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Adsorption of charged and neutral polymer chains on silica surfaces: The role of electrostatics, volume exclusion, and hydrogen bonding
Spruijt, E. ; Biesheuvel, P.M. ; Vos, W.M. de - \ 2015
Physical Review. E, Statistical nonlinear, and soft matter physics 91 (2015). - ISSN 2470-0045 - 11 p.
polyelectrolyte adsorption - double-layer - free-energy - poly(vinylpyrrolidone) - relaxation - desorption - stability - kinetics - colloids - density
We develop an off-lattice (continuum) model to describe the adsorption of neutral polymer chains and polyelectrolytes to surfaces. Our continuum description allows taking excluded volume interactions between polymer chains and ions directly into account. To implement those interactions, we use a modified hard-sphere equation of state, adapted for mixtures of connected beads. Our model is applicable to neutral, charged, and ionizable surfaces and polymer chains alike and accounts for polarizability effects of the adsorbed layer and chemical interactions between polymer chains and the surface. We compare our model predictions to data of a classical system for polymer adsorption: neutral poly(N-vinylpyrrolidone) (PVP) on silica surfaces. The model shows that PVP adsorption on silica is driven by surface hydrogen bonding with an effective maximum binding energy of about 1.3kBT per PVP segment at low pH. As the pH increases, the Si-OH groups become increasingly dissociated, leading to a lower capacity for H bonding and simultaneous counterion accumulation and volume exclusion close to the surface. Together these effects result in a characteristic adsorption isotherm, with the adsorbed amount dropping sharply at a critical pH. Using this model for adsorption data on silica surfaces cleaned by either a piranha solution or an O2 plasma, we find that the former have a significantly higher density of silanol groups.
Limited Reversibility of Bioconcentration of Hydrophobic Organic Chemicals in Phytoplankton
Koelmans, A.A. - \ 2014
Environmental Science and Technology 48 (2014)13. - ISSN 0013-936X - p. 7341 - 7348.
granular activated carbon - selenastrum-capricornutum - polychlorinated biphenyl - kinetics - sediment - water - chlorobenzenes - desorption - sorption - fluxes
Aging, reversibility and desorption rates for the binding of hydrophobic chemicals (HOC) to phytoplankton cells have not been directly measured. Here the effect of bioconcentration time on subsequent desorption of hexachlorobenzene (HCB) and polychlorinated biphenyls (PCBs) was studied for the alga Monoraphidium minutum. Cell suspensions were exposed to HCB and PCBs spanning a range of logKow values of 5.7 to 8.2, for 0.13 to 14 d. Subsequently, reversibility and desorption rates were assessed by extracting the chemicals from the cells using infinite sink extractions with Tenax beads or Empore disks employed in the cell suspension. Uptake was biphasic with constant relative contributions of fast surface sorption. Desorption was biphasic too and fitted well to a first order two compartment model. Increasing exposure times resulted in increasing slowly desorbing chemical fractions and decreased desorption rates from these fractions. For the most hydrophobic PCBs, slowly desorbing fractions were >80-90%, whereas desorption half-lives from these fractions ranged up to 120 days. The slow desorption rates directly prove that bioconcentration to algae can be rate limited and imply that already after a few hours of exposure HOCs may become practically unavailable for repartitioning.
Kinetics of hydrophobic organic contaminant extraction from sediment by granular activated carbon
Rakowska, M.I. ; Kupryianchyk, D. ; Smit, M. ; Koelmans, A.A. ; Meent, D. van de - \ 2014
Water Research 51 (2014). - ISSN 0043-1354 - p. 86 - 95.
bodemverontreiniging - waterbodems - actieve kool - polycyclische koolwaterstoffen - soil pollution - water bottoms - activated carbon - polycyclic hydrocarbons - polycyclic aromatic-hydrocarbons - polychlorinated-biphenyls - mass-transfer - intraparticle diffusion - sorption kinetics - marine sediment - black carbon - amendment - desorption - polyoxymethylene
Ex situ solid phase extraction with granular activated carbon (GAC) is a promising technique to remediate contaminated sediments. The methods' efficiency depends on the rate by which contaminants are transferred from the sediment to the surface of GAC. Here, we derive kinetic parameters for extraction of polycyclic aromatic hydrocarbons (PAH) from sediment by GAC, using a first-order multi-compartment kinetic model. The parameters were obtained by modeling sediment-GAC exchange kinetic data following a tiered model calibration approach. First, parameters for PAH desorption from sediment were calibrated using data from systems with 50% (by weight) GAC acting as an infinite sink. Second, the estimated parameters were used as fixed input to obtain GAC uptake kinetic parameters in sediment slurries with 4% GAC, representing the ex situ remediation scenario. PAH uptake rate constants (kGAC) by GAC ranged from 0.44 to 0.0005 d-1, whereas GAC sorption coefficients (KGAC) ranged from 105.57 to 108.57 L kg-1. These values are the first provided for GAC in the presence of sediment and show that ex situ extraction with GAC is sufficiently fast and effective to reduce the risks of the most available PAHs among those studied, such as fluorene, phenanthrene and anthracene.
Rapid control of Chinese star anise fruits and teas for neurotoxic anisatin by Direct Analysis in Real Time (DART) high resolution mass spectrometry
Shen, Y. ; Beek, T.A. van; Claassen, F.W. ; Zuilhof, H. ; Chen, B. ; Nielen, M.W.F. - \ 2012
Journal of Chromatography. A, Including electrophoresis and other separation methods 1259 (2012). - ISSN 0021-9673 - p. 179 - 186.
illicium-anisatum - gas-chromatography - ambient conditions - verum - identification - consumption - infants - intoxication - adulterant - desorption
After ingestion, products containing Chinese star anise (Illicium verum) contaminated or adulterated with Japanese star anise (Illicium anisatum) or other Illicium species, can cause epilepsy, hallucinations, and nausea due to the rare neurotoxic sesquiterpene dilactone anisatin that is present in Japanese star anise. Thus a rapid, simple and unambiguous method for distinguishing between the morphologically similar Chinese star anise and toxic Japanese star anise is important for food safety issues. Direct Analysis in Real Time (DART) ambient ionisation coupled with orbitrap high resolution mass spectrometry allowed the recording of mass spectra of anisatin in solid star anise fruits in seconds without any prior sample pretreatment. Spectra could be obtained in both positive ([M+NH4]+ at m/z 346.1496, C15H24NO8) and negative mode ([M-H]- at m/z 327.1074, C15H19O8) and gave the same outcome provided a mass resolution of at least 27,000 is available. The anisatin signal was typically >1000 times larger in Japanese star anise than in Chinese star anise thus allowing an unequivocal qualitative determination. Herbal teas containing star anise fragments too small to be visually recognised, could be analysed by preparing a tea in 6 min and subsequently sampling ~2 µL of tea on a glass rod. None of the 8 investigated retail teas contained significant quantities of anisatin. Spiking a complex herbal tea containing Chinese star anise with an equally concentrated tea prepared from Japanese star anise provided a linear calibration curve (R2 = 0.995) after normalising on a native constituent of Chinese star anise (standard addition method). This showed that adulteration down to 1% (w/w) is still measurable. Compared with existing PCR, TLC, GC–MS and HPLC–ESI-MS/MS procedures, the proposed DART–HRMS procedure is faster and simpler and moreover measures the actual biotoxin
Nalevering van fosfor naar het oppervlaktewater vanuit de waterbodem : metingen in een veengebied in de Krimpenerwaard
Gerven, L.P.A. van; Hendriks, R.F.A. ; Harmsen, J. ; Beumer, V. ; Bogaart, P.W. - \ 2011
Wageningen : Alterra (Alterra-rapport 2217) - 49
veenweiden - desorptie - bodemchemie - fosfor - oppervlaktewaterkwaliteit - waterkwaliteit - krimpenerwaard - peat grasslands - desorption - soil chemistry - phosphorus - surface water quality - water quality
Het oppervlaktewater in de veenweidepolder de Krimpenerwaard kenmerkt zich door hoge fosforconcentraties in het zomerhalfjaar, gemiddeld vijf keer hoger dan de Kaderrichtlijn Water norm van 0,22 mg/l. De hoge concentraties kunnen niet worden verklaard door de bronnen die het oppervlaktewater dan belasten. De hypothese is dat de waterbodem de hoge concentraties in de zomer veroorzaakt door in het winterhalfjaar fosfor te adsorberen, fosfor afkomstig van de bronnen die het oppervlaktewater dan belasten, om dit fosfor in het zomerhalfjaar door desorptie na te leveren aan het oppervlaktewater. Deze hypothese is onderzocht door op een aantal locaties in de Krimpenerwaard de waterbodem te bemonsteren en te analyseren op het vermogen om fosfor na te leveren. Dit vermogen blijkt groot te zijn, meer dan voldoende om de hoge fosforconcentraties in het zomerhalfjaar te veroorzaken.
The interaction of boron with goethite: Experiments and CD-MUSIC modeling
Goli, E. ; Rahnemaie, R. ; Hiemstra, T. ; Malakouti, M.J. - \ 2011
Chemosphere 82 (2011)10. - ISSN 0045-6535 - p. 1475 - 1481.
surface structural approach - solid-solution interface - charge-distribution - ion adsorption - boric-acid - humic-acid - silicic-acid - ferric-oxide - soils - desorption
Boron (B) is an essential element for plants and animals growth that interacts with mineral surfaces regulating its bioavailability and mobility in soils, sediments, and natural ecosystems. The interaction with mineral surfaces is quite important because of a narrow range between boron deficiency and toxicity limits. In this study, the interaction of boric acid with goethite (a-FeOOH) was measured in NaNO3 background solution as a function of pH, ionic strength, goethite and boron concentration representing as adsorption edges and isotherms. Boron adsorption edges showed a bell-shaped pattern with maximum adsorption around pH 8.50, whereas adsorption isotherms were rather linear. The adsorption data were successfully described with the CD-MUSIC model in combination with the Extended Stern (ES) model. The charge distribution (CD) of inner-sphere boron surface complexes was calculated from the geometry optimized with molecular orbital calculations applying density functional theory (MO/DFT). The CD modeling suggested dominant binding of boric acid as a trigonal inner-sphere complex with minor contributions of a tetrahedral inner-sphere complex (at high pH) and a trigonal outer-sphere complex (at low pH). The interpretation with the CD model is consistent with the spectroscopic observations. © 2010 Elsevier Ltd.
Electrospun Polyurethane Fibers for Absorption of Volatile Organic Compounds from Air
Scholten, E. ; Bromberg, L. ; Rutledge, G.C. ; Hatton, T.A. - \ 2011
ACS Applied Materials and Interfaces 3 (2011). - ISSN 1944-8244 - p. 3902 - 3909.
shape-memory polyurethane - activated carbon - block-copolymers - polymer nanofibers - hard segment - adsorption - membranes - vapors - desorption - sorption
Electrospun polyurethane fibers for removal of volatile organic compounds (VOC) from air with rapid VOC absorption and desorption have been developed. Polyurethanes based on 4,4-methylenebis(phenylisocyanate) (MDI) and aliphatic isophorone diisocyanate as the hard segments and butanediol and tetramethylene glycol as the soft segments were electrospun from their solutions in N,N-dimethylformamide to form micrometer-sized fibers. Although activated carbon possessed a many-fold higher surface area than the polyurethane fiber meshes, the sorption capacity of the polyurethane fibers was found to be similar to that of activated carbon specifically designed for vapor adsorption. Furthermore, in contrast to VOC sorption on activated carbon, where complete regeneration of the adsorbent was not possible, the polyurethane fibers demonstrated a completely reversible absorption and desorption, with desorption obtained by a simple purging with nitrogen at room temperature. The fibers possessed a high affinity toward toluene and chloroform, but aliphatic hexane lacked the necessary strong attractive interactions with the polyurethane chains and therefore was less strongly absorbed. The selectivity of the polyurethane fibers toward different vapors, along with the ease of regeneration, makes them attractive materials for VOC filtration.
Langetermijneffecten van verminderde fosfaatgiften
Salm, C. van der; Schoumans, O.F. - \ 2011
Wageningen : Wettelijke Onderzoekstaken Natuur & Milieu (WOt-werkdocument 223) - 52
fosformeststoffen - bodemchemie - fosfaten - bodemvruchtbaarheid - nutrientenbeheer - milieubeleid - desorptie - simulatiemodellen - nederland - phosphorus fertilizers - soil chemistry - phosphates - soil fertility - nutrient management - environmental policy - desorption - simulation models - netherlands
Het huidige fosfaatbeleid richt zich op het verminderen van de fosfaatgiften om zodoende de fosfaatophoping in de bodem te stoppen en de verliezen van fosfaat naar het oppervlaktewater te verlagen. In deze studie wordt ingegaan op de mogelijkheid om de effecten van verminderde fosfaatgift op bodemvruchtbaarheid en uitspoeling te voorspellen. Om dit doel te bereiken, zijn gegevens van bestaande proeven verzameld en is het gedrag van fosfaat gesimuleerd op basis van de concepten die in het nutrientenemissiemodel STONE worden gehanteerd. Uit het onderzoek blijkt dat bij een juiste instelling van de desorptieparameters het gedrag van fosfaat goed kan worden gesimuleerd. Het instellen van de juiste waarde voor de desoptieparameters is echter complex omdat: de desorptiesnelheid afhangt van de mate van oplading van de grond en desorptiesnelheden in het veld lager zijn dan onder laboratoriumcondities wordt vastgesteld.
Effect of 1-1 electrolyte concentration on the adsorption/desorption of copper ion on synthetic birnessite
Wang, M. ; Wang, Y. ; Tan, W. ; Liu, F. ; Feng, X. ; Koopal, L.K. - \ 2010
Journal of Soils and Sediments 10 (2010)5. - ISSN 1439-0108 - p. 879 - 885.
heavy-metal ions - redox reactions - oxide minerals - adsorption - manganese - fe - desorption - hydroxides - surfaces - sorption
Oxides are ubiquitous in nature and play an important role in scavenging metal ions from soils and sediments. At the common pH range of the natural environment the well-studied Fe and Al oxides mostly carry a positive charge and adsorbed amounts of heavy metals, and their desorption percentages decrease with increasing ionic strength. The less well studied but also important Mn oxides possess negative charges in the natural environment and this will lead to a different behavior. Therefore, it is useful to further investigate how the electrolyte concentration and type affect the metal ion adsorption/desorption by Mn oxides. The phyllomanganate birnessite was synthesized with hydrochloric acid and potassium permanganate, and characterized by X-ray diffraction and transmission electron microscopy. The point of zero charge and specific surface area (SSA) were determined by, respectively, the rapid potentiometric titration method and BET-N(2) method. The adsorption was measured after shaking the samples in contact with Cu(NO(3))(2) solution for 2 h and further equilibration for 22 h at pH 4.5 and 25 +/- 1A degrees C. The 1-1 electrolyte concentrations were adjusted to 0, 0.001, 0.01, 0.1, 0.5, and 1 mol L(-1) KNO(3) or KCl. The PZC and SSA of synthetic birnessite were 2.5 and 75 m(2) g(-1), respectively. The birnessite consisted of small needle-like particles. A maximum amount of Cu(2+) adsorbed on birnessite of 208 +/- 8 mmol kg(-1) and 2.77 +/- 0.11 A mu mol m(-2) by using the BET area is obtained. The adsorption amount decreased gradually with increasing ionic strength. This is primarily due to screening of the electrostatic attraction. For the same reason the percentage of desorption of Cu(2+) previously adsorbed on birnessite increased with increasing electrolyte concentration. Furthermore, the decrease of Cu(2+) adsorption with increasing ionic strength was higher in KCl solution than in KNO(3) solution. This difference is most likely related to Cu(2+)-Cl(-) complexation. The type and concentration of 1-1 electrolyte affect the Cu(2+) adsorption/desorption characteristics on Mn oxide. The amounts of Cu(2+) adsorbed on birnessite reduced, and the desorption percentage increased with increasing 1-1 electrolyte concentration. These results are opposite to that of metal ion binding to positive Fe and Al oxides. The principal differences can be explained on the basis of generic electrostatic effects.
Evaluation of an approach for the characterization of reactive and available pools of twenty potentially toxic elements in soils: Part I – The role of key soil properties in the variation of contaminants’ reactivity
Rodrigues, S.M. ; Henriques, B. ; Ferreira da Silva, E. ; Pereira, M.E. ; Duarte, A.C. ; Romkens, P.F.A.M. - \ 2010
Chemosphere 81 (2010)11. - ISSN 0045-6535 - p. 1549 - 1559.
iberian pyrite belt - heavy-metals - acid soils - organic-matter - trace-elements - mercury - extraction - sediments - desorption - speciation
Harmful effects of potentially toxic elements (PTE’s) in soils relate to their geochemically reactive fraction. To assess the degree of the reactivity, specific extractions or models are needed. Here we applied a 0.43 M HNO3 chemical extraction to assess reactive pools of a broad range of PTE’s in 136 contaminated and non-contaminated soils. Furthermore we derived Freundlich-type models based on commonly available soil properties (pH, organic carbon and clay) as well as extended models that used other properties such as amorphous Al and Fe oxides and evaluated their possible use in risk assessment. The approach allowed to predict the reactivity of As, Hg, Co, U, Ba, Se, Sb, Mo, Li, Be (r2: 0.55–0.90) elements not previously included in such studies, as well as that of Cd, Zn, Cu, Pb, Ni and Cr (r2: 0.73–0.90). The inclusion of pH, organic carbon and clay improved the performance of all models except for Be and Mo, although the role of clay is not completely clear and requires further investigation. The ability of amorphous metal oxides to affect the reactivity of As, Hg, Cu, Ni, Cr, Sb, Mo and Li was expressed by the models in agreement with known geochemical processes leading to the retention of PTE’s by the solid matrix. Hence, such approach can be a useful tool to account for regional differences in soil properties during the identification of risk areas and constitute a significantly more powerful tool than the analysis of total pools of PTE’s in soils.
Nonylphenol mass transfer from field-aged sediments and subsequent biodegradation in reactors mimicking different river conditions
Weert, J.P.A. de; Streminska, M.A. ; Hua, D. ; Grotenhuis, J.T.C. ; Langenhoff, A.A.M. ; Rijnaarts, H.H.M. - \ 2010
Journal of Soils and Sediments 10 (2010)1. - ISSN 1439-0108 - p. 77 - 88.
fresh-water - lakes - alkylphenols - desorption - kinetics - octylphenol - ecosystems - events
Sediments can function as secondary source for water pollution of aerobically biodegradable non-halogenated organic compounds, which are persistent in anaerobic sediments. The mass transfer of compounds from sediment to bulk water depends on hydraulic conditions. In this study, desorption, mass transfer and biodegradation are investigated under settled and resuspended sediment conditions for branched nonylphenol (NP), which was used as model compound for aerobically biodegradable and anaerobic persistent compounds. Continuous flow through reactor experiments were performed in duplicate with aged NP polluted sediment under sterile and non-sterile conditions to investigate the mass transfer and combined mass transfer and biodegradation. The mass transfer of NP from the sediment bed to the bulk water decreased from 5.1 +/- 0.6 mu g d(-1) to a stable value of 0.3 +/- 0.02 mu g d(-1). The desorbed NP in the non-sterile reactors was biodegraded in the first 20 days of the experiment. At the end of the settled sediment conditions, the biodegradation became very limited, and the mass transfer was comparable to the mass transfer under sterile conditions. Upon resuspension, the NP concentration in the bulk water increased instantaneously in all reactors with a factor of 100. This immediate, increased mass transfer of NP from the sediment was larger than the amount that can be biodegraded under optimal conditions. Under non-sterile conditions, a second increase in the mass transfer was observed. However, the amount of desorbing NP during this second increase in mass transfer can be biodegraded under optimal environmental conditions. NP desorbs continuously at low concentrations from the sediment bed into the bulk water, which can almost be completely biodegraded. Resuspension of NP-polluted sediment initially led to an increase in the desorbing NP concentrations and can be followed by a subsequent reduction of the concentrations due to biodegradation under environmental conditions where biodegradation of NP can occur.
Estimation of In Situ Sediment-to-Water Fluxes of Polycyclic Aromatic Hydrocarbons, Polychlorobiphenyls and Polybrominated Diphenylethers
Koelmans, A.A. ; Poot, A. ; Lange, H.J. de; Velzeboer, I. ; Harmsen, J. ; Noort, P.C.M. van - \ 2010
Environmental Science and Technology 44 (2010)8. - ISSN 0013-936X - p. 3014 - 3020.
hydrophobic organic-compounds - contaminated sediments - black carbon - hudson river - polychlorinated-biphenyls - desorption - sorption - release - model - soot
Sediment--water fluxes of hydrophobic organic chemicals (HOC) may affect the quality of surface waters. Here, we present an approach to derive such fluxes from (a) in situ HOC concentration gradients measured with passive samplers and (b) mass transfer coefficients measured with a novel flux method using Empore disks. For eight undisturbed sediments, this method identified whether the sediment acted as a source or as a sink for HOCs. The analysis also identified which type of transport resistance governed sediment water exchange. For seven inland locations, exchange was limited by benthic boundary layer transport, showing no dependencies on sediment or chemical properties other than concentration. For one river mouth location, exchange was limited by slow in-bed intraparticle diffusion. A biphasic dual compartment radial diffusion model adequately described the data for this location. Fast desorption was interpreted as molecular diffusion retarded by microscale dual domain sorption to amorphous as well as black carbon (BC). Slow desorption was invariant with LogKow and consistent with intraorganic matter diffusion through BC particles. Finally, it is discussed how these findings can be translated into a general framework for flux based exposure assessment.
Triple domain in situ sorption modeling of organochlorine pesticides, polychlorobiphenyls, polyaromatic hydrocarbons, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans in aquatic sediments
Koelmans, A.A. ; Kaag, N.H.B.M. ; Sneekes, A.C. ; Peeters, E.T.H.M. - \ 2009
Environmental Science and Technology 43 (2009)23. - ISSN 0013-936X - p. 8847 - 8853.
black carbon - accumulation factors - organic-chemicals - land biotreatment - equilibrium - oil - extraction - desorption - bioavailability - quantification
Here we analyze the potential of black carbon (BC) and oil-inclusive models to explain in situ sorption of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD), organochlorine pesticides (OCP), polychlorobiphenyls (PCB), polyaromatic hydrocarbons (PAH), polychlorinated dibenzo-p-dioxins (PCDD), and polychlorinated dibenzofurans (PCDF) to harbor sediments. Such models are important to understand bioavailability and mobility limitations of these chemicals in the aquatic environment. Separate BC- or oil-inclusive models have been described before. However, it is unclear whether oil could dominate in situ sorption in sediments that also contain BC, and whether the relative importance of phases would differ for different compounds. A BC- and oil-inclusive model was evaluated against chemical data and measured sediment characteristics. Parameter uncertainty was assessed using Monte Carlo simulations. Fitted model parameters were consistent with literature data and were satisfactory from a statistical as well as a chemical perspective. Sorption to oil was strong, proportional to octanol-water partitioning (Log Kow) and of similar magnitude for OCP, PCB, PCDD, and PCDF. For PAH a single oil sorption coefficient was found. Oil dominated sorption only for PCBs, at oil levels above 50-250 mg oil/kg sediment. BC dominated sorption of most other compounds, especially high molecular PAHs, PCDD, and PCDFs.
Phosphorus removal from soil using Fe oxide-impregnated paper: Processes and applications
Los, A.M.D. ; Temminghoff, E.J.M. ; Schenkeveld, W.D.L. ; Hiemstra, T. ; Riemsdijk, W.H. van - \ 2009
Geoderma 151 (2009)3-4. - ISSN 0016-7061 - p. 282 - 289.
p-i test - filter-paper - available phosphorus - ionic-strength - phosphate - adsorption - goethite - desorption - extraction - aluminum
Fe oxide-impregnated paper (Pi-paper) is used as an artificial Phosphorus (P) sink to study P availability in soils and runoff. Pi-papers were introduced as they would mimic P uptake by plant roots by decreasing the P concentration in solution to negligibly low levels and thus enhancing P desorption from the soils solid phase. The rate of transfer of P from soil to Pi-paper would thus be limited by the soil P desorption rate. The maximum desorption rate is indeed achieved when the original method is used in which (at least) four Pi-papers per gram soil are placed in a soil suspension (soil–solution ratio of 0.025 kg L- 1). In several studies this method has however been adapted depending on the research question of interest without investigating the effect of this adaptation to the processes involved in the transfer of P from soil to Pi-paper. The aim of this study is to improve our understanding of the processes that occur in the Pi-paper–solution–soil system and so to extend the theoretical basis of this method. Insight is gained in these processes by comparing the experimentally determined P transfer from soil to Pi-paper with P transfer that is modeled based on the measured P concentration in solution and the (kinetic) Langmuir equation of the Pi-paper. P adsorption by a Pi-paper from standard solutions is not instantaneous but can be described with a kinetic Langmuir equation that is a characteristic of the Pi-paper. Over time, the Pi-paper reaches equilibrium with the solution, and the kinetic Langmuir equation can be rewritten to a Langmuir equation. Regardless if there is equilibrium or not, P adsorption to the Pi-paper is a function of the P concentration in solution. By adding Pi-paper to a soil suspension, a re-distribution of P takes place between the reactive surface area of the soil and the new reactive surface area of the Pi-paper that initially contains no adsorbed phosphate. As opposed to the original method where the desorption rate was limiting the overall P transfer, the adsorption rate to the Pi-paper is limiting when one Pi-paper per gram soil is placed in a soil suspension (soil–solution ratio of 0.1 kg L- 1). In this situation, the P concentration in solution is found to be in equilibrium with the soil's solid phase. With increasing contact time (> ~ 24 h) the whole system approaches equilibrium. With each successive Pi-paper newly added, more P is removed from the soil system and the decrease of P in solution will be governed by the soil P desorption isotherm. Varying the number of Pi-papers and the soil to solution ratio thus has a large effect on the transfer rate between soil and Pi-paper and if either the soil desorption rate, the Pi-paper adsorption rate or a combination limits this transfer rate. With increased insight in the P transfer between soil and Pi-paper sink, it becomes possible to tailor the experimental design to help answer the research question one is interested in.
Volume Overload Cleanup: An Approach for On-line SPE-GC, GPC-GC and GPC-SPE-GC
Kerkdijk, H. ; Mol, J.G.J. ; Nagel, B. van der - \ 2007
Analytical Chemistry 79 (2007)21. - ISSN 0003-2700 - p. 7975 - 7983.
chromatography-gas-chromatography - solid-phase extraction - performance liquid-chromatography - size-exclusion chromatography - residue analysis - oil - interface - water - pesticides - desorption
A new concept for cleanup, based on volume overloading of the cleanup column, has been developed for on-line coupling of gel permeation chromatography (GPC), solid-phase extraction (SPE), or both, to gas chromatography (GC). The principle is outlined and the applicability demonstrated by the determination of pesticide residues in food matrixes using integrated and automated cleanup-GC¿MS. Compared to conventional approaches for on-line cleanup-GC, the new technique involves introduction of much smaller volumes (e.g., 2¿20 ¿L) into the GC without sacrificing method LODs. The much smaller injection volumes involved greatly simplify on-line coupling, improve robustness, and increase attractiveness for implementation in routine laboratories.
Impact of polychlorinated biphenyl and polycyclic aromatic hydrocarbon sequestration in sediment on bioaccumulation in aquatic food webs
Moermond, C.T.A. ; Roessink, I. ; Jonker, M.T.O. ; Meijer, T. ; Koelmans, A.A. - \ 2007
Environmental Toxicology and Chemistry 26 (2007)4. - ISSN 0730-7268 - p. 607 - 615.
hydrophobic organic-chemicals - black carbon - benthic organisms - contact time - bioavailability - desorption - sorption - lake - accumulation - extraction
It is not clear whether sequestration or aging of organic chemicals like polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) limits accumulation in higher levels of aquatic food chains. Therefore, the effect of aging on accumulation was studied in 1-m3 model ecosystems that mimicked fish-dominated, macrophyte-dominated, and fish- and macrophyte-dominated shallow lakes. Also treatments without fish and macrophytes were included. General characteristics, biomasses, total (Soxhlet-extractable), and labile (6-h Tenax-extractable) PCB and PAH concentrations in sediment and biota were monitored over time. Accumulation data for PCB 28, PCB 149, and fluoranthene (native to the sediment taken from the field) were compared to those for spiked analogues PCB 29, PCB 155, and fluoranthene-d10. Labile fractions for spiked compounds were higher than for their native analogues and decreased over time, suggesting sequestration in the sediment. In the majority of cases, 6-h Tenax-extractable concentrations correlated better with concentrations in biota than Soxhlet-extractable concentrations. Ecosystem structure affected food web accumulation, but replicate variability was too high to detect clear treatment effects. Differences in accumulation between spiked compounds and their native analogues indicated an effect of aging for invertebrates, macrophytes, and benthivorous fish. Thus, aging may translate directly into reduced uptake at higher trophic levels.
Supramolecular polymers in inhomogeneous systems
Zweistra, H.J.A. - \ 2007
Wageningen University. Promotor(en): Gerard Fleer, co-promotor(en): N.A.M. Besseling. - [S.l.] : S.n. - ISBN 9789085045526 - 78
polymeren - adsorptie - desorptie - fractionering - zuiveren - fysicochemische eigenschappen - supramoleculaire chemie - polymers - adsorption - desorption - fractionation - purification - physicochemical properties - supramolecular chemistry
Diffusion and exchange of adsorbed polymers studied by Monte Carlo simulations
Klein Wolterink, J. ; Barkema, G.T. ; Cohen Stuart, M.A. - \ 2005
Macromolecules 38 (2005)5. - ISSN 0024-9297 - p. 2009 - 2014.
competitive adsorption - poly(ethylene oxide) - gel-electrophoresis - reptation dynamics - solid-surface - repton model - kinetics - desorption - statics - chain
Monte Carlo simulations are performed of adsorbed polymers with various polymer lengths N and adsorption energies ¿s. Exchange times and the rates of lateral diffusion (along the surface) are investigated as a function of N and ¿s. Lateral diffusion is found to be a combination of reptation (diffusion of stored length along the chain) which is hardly affected by ¿s and dominates for longer polymers, and Rouse-like behavior (sideways movement), which is strongly affected by ¿s and dominates for shorter polymers. We relate the characteristic time for exchange of adsorbed polymers, as a function of polymer length N and adsorption energy ¿s, to the bulk diffusion coefficient at the surface density, to the polymer length and to the ratio of the surface and bulk densities. The differences of 2 and 3 orders in magnitude of the exchange times at fixed ¿s and N, respectively, can thus be reduced to factors of 4 and 2.
An improved experimental and regression methodology for sorption isotherms
Quirijns, E.J. ; Boxtel, A.J.B. van; Loon, W.K.P. van; Straten, G. van - \ 2005
Journal of the Science of Food and Agriculture 85 (2005)2. - ISSN 0022-5142 - p. 175 - 185.
equilibrium moisture-content - water activity - 3 temperatures - desorption - equations - products - fruit - foods - seeds - fufu
Sorption isotherms of corn and starch cylinders with immobilised catalase are experimentally determined at different temperatures for use in drying models in optimal control studies. This application of the sorption isotherm requires an accurate prediction of the sorption data at different temperatures for the low water activity range. The GAB equation is used for the prediction of the sorption isotherms. Two major problems are encountered by employing standard procedures, ie prediction of sorption at aw <0.11 and sensitivity of the GAB parameters to the applied data range. An improved methodology is developed, consisting of extending the standard experimental procedure with additional data points in the low water activity range and changing the criterion in the regression procedure in the sum of squares, which is weighed by the variance of the experimental data. The new methodology leads to accurate, consistent and physically relevant parameters of the GAB equation, which are independent of the applied data range in the regression analysis and which result in accurate predictions of the sorption behaviour at low water activity. The sorption data at different temperatures at low water activity can be predicted in the best way with parameters obtained after direct regression based on weighed SSQ.
Uit de mest- en mineralenprogramma's : Uitmijnen biedt perspectief om het risico van fosfaatuitspoeling uit zwaar bemeste landbouwgronden te verminderen!
Koopmans, G.F. ; Chardon, W.J. - \ 2004
Wageningen : Alterra (Informatieblad / Alterra 398.49) - 2
mest - landbouwgronden - zandgronden - fosfaat - verzwakking - desorptie - potproeven - bemesting - fosfaatuitspoeling - oppervlaktewaterkwaliteit - manures - agricultural soils - sandy soils - phosphate - attenuation - desorption - pot experimentation - fertilizer application - phosphate leaching - surface water quality
Landbouwgronden die in het verleden zwaar zijn bemest, zijn rijk aan fosfaat. In kalkloze zandgronden is de bindingscapaciteit van de bodem voor fosfaat niet groot, waardoor er een risico ontstaat voor uitspoeling. Dit gebeurt vooral in vlakke gebieden met een ondiepe grondwaterstand en een intensief afwateringsstelsel. In het oppervlaktewater leidt te veel fosfaat tot ongewenste effecten (eutrofiëring). In Nederland heeft momenteel ongeveer eenderde deel van de kalkloze zandgronden een (te) hoog fosfaatgehalte. Uitmijnen is een mogelijke maatregel om het risico van fosfaatuitspoeling uit kalkloze zandgronden met een te hoog fosfaatgehalte te verminderen. Onder uitmijnen wordt verstaan: het onttrekken van fosfaat aan de grond door middel van het oogsten en afvoeren van een gewas zonder fosfaatbemesting. In dit infoblad worden de belangrijkste resultaten weergegeven van een experiment, waarin het proces van uitmijnen versneld is nagebootst in een potproef. De afname in de hoeveelheid fosfaat in de grond en de veranderingen in de fosfaatspeciatie zijn onderzocht. Op basis van deze resultaten kunnen richtlijnen worden ontwikkeld voor het beheer van de zogenaamde fosfaatlekkende landbouwgronden in de buurt van oppervlaktewater, zodat in de toekomst voldaan kan worden aan de kwaliteitseisen van de Kaderrichtlijn Water