Koos J. Kroon

Delft University Of Technology, Delft, South Holland, Netherlands

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Publications (6)12.19 Total impact

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    ABSTRACT: Isotopic exchange based approaches have for many years been applied in soil and solute research. However, acquiring and elaboration of experimental data were not always straightforward and complete. A strict and correct use of combined isotopic exchange-compartmental analysis may widen the knowledge database and provide information not available as yet. The experiments were carried out with arsenic (arsenate) from IAEA-SOIL-5 in contact with water or phosphate solution in dynamic equilibrium. After contacting the soil suspension for 28 days, the amount of arsenate released is 2.8 and 6.3 % of arsenic (solutes) in the soil, respectively. Addition of a radioactive arsenate (73)As(V)-spike and following the distribution of this radiotracer from the aqueous to the solid phase in time shows that the accessible fraction, i.e. available for exchange, is in both cases 12%. This implies that the remainder of the arsenic is enclosed in the lattice of minerals and for that reason unavailable for exchange, at least on the time scale of the experiment (weeks). From deconvolution of compartmental analysis results the distribution of accessible arsenate in the soil could be attributed to sorption onto external surfaces (2.6 and 2.0% of total arsenic present for the water and phosphate system, respectively) and sorption onto internal surfaces after diffusion through soil particle pores (6.5 and 4.2% of total arsenic present for the water and phosphate system, respectively). The mean residence time in two out of three compartments was in the order of minutes for the external surfaces and in the order of days for the diffusion-controlled internal surfaces.
    No preview · Article · Apr 2008 · Talanta
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    ABSTRACT: The following parameters influencing the extraction efficiency of adsorbed arsenic (arsenate) from IAEA-SOIL-5 were investigated: (a) sonication or shaking time and temperature and (b) extractant type (MgCl 2 or NaH 2 PO 4 solution), concentration and pH. Sonication of 250 mg material for 1 h at < 30°C with 10 mL 1 mol L m 1 phosphate at pH 4.0 yielded a maximum arsenate extraction efficiency of 31.9%. The remainder of the arsenate is probably incorporated in the lattice of minerals and not easily available (exchangeable via ion exchange mechanisms).
    No preview · Article · Feb 2003 · International Journal of Environmental Analytical Chemistry
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    ABSTRACT: Solid-phase extraction (SPE) cartridges with different functional groups(chelating, ion-exchange, hydrophobic) may be useful for copper speciationdeterminations of aqueous samples. Provided that each cartridge selectivelyextracts one species or a group of species, a fast screening of copper speciationcan be achieved by performing a series of extractions with different SPE cartridgesand combining the results. For this purpose, the performance of five SPE cartridgeswas studied with respect to extraction selectivity using samples with knowncomposition. Samples were spiked with a high-specific 64 Cu radiotracer toachieve easy detection of extracted copper species. Its high radioactivityper unit of mass ensures preservation of initial chemical equilibria and compositionof the sample. Results show that secondary interactions may take place onthe extracting phase when relatively clean samples are analyzed. Two naturalwater samples, viz. a ditch water and a seawater sample, were exposed to aseries of extractions as well. Species distributions found for these samplesgenerally correspond to expected distributions. Secondary interactions maybe suppressed in these cases, as other metal species compete for these interactions.
    No preview · Article · Jan 2001 · Journal of Radioanalytical and Nuclear Chemistry
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    ABSTRACT: Using various chromatographic techniques (size exclusion, anion exchange, and cation exchange) combined with several detectors (neutron activation analysis and atomic fluorescence spectrometry), an attempt was made to characterize selenium compounds in some edible, selenium-accumulating mushrooms (Albatrellus pes-caprae and Boletus edulis). The mushrooms contained mostly low-molecular-weight (6 kDa) selenium compounds. After proteolysis, only a small fraction of the extractable selenium could be identified as selenite (3.0–9.2%, Albatrellus pes-caprae), selenocystine (minor, Albatrellus pes-caprae; 7.5%, Boletus edulis), or selenomethionine (1.0%, Boletus edulis), leaving the form of the bulk still to be elucidated.
    No preview · Article · Feb 2000 · Biological Trace Element Research
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    ABSTRACT: Voltammetry in cathodic stripping mode was used to measure ultratrace levels of copper in preparations of very high specific activity 64Cu produced via the 64Zn(n,p)64Cu reaction. With high-purity targets and reagents, strict acid-wash procedures and careful handling, specific activities of up to 4×1016 Bq g−1 at 8 h after EOB could be attained when irradiating in a high flux reactor. During irradiation also 65Cu is formed via the route 64Zn(n,γ)65Zn→65Cu, and this contribution to the total amount of copper in high specific activity 64Cu preparations is not always negligible.
    No preview · Article · Jul 1999 · Applied Radiation and Isotopes
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    ABSTRACT: The mushroom Agaricus bisporus was cultivated under controlled conditions to follow the simultaneous uptake of selenium and cesium from a mycelium-incubated substrate containing appropriate radiotracers (75Se, 134Cs). Cesium was chosen as a non-complexing cationic marker for tetravalent selenium which tends to undergo biotransformation and/or binding to reactive functional groups in the mushroom. During cultivation it was found that volatile selenium compounds can be adsorbed/absorbed by fruiting bodies. Mushroom homogenates originating from cap and stalk were separated by centrifugation into supernatant and pellet, and the former subjected to size fractionation chromatography. For both cap and stalk the recovery in supernatant was >90% for cesium and ca. 60% for selenium. Cesium gave the expected single cationic peak in the chromatogram whereas for selenium four and five compounds could be observed for stalk and cap, respectively. The extra low molecular weight or inorganic compound in cap might be related to high metabolic activity due to spore formation. The necessity of speciation is clearly illustrated, the more as the toxicity of the separated compounds and their resorption in humans are still to be elucidated.
    No preview · Article · Apr 1998 · Chemosphere