceptibility to interferences and to refractive index changes. The developed method was applied to the determination of phosphate in natural waters (estuarine, river, well and ground waters). The achieved detection limit (0.007 mu M PO43-) is consistent with the requirement of the target water samples, and a wide quantification range (0.024-9.5 mu M) was achieved using both detection systems.info:eu-repo/semantics/submittedVersioninfo:eu-repo/semantics/acceptedVersio

Impact of iron amendment on soil bacterial abundance and diversity

info:eu-repo/semantics/publishedVersio

Use of a sequential injection system to monitor the efficiency of a constructed wetland

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A robust flow-based system for the spectrophotometric determination of Cr(VI) in recreational waters

A flow-based method for the spectrophotometric determination of chromium (VI) in recreational waters with different salinities was developed. Chromium can occur in the environment in different oxidation states with different related physiological properties. With regard to chromium, the speciation is particularly important, as the hexavalent chromium is considered to be carcinogenic. To achieve that purpose, the use of the diphenylcarbazide (DPC) selective colored reaction with the hexavalent chromium was the chosen strategy. The main objective was to develop a direct and simple spectrophotometric method that could cope with the analysis of different types of environmental waters, within different salinity ranges (fresh to marine waters). The potential interference of metal ions, that can usually be present in environmental waters, was assessed and no significant interferences were observed (<10%). For a complete Cr(VI) determination (three replicas) cycle, the corresponding reagents consumption was 75 µg of DPC, 9 mg of ethanol and 54 mg of sulfuric acid. Each cycle takes about 5 min, including the system clean-up. The limit of detection was 6.9 and 12.2 µg L−1 for waters with low and high salt content, respectively. The method was applied for the quantification of chromium (VI) in both fresh and marine water, and the results were in agreement with the reference procedure.info:eu-repo/semantics/publishedVersio

The effects of meson mixing on dilepton spectra

The effect of scalar and vector meson mixing on the dilepton radiation from hot and dense hadronic matter is estimated in different isospin channels. In particular, we study the effect of $\sigma$-$\omega$ and $\rho-a_0$ mixing and calculate the corresponding rates. Effects are found to be significant compared to standard $\pi$-$\pi$ and $K$-${\bar K}$ annihilations. While the mixing in the isoscalar channel mostly gives a contribution in the invariant mass range between the two-pion threshold and the $\omega$ peak, the isovector channel mixing induces an additional peak just below that of the $\phi$. Experimentally, the dilepton signals from $\rho$-$a_0$ mixing seem to be more tractable than those from $\sigma$-$\omega$ mixing.Comment: 10 pages, 9 figure

Development of a sequential injection system for the determination of nitrite and nitrate in waters with different salinity: Application to estuaries in NW Portugal

In this work, a sequential injection methodology for monitoring nitrite and nitrate in estuarine waters without any previous treatment is described. The developed system was applied to the measurement of nitrite and nitrate in estuarine waters of three rivers in the NW Portugal, allowing an automatic, fast (ca 60 h 1) and precise method (relative standard deviation lower than 2%). The procedure was based on the reaction between nitrite, sulfanilamide and N-(1-naphthyl)-ethylenediamine dihydrochloride (N1NED), whereas the determination of nitrate resulted from its reduction to nitrite, using an in-line cadmium column, followed by the same reaction. The samples were collected in three locations for each river (Douro, C avado and Ave) covering the lower, middle and upper section of the estuaries. Despite the presence of a salinity gradient, this parameter showed no interference in the accuracy of the determinations. The results obtained for the described method for nitrite were statistically comparable to those obtained by the reference procedure. For the determination of nitrate, recovery tests confirmed that the sequential injection methodology provided good quality results.info:eu-repo/semantics/publishedVersio

Geometric K-Homology of Flat D-Branes

We use the Baum-Douglas construction of K-homology to explicitly describe various aspects of D-branes in Type II superstring theory in the absence of background supergravity form fields. We rigorously derive various stability criteria for states of D-branes and show how standard bound state constructions are naturally realized directly in terms of topological K-cycles. We formulate the mechanism of flux stabilization in terms of the K-homology of non-trivial fibre bundles. Along the way we derive a number of new mathematical results in topological K-homology of independent interest.Comment: 45 pages; v2: References added; v3: Some substantial revision and corrections, main results unchanged but presentation improved, references added; to be published in Communications in Mathematical Physic