The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Carlos Bendicho - One of the best experts on this subject based on the ideXlab platform.
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Miniaturized and green method for determination of chemical oxygen demand using UV-induced oxidation with hydrogen peroxide and single drop microextraction
Mikrochimica Acta, 2013Co-Authors: Jeyran Akhoundzadeh, Marta Costas, Isela Lavilla, Mahmoud Chamsaz, Carlos BendichoAbstract:We report on a green method for the determination of low levels of chemical oxygen demand. It is based on the combination of (a) UV-induced oxidation with hydrogen peroxide, (b) headspace single-drop microextraction with in-drop precipitation, and (c) micro-Turbidimetry. The generation of CO2 after photolytic oxidation followed by its sequestration onto a microdrop of barium hydroxide gives rise to a precipitate of barium carbonate which is quantified by Turbidimetry. UV-light induced oxidation was studied in the absence and presence of H2O2, ultrasound, and ferrous ion. Determinations of chemical oxygen demand were performed using potassium hydrogen phthalate as a model compound. The optimized method gives a calibration curve that is linear between 3.4 and 20 mg L−1 oxygen. The detection limit was 1.2 mg L−1 of oxygen, and the repeatability (as relative standard deviation) was around 5 %. The method was successfully applied to the determination of chemical oxygen demand in different natural waters and a synthetic wastewater.
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microvolume Turbidimetry for rapid and sensitive determination of the acid labile sulfide fraction in waters after headspace single drop microextraction with in situ generation of volatile hydrogen sulfide
Analytica Chimica Acta, 2009Co-Authors: Isela Lavilla, Marta Costas, Francisco Penapereira, Sandra Gil, Carlos BendichoAbstract:Abstract In this work, we demonstrate the feasibility of applying headspace single-drop microextraction with in-drop precipitation for the quantitative determination of the acid labile sulfide fraction (H2S, HS−, and S2− (free sulfide), amorphous FeS and some metal sulfide complexes–clusters as ZnS) in aqueous samples by microvolume Turbidimetry. The methodology lies in the in situ hydrogen sulfide generation and subsequent sequestration into an alkaline microdrop containing ZnO22− and exposed to the headspace above the stirred aqueous sample. The ZnS formed in the drop was then determined by microvolume Turbidimetry. The optimum experimental conditions of the proposed method were: 2 μL of a microdrop containing 750 mg L−1 Zn(II) in 1 mol L−1 NaOH exposed to the headspace of a 20-mL aqueous sample stirred at 1600 rpm during 80 s after derivatization with 1 mL of 6 mol L−1 HCl. An enrichment factor of 1710 was achieved in only 80 s. The calibration graph was linear in the range of 5–100 μg L−1 with a detection limit of 0.5 μg L−1. The repeatability, expressed as relative standard deviation, was 5.8% (N = 9). Finally, the proposed methodology was successfully applied to the determination of the acid labile sulfide fraction in different natural water samples.
Isela Lavilla - One of the best experts on this subject based on the ideXlab platform.
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Miniaturized and green method for determination of chemical oxygen demand using UV-induced oxidation with hydrogen peroxide and single drop microextraction
Mikrochimica Acta, 2013Co-Authors: Jeyran Akhoundzadeh, Marta Costas, Isela Lavilla, Mahmoud Chamsaz, Carlos BendichoAbstract:We report on a green method for the determination of low levels of chemical oxygen demand. It is based on the combination of (a) UV-induced oxidation with hydrogen peroxide, (b) headspace single-drop microextraction with in-drop precipitation, and (c) micro-Turbidimetry. The generation of CO2 after photolytic oxidation followed by its sequestration onto a microdrop of barium hydroxide gives rise to a precipitate of barium carbonate which is quantified by Turbidimetry. UV-light induced oxidation was studied in the absence and presence of H2O2, ultrasound, and ferrous ion. Determinations of chemical oxygen demand were performed using potassium hydrogen phthalate as a model compound. The optimized method gives a calibration curve that is linear between 3.4 and 20 mg L−1 oxygen. The detection limit was 1.2 mg L−1 of oxygen, and the repeatability (as relative standard deviation) was around 5 %. The method was successfully applied to the determination of chemical oxygen demand in different natural waters and a synthetic wastewater.
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microvolume Turbidimetry for rapid and sensitive determination of the acid labile sulfide fraction in waters after headspace single drop microextraction with in situ generation of volatile hydrogen sulfide
Analytica Chimica Acta, 2009Co-Authors: Isela Lavilla, Marta Costas, Francisco Penapereira, Sandra Gil, Carlos BendichoAbstract:Abstract In this work, we demonstrate the feasibility of applying headspace single-drop microextraction with in-drop precipitation for the quantitative determination of the acid labile sulfide fraction (H2S, HS−, and S2− (free sulfide), amorphous FeS and some metal sulfide complexes–clusters as ZnS) in aqueous samples by microvolume Turbidimetry. The methodology lies in the in situ hydrogen sulfide generation and subsequent sequestration into an alkaline microdrop containing ZnO22− and exposed to the headspace above the stirred aqueous sample. The ZnS formed in the drop was then determined by microvolume Turbidimetry. The optimum experimental conditions of the proposed method were: 2 μL of a microdrop containing 750 mg L−1 Zn(II) in 1 mol L−1 NaOH exposed to the headspace of a 20-mL aqueous sample stirred at 1600 rpm during 80 s after derivatization with 1 mL of 6 mol L−1 HCl. An enrichment factor of 1710 was achieved in only 80 s. The calibration graph was linear in the range of 5–100 μg L−1 with a detection limit of 0.5 μg L−1. The repeatability, expressed as relative standard deviation, was 5.8% (N = 9). Finally, the proposed methodology was successfully applied to the determination of the acid labile sulfide fraction in different natural water samples.
Michel Cournil - One of the best experts on this subject based on the ideXlab platform.
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On-line determination of aggregate size and morphology in suspensions
2003Co-Authors: Michel Cournil, Frédéric Gruy, Patrick CugnietAbstract:Information about the aggregation state of fine particles is an important element for process control, product quality monitoring and fundamental understanding in many cases of industrial slurries. When aggregates are small or fragile objects, their withdrawal is difficult and off-line characterization may be a source of error. This work deals with the application of different in line methods to the characterization of silica aggregate size and morphology. These methods are based on Turbidimetry. One of them consists of the analysis of the turbidity fluctuations and is operated on a commercial instrument. The other one uses the aggregate settling velocity which is determined by Turbidimetry too, however with a home-made apparatus. This work gives us the opportunity to define morphological models for small aggregates and to calculate their drag coefficient. Thanks to these models, the aggregate morphological characteristics and the number of their constituting particles can be derived from the experimental results. Agreement between the different methods is examined and discussed.
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Size analysis of fine particle suspensions by spectral Turbidimetry: potential and limits
Powder Technology, 1997Co-Authors: George Martin Crawley, Michel Cournil, D. Di BenedettoAbstract:In this paper, the potential and limits of Turbidimetry as a particle sizing method are discussed with respect to several aspects, theoretical and experimental. A complete experimental set-up consisting of a spectrophotometer and different types of in situ sensors, a data acquisition system, and a calculation program are described. The possible uses of this method for on-line measurements are discussed, particularly in the field of crystallization and powder technology. Two examples of its application are briefly presented.
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Agglomeration of alumina powders: A turbidimetric study
Chemical Engineering and Technology, 1995Co-Authors: Jean Claude Masy, Michel Cournil, Michel LanceAbstract:Turbidimetry has proved to be an efficient method for the quantitative study of powder agglomeration for particle sizes in the region of 1 m. This work presents a new application of the technique for the agglomeration of -alumina in water and in n-heptane. The method of determining the kinetic parameters of agglomeration from the initial time-evolution of turbidity is explained. Turbulent flow in the reactor has also been characterised by laser anemometry. From the turbulence intensity, the number of collisions per unit time is calculated and the agglomeration rate can therefore be determined. Good agreement is found between the values obtained respectively from turbidimetric and hydrodynamic measurements. Addition of KOH modifies the zeta potential of alumina in water and influences the agglomeration kinetics. This can also be quantitatively characterised by Turbidimetry. The experimental results obtained for alumina particles of diameter 0.3 m and 1 m are interpreted according to the DLVO model of interaction between particles.
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Secondary nucleation of potassium dihydrogen phosphate (KDP): Interest of a turbidimetric study
Powder Technology, 1992Co-Authors: Philippe Triboulet, Michel Cournil, George Martin CrawleyAbstract:Secondary nucleation of potassium dihydrogen phosphate (KDP) is studied from electrical conductometry and Turbidimetry experiments. Different possible mechanisms are investigated: initial breeding is observed even in the absence of stirring; production of nuclei by collisions with the reactor walls (contact nucleation) is studied in a liquid medium in which KDP is not soluble so that effects other than hydrodynamical/mechanical phenomena are eliminated. Similarities between secondary and heterogenous nucleation could indicate the existence of a mechanism of surface nucleation in addition to the other two effects. Turbidimetry is particularly useful for the quantitative study of the dynamics of secondary nucleation: in this work, it is applied to the study of the inhibition of nuclei production by dissolved aluminium ions. An estimation of the size of the secondary nuclei is calculated from turbidity data.
Kh.u. Usmanov - One of the best experts on this subject based on the ideXlab platform.
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Determination of solubility parameters of chlorinated poly(vinyl chloride) by Turbidimetry and viscosimetry
Journal of Polymer Science Part C: Polymer Symposia, 2007Co-Authors: R.s. Tillaev, M. Khasankhanova, S.a. Tashmukhamedov, Kh.u. UsmanovAbstract:The product of chlorination of poly(vinyl chloride), perchlorovinyl (PerCV), dissolves in most organic solvents, a fact explained by the weakening of intermolecular interaction by irregular disposition of chlorine atoms along the chain. For evaluation of the changes in these forces, solubility parameters were determined by the method of Turbidimetry and viscosimetry proposed by Suh, Clark, and Mangarai. For Turbidimetry 15 solvents of differing chemical nature and 2 nonsolvents were used: hexane (low solubility parameter) and methanol (high solubility parameter). Values of the intrinsic viscosity and Huggins constants were obtained from viscometric data. Consideration of the results in terms of the Flory-Huggins theory gave a value of 9.30(cal/cm3)1/2 for the solubility parameter of PerCV.
R J Haynes - One of the best experts on this subject based on the ideXlab platform.
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effect of sample pretreatment on aggregate stability measured by wet sieving or Turbidimetry on soils of different cropping history
European Journal of Soil Science, 1993Co-Authors: R J HaynesAbstract:SUMMARY The effects of cropping history (pasture or arable) and sample pretreatment (field-moist, air-dried or air-dried and then tension or vacuum rewetted) on aggregate stability as measured by wet sieving or Turbidimetry were compared. When field-moist samples were used there was a tendency for aggregate stability, as measured by wet sieving, to decline with increasing time under arable cropping (i.e. decreasing soil organic matter content). Air-drying samples caused a pronounced decline in stability of soils from under arable management and as a consequence there was a marked decline in stability with increasing time under arable. Use of tension or vacuum rewetted samples resulted in high values of stability which were unaffected by cropping history. For Turbidimetry, there was a marked decline in measured stability with increasing time under arable cropping when field-moist samples were used. Air-drying caused an increase in measured stability that was relatively greater for the less stable samples. In comparison with air-dried samples, tension and vacuum rewetting caused a decrease in stability values for relatively unstable soils. It is suggested that, upon air-drying (and contraction of aggregates), additional intermolecular associations were formed between soil constituents thus conferring greater stability on aggregates. This resulted in reduced dispersion (and the release of particles <0.04 mm in diameter) from the surfaces of aggregates and slaked aggregate fragments following rapid rewetting. As a consequence stability as measured by Turbidimetry was increased by drying. For aggregates from a predominantly arable history, this stabilization was not great enough to prevent slaking occurring following rapid rewetting, with the formation of a large proportion of stabilized fragments <0.5 mm in diameter. The stability of these aggregates as measured by wet sieving was therefore decreased by drying.
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Effect of sample pretreatment on aggregate stability measured by wet sieving or Turbidimetry on soils of different cropping history
Journal of Soil Science, 1993Co-Authors: R J HaynesAbstract:SUMMARY The effects of cropping history (pasture or arable) and sample pretreatment (field-moist, air-dried or air-dried and then tension or vacuum rewetted) on aggregate stability as measured by wet sieving or Turbidimetry were compared. When field-moist samples were used there was a tendency for aggregate stability, as measured by wet sieving, to decline with increasing time under arable cropping (i.e. decreasing soil organic matter content). Air-drying samples caused a pronounced decline in stability of soils from under arable management and as a consequence there was a marked decline in stability with increasing time under arable. Use of tension or vacuum rewetted samples resulted in high values of stability which were unaffected by cropping history. For Turbidimetry, there was a marked decline in measured stability with increasing time under arable cropping when field-moist samples were used. Air-drying caused an increase in measured stability that was relatively greater for the less stable samples. In comparison with air-dried samples, tension and vacuum rewetting caused a decrease in stability values for relatively unstable soils. It is suggested that, upon air-drying (and contraction of aggregates), additional intermolecular associations were formed between soil constituents thus conferring greater stability on aggregates. This resulted in reduced dispersion (and the release of particles