178,627 research outputs found
Strong complexation of lead(II) by fulvic substances under environmental relevant conditions
No full textBecause of the high concern of lead(II) in the environment, its speciation had been largely investigated in the past years. Different ligands of lead(II) can be present in natural waters ranging from inorganic anions, often at high concentration (chloride, carbonate) with side reaction coefficient around 30
(1), to very strong complexing sites present in NOM (natural organic matter). Side reaction coefficients of lead(II) slightly higher than those for inorganic ligands have been reported for humic substances (2). These sites are at low concentration but display a high complexation strength. Consequently they will be the first to take up the metal, while the weaker sites contribute to complexation only at higher total metal concentrations.
Stronger lead(II) ligands have been detected in natural waters using a method with detection window much higher than the usual ones, based on the partition of the metal ion on complexing resins (3). Side reaction coefficients as high as about 106 were evaluated in natural waters. A similar method (4) was here used to determine the complexing properties for lead(II) of a fulvic acid extracted from a sediment (FA), at low concentration, 10-500 nM. It is based on the sorption of lead(II) on the ionexchange
complexing resins Chelex 100 and Amberlite CG 50.
In the FA at pH around neutrality strong complexation sites of lead(II) were detected, with concentration 2 10-3 mmol g-1-0.04 mmol g-1 similar to that determined by other methods (2), but conditional complexation constant as high as log K=13-15, much higher than that previously obtained, but similar to those found in natural waters (3). These sites heavily determine the lead(II) complexation since the metal in natural waters is present at nM
level. A large influence of the solution pH on the complexing properties of the strong ligands has been found. On the other hand, using an ion exchange resin (Dowex 50W-X8) with lower detection window, lead(II) ligands with lower side reaction coefficient, near to that determined in previous investigations (2), were detected.
(1) D. Turner, M. Whitfield, A.G. Dickson, Geochim. Cosmochim. Acta, 45 (1981) 855-874.
(2) M. Filella, R.M. Town, Sci. Tot. Environ. 300 (2002) 143–154.
(3) G. Alberti, R. Biesuz, M. Pesavento, Anal. Sci. 24 (2008) 1605-1611.
(4) M. Pesavento, A. Profumo, R. Biesuz, G. Alberti, Solv. Extr.Ion Exch. 26 (2008) 301-320.
(5) R. Biesuz, G. Alberti, M. Pesavento, J. Sol. Chem. 37 (2008) 527–541
A portable, disposable, and low-cost optode for sulphide and thiol detection
No full textIn this study, a portable, disposable, and low-cost ionophore-based optical sensor is presented for the monitoring of sulphides and thiols. This sensor was obtained by fixing a classical dye, 5,5 '-dithiobis(2-nitrobenzoic acid) (Ellman's reagent, ELL), on an unusual solid support. Indeed, we decided to anchor the dye on the commercial paper sheet known as the "Colour Catcher (R)" (herein, named under the acronym CC), commonly used in the washing machine to prevent colour run problems. The device obtained can be regarded as an optical sensor since the indicator dye fixed on the solid material changes its spectral properties (colour and hence the UV-vis spectrum) upon contact with the analyte. The relationship between the analyte content and changes in the UV-vis spectrum of the sensor has been provided using partial least squares regression (PLS)
Inexpensive Alizarin Red S-based optical device for the simultaneous detection of Fe(III) and Al(III)
No full textThis work presents a simple, fast, disposable and low-cost colorimetric sensor for the simultaneous detection of Fe(III) and Al(III). It is obtained by fixing a classical dye, Alizarin Red S, on an inert solid support, i.e., a product of the washing powder market known as “Colour Catcher®” (here named under the acronym CC) generally used in the washing machine to prevent colour run problems. The device so obtained is called Aliz-CC@. Fe(III) and Al(III) interaction with the Alizarin Red S-based sensor, generates a change in the adsorption spectra of the fixed dye, allowing to highlight a naked-eye colour change. The relationship between the Fe(III) and Al(III) content and the colour change profiles of the sensor, is provided by using Partial Least Squares regression (PLS)
Gold and silver nanoparticle-based colorimetric sensors: New trends and applications
No full textGold and Silver nanoparticles (AuNPs and AgNPs) are perfect platforms for developing sensing colorimetric devices thanks to their high surface to volume ratio and distinctive optical properties, particularly sensitive to changes in the surrounding environment. These characteristics ensure high sensitivity in colorimetric devices. Au and Ag nanoparticles can be capped with suitable molecules that can act as specific analyte receptors, so highly selective sensors can be obtained. This review aims to highlight the principal strategies developed during the last decade concerning the preparation of Au and Ag nanoparticle-based colorimetric sensors, with particular attention to environmental and health monitoring applications
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Silver nanoparticles from orange peel extract: Colorimetric detection of Pb2+ and Cd2+ ions with a chemometric approach
No full textGreen silver nanoparticles (AgNPs@OPE) were obtained by using orange (citrus sinensis) peel water extract (OPE) that acts as a reducing and capping agent. This procedure permits the valorisation of waste as orange peel, and lowers the environmental impact of the process, with respect to the conventional synthetic procedure. The OPE extract reduced Ag(I) to Ag(0) in alkaline conditions, and stabilised the produced nanoparticles as a capping agent. The AgNPs@OPE were deeply characterized by UV–Vis spectroscopy, FT-IR, SEM analysis and DLS analysis and successively used as colorimetric sensors for different metals in aqueous solution. The colourimetric assay showed that AgNPs@OPE were able to detect Pb2+ and Cd2+, as demonstrated by the splits of surface plasmon resonance (SPR) band accompanied by the formation of a second new band; these spectral modification resulted in a colour change, from pristine nanoparticles’ yellow to brown, due to the aggregation process. For the quantification of each of the two target cations, a calibration was performed by using the univariate linear regression, within the linearity ranges, exploiting the absorbance ratio between the main SPR band and the new band relative to the aggregate formation. Then a multivariate approach was followed to perform both Cd2+ and Pb2+ quantification by means of Partial Least Square regression (PLS) and target cations distinction by Linear Discriminant Analysis (LDA) applied on Principal Components Analysis (PCA) outputs, in both cases using the entire UV–Vis spectra (350–800 nm) as input data. Finally, the ability to quantify and distinguish between Cd2+ and Pb2+ was tested in tap water samples spiked with the two cations in order to confirm the application of the AgNPs@OPE as selective sensor in real samples
"Closing the R&D Gap, Evaluating the Sources of R&D Spending"
No full textBoth spending and tax policies have been implemented in the United States with the goal of stimulating private sector research and development (R&D). Karier questions whether current R&D policy, especially the research and experimentation tax credit, can contribute to closing the gap between nondefense expenditures on R&D in the United States and such expenditures in other countries, such as Japan and Germany. He also explores possible changes to our current R&D policy to make it more effective.
On the gasification of biomass: Data analysis and regressions
No full textThe use of solid wastes as a way to produce energy and chemicals is one of the frontiers in chemistry. One of these methods is the biomass gasification. In this thermal treatment the biomass is heated in a partially oxidizing environment using different process conditions.
The variability of both biomass composition and process conditions can lead the thermal treatment to several different results. In order to find a methodology for the classification of all the involved data a dataset containing biomass characterization, gasification process conditions and obtained syngas properties have been gathered from the literature.
This dataset has been analysed through multivariate analysis. Principal component analysis (PCA) and a partial least square analysis (PLS) have been performed. Several correlations among different biomass and their gasification products have been found among input parameters, such as biomass properties and process conditions, and output variables like products composition and properties
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