Bulk Solution Concentration Research Articles

Kinetic and equilibrium adsorption parameters estimation based on a heterogeneous intraparticle diffusion model

In this work, a commercial resin with a well-developed internal pore structure was chosen to adsorb four parabens used as probe molecules. The main novelty was to propose and validate a phenomenological transient adsorption model based on conservation law in both phases coupled with Langmuir’s equilibrium law and Fick’s mass transfer rate law inside the pores. With such an aim, a heterogeneous three-parameter intraparticle diffusion model, IPDM, was formulated, and its numerical solution was fitted to time-dependent concentration data by minimizing the sum of squared residuals. Equilibrium constants were also predicted by fitting Langmuir isotherm to equilibrium data. A monolayer capacity of 0.81 mmol/g was calculated for the four parabens regardless of the number of carbons in the ester group. With the optimal parameters values from the IPDM fitting process, a system of ODEs comprising local sensitivity coefficients as dependent variables was solved to compute the parameters’ variance-covariance matrix and infer their ranges for a 95% marginal confidence interval. In order to test the validity of the proposed model, an attempt to crosscheck between the parameters obtained by the estimation of the equilibrium related parameter, κ, and the modified capacity parameter, ξp′, and the ones obtained by fitting the Langmuir’s isotherm to equilibrium data was carried out. As far as equilibrium related parameters concern, there is a relative agreement inside the limits of the confidence range between the estimated values of the amount adsorbed in equilibrium with initial bulk solution concentration, q0, and Langmuir’s equilibrium constant, K, adjusted to kinetic and equilibrium data, independently. Additionally, the order of magnitude of pore diffusivity obtained in this work is in accordance with the one predicted by Wilke-Chang correlation and is inversely proportional to the van der Waals volume raised to the power 0.53 in close agreement with the literature.

Effects of soil surface electric field on aggregates breakdown and water erosion in black soil region of Northeast China

Through quantitatively adjust soil electric field, we investigated the effect of soil electric field on aggregate stability and soil erosion in black soil region of Northeast China with the experiments of wet sieving and rainfall simulation. Results showed that: 1) Soil surface potential absolute value and electric field strength increased with the decreases of electrolyte concentration in bulk solution. Soil electric field strength could reach to 108 V·m-1. 2) With the increase of soil electric field strength, the degree of fragmentation of soil aggregates increased and the mean weight diameter (MWD) decreased sharply first and then kept constant. 3) With decreasing electrolyte concentration and increasing surface potential, the amount of soil loss increased. As the electrolyte concentration was <0.01 mol·L-1, the corresponding soil surface potential was > 210 and 209 mV for Bin-xian and Keshan, respectively, the cumulative amounts of soil loss with rainfall time almost overlapped, suggesting that the electrolyte concentration of 0.01 mol·L-1 was the threshold for soil erosion. 4) There was a linear relationship between soil cumulative loss and MWD. Our results indicated that soil electric field strength increased as the rain enters into the soil, which could induce soil aggregate breakdown and release amounts of fine soil particles. Finally, soil erosion occurred under the driving of flowing water. Our results provided insights into the mechanism underlying soil erosion in the black soil region of Northeast China.

Addressing the sensitivity of signals from solid/liquid ambient pressure XPS (APXPS) measurement

Ambient pressure XPS has demonstrated its great potential in probing the solid/liquid interface, which is a central piece in electrocatalytic, corrosion, and energy storage systems. Despite the advantage of ambient pressure XPS being a surface sensitive characterization technique, the ability of differentiating the surface adsorbed species (∼Å scale) and bulk electrolyte (∼10 nm scale) in the spectrum depends on the delicate balance between bulk solution concentration (C), surface coverage (θ), bulk liquid layer thickness (L), and inelastic mean free path (λ) as a function of photon energy. By investigating a model system of gold dissolving in a bromide solution, the connection between theoretical prediction at the atomic resolution and macroscopic observable spectrum is established.

Bimodal stringence-mediated response of metal-detecting luminescent whole cell bioreporters: Experimental evidence and quantitative theory

Whole cell luminescent bacterial sensors are used to monitor the bioavailability and toxicity of metals in aquatic media. Any rationale of the time response of such metal-detecting biosensors necessarily asks for the so-far missing measurement and modeling of the impacts of medium nutritional quality on lux-reporter expression and bioluminescence production. In this work, improvement of nutritional conditions in bioluminescence assays by increasing amino acid concentration is shown to generate a transition from metal concentration-dependent monomodal to bimodal bell-shaped signal. The long-term component of the latter features a stringence-mediated adaptation of the cells to deficiency in nutrients supply from the medium. The demonstration is based on the analysis of the ∼17 h response of bioluminescent Escherichia coli engineered with luxCDABE reporter genes placed under the transcriptional control of a cadmium (0−22 nM bulk solution concentration) inductible-PzntA promoter or of the ribosomal RNA rrnB P1 promoter repressed by (p)ppGpp alarmones synthesized by cells in nutritional stress. The time-dependence of normalized PzntA-luxCDABE biosensor signal is successfully reproduced by our recent theory elaborated for the kinetics of bioluminescence emission by metal-responsive biosensors. The formalism allows assessment of luciferase half-life and of the time variations of cells photoactivity with medium composition. The theoretically-determined long-term kinetics of cell photoactivation is remarkably supported by independent measurements on the rrnB P1-luxCDABE bioreporter. Results clarify the origin of the mismatch between maxima in photoactive biomass and in bioluminescence over time, and they offer practical options for addressing contaminant toxicity via cell photoactivity derived from deconvolution of normalized biosensor response.

Detection of specific antibody-ligand interactions with a self-induced back-action actuated nanopore electrophoresis sensor

Recent advances in plasmonic nanopore technologies have enabled the use of concurrently acquired bimodal optical-electrical data for improved quantification of molecular interactions. This work presents the use of a new plasmonic nanosensor employing self-induced back-action (SIBA) for optical trapping to enable SIBA-actuated nanopore electrophoresis (SANE) for quantifying antibody-ligand interactions. T-cell receptor-like antibodies (TCRmAbs) engineered to target peptide-presenting major histocompatibility complex (pMHC) ligands, representing a model of target ligands presented on the surface of cancer cells, were used to test the SANE sensor’s ability to identify specific antibody-ligand binding. Cancer-irrelevant TCRmAbs targeting the same pMHCs were also tested as a control. It was found that the sensor could provide bimodal molecular signatures that could differentiate between antibody, ligand and the complexes that they formed, as well as distinguish between specific and non-specific interactions. Furthermore, the results suggested an interesting phenomenon of increased antibody-ligand complex bound fraction detected by the SANE sensor compared to that expected for corresponding bulk solution concentrations. A possible physical mechanism and potential advantages for the sensor’s ability to augment complex formation near its active sensing volume at concentrations lower than the free solution equilibrium binding constant (KD) are discussed.

A reduction‐dependent copper uptake pathway in an oceanic diatom

Copper(II) is reduced to Cu(I) extracellularly by marine and freshwater phytoplankton, but its biological significance is not firmly established. We studied the relationship between Cu(II) reduction and uptake in Thalassiosira oceanica, a diatom that was recently shown to possess functional copper uptake transporters (CTRs) that take up Cu(I). Inorganic and organic complexes of Cu(II) were reduced directly by reactions at the cell surface in proportion to Cu(II)‐ligand reduction potential. The rates of reduction were enhanced twofold in Cu‐limited cells, suggesting reduction was regulated by Cu nutritional state. Suppressing Cu(II) reduction caused a decrease in Cu uptake rate by 97% and addition of a Cu(I) complexing agent completely inhibited cell division and reduced Cu quota when Cu concentration was growth limiting. Thus, Cu(II) reduction was an obligatory first step in Cu uptake. Cu(II) reduction rate and growth rate of T. oceanica were proportional to Cu–ethylenediaminetetraacetic acid concentration and independent of inorganic Cu concentration in bulk solution. The results suggest that Cu(II) bound to organic ligands was reduced by extracellular cupric reductases and subsequently internalized. This reduction‐dependent uptake pathway may enable diatoms to use naturally occurring Cu(II) organic complexes in the sea.

Mixed ad/desorption kinetics unraveled with the equilibrium adsorption isotherm

Predicting ad/desorption rates at solid/solution interfaces is important for environmental and industrial processes. For non-porous surfaces the adsorption process can be divided in film diffusion and surface reactions. Classical models consider situations where one of these processes is rate limiting, but by considering a steady state situation of film diffusion and surface reactions a simple mixed kinetic model for ad/desorption of solutes or nano particles is obtained. With this model, the driving force for ad/desorption can be predicted when the equilibrium isotherm is known. The model can be combined either with experimentally meausured isotherms or with a large variety of equilibrium adsorption isotherm equations for mono- and (pseudo) multicomponent adsorption of charged and uncharged solutes on homogeneous and heterogeneous surfaces. The kinetic model is illustrated by using the Langmuir equation, and the relation between the adsorption affinity and the driving force for ad/desorption is discussed for controlled-flow and stirred batch experiments. With high-affinity isotherms adsorption is relatively fast and desorption is very slow. In batch systems the ad/desorption rates are smaller than in flow systems because the bulk solute concentration decreases with adsorption and increases with desorption. Experimental results for both flow and batch systems are used for a semi-quantitative comparison of the observed kinetics with model predictions based on the driving force for ad/desorption.

Elucidating conductivity-permselectivity tradeoffs in electrodialysis and reverse electrodialysis by structure-property analysis of ion-exchange membranes

Ion-exchange membranes (IEMs) are used in environmental and energy technologies of electrodialysis (ED) desalination and reverse electrodialysis (RED) power generation, respectively. Recent studies reported empirical evidence that the conductivity and permselectivity of IEMs are bound by a tradeoff relationship, where an increase in ionic conductivity is accompanied by a decrease in counterion selectivity over co-ion. A fundamental understanding of this conductivity-permselectivity tradeoff is principal to inform membrane development. This study presents an IEM transport model to analytically relate conductivity and permselectivity to intrinsic membrane chemical and structural properties. The model employs the Nernst-Planck transport framework and incorporates counterion condensation theory to simulate the performance of IEMs in a range of ED and RED operations. The analysis revealed the mechanism for the tradeoff induced by bulk solution concentration: a higher salinity suppresses IEM charge-exclusion, thus lowering permselectivity, but elevates mobile ion concentration within the membrane matrix to improve conductivity. As such, IEM applications are practically confined to sub-seawater salinities, i.e., RED using hypersaline streams will not be efficient. In another tradeoff driven by IEM water sorption, increasing membrane swelling enhances effective ion diffusivity to raise conductivity, but diminishes permselectivity due to dilution of fixed charges. The transport model indicates that increasing membrane ion-exchange capacity and reducing thickness can yield highly selective and conductive IEMs.

Impact of Solution Composition on the Resistance of Ion Exchange Membranes

Introduction: Resistance to ion transport in ion exchange membranes (IEMs) is detrimental to the performance of IEM-based processes such as electrodialysis (ED) and reverse electrodialysis (RED). IEM resistance depends on solution composition. However, such understanding is currently limited and of a qualitative nature (e.g., IEM resistance decreases with salt concentration in solution, multivalent ions increase IEM resistance). Therefore, a quantitative understanding of this dependency is needed to predict ED/RED performance. Accordingly, we measured the resistance of representative IEMs in single-solute solutions and used our results to draw quantitative and mechanistic conclusions. Methods: IEM resistance values were obtained using electrochemical impedance spectroscopy with the membrane mounted in a diffusion cell. The resistance of one representative cation (CEM) and one anion (AEM) exchange membrane was investigated in 15 single-solute solutions. Results: In general, membrane resistance for both the CEM and AEM decreased with increasing solution concentration. Membrane resistance was on the order of tens to hundreds of ohm.cm2 in dilute (<0.01M) solutions and a few to tens of ohm.cm2 in concentrated (>0.1M) solutions. The primary findings include: -Membrane resistance was sensitive to salt identity only in the case of the CEM, for which it depended on the counter-ion identity. -Membrane resistance increased with increasing hydration free energy of the counter-ion in bulk solution, indicating that steric effects are important determinants of membrane ionic resistance. -Membrane resistance had a strong inverse correlation with solution concentration below 0.1 M, and remained approximately constant at higher concentrations. -The dependence of membrane resistance on salt concentration in bulk solution was fitted well by a semi-empirical expression containing a concentration-independent term and a concentration-dependent term; the latter followed a non-linear dependence on bulk solution concentration. The non-linear dependence on bulk solution concentration suggests that the interconnectedness of the structural domains within the membrane that contribute to ionic resistance has a certain level of randomness. Future studies are required to fully understand the dependence of membrane ionic resistance on bulk solution concentration at low salt concentrations, including why membrane resistance depends on the co-ion identity only at relatively low salt concentrations (0.001-0.05 M). Conclusions: Overall, our analysis produced a quantitative understanding of the dependence of IEM resistance on the identity and properties of single-salt solutions, and contribute necessary information towards the development of a complete theory for IEM resistance. Specifically, we found that steric effects are a primary determinant of membrane resistance and that the structural domains are arranged randomly (as opposed to in series or parallel). Thus, future work to develop a complete IEM resistance theory should include (i) understanding how the hydration free energy of ions relates to their interactions with water and the membrane, (ii) elucidating how these interactions relate to ion mobility, and (iii) developing a mathematical model describing the random interconnectedness of structural membrane domains. Figure 1

Soil internal forces contribute more than raindrop impact force to rainfall splash erosion

Soil internal forces, including electrostatic, hydration and van der Waals, play critical roles in aggregate stability, erosion, and other processes related to soil and water. However, the extent to which soil internal forces influence splash erosion during rainfall remains unclear. In the present study, we used cationic-saturated soil samples to quantitatively separate the effects of soil internal and raindrop impact forces (external) on splash erosion through simulated rainfall experiments. An electrolyte solution was employed as rainfall material to represent the combined effects of soil internal and external forces on splash erosion. Ethanol was used to simulate the sole effect of soil external force on splash erosion. The soil splash erosion rate increased with increasing rainfall kinetic energy in experiments with electrolyte solution and ethanol and was also greatly influenced by soil internal forces. Moreover, the soil splash erosion rate increased first (from 1 to 10−2 mol L−1) then leveled off (from 10−2 to 10−4 mol L−1) with decreasing electrolyte concentration in the bulk solution. This finding was in agreement with the theoretical analysis of soil internal forces. The contribution rate of soil internal forces on splash erosion was >65% at a low electrolyte concentration (<10−2 mol L−1) and only 3%–25% at an electrolyte concentration of 1 mol L−1. Even though the electrolyte concentration of the soil bulk solution reached 10−1 mol L−1, the contribution rate of soil internal forces to splash erosion was >50%. Hence, soil internal forces exerted higher contribution to rainfall splash erosion than raindrop impact force under most field conditions. This work provides new understanding of the mechanism of soil splash erosion and establishes the possibility of controlling splash erosion by jointly regulating the soil internal and external forces.

Moringa oleifera Seed Protein Adsorption to Silica: Effects of Water Hardness, Fractionation, and Fatty Acid Extraction.

Motivated by the proposed use of cationic protein-modified sand for water filtration in developing nations, this study concerns the adsorption of Moringa oleifera seed proteins to silica surfaces. These proteins were prepared in model waters of varying hardness and underwent different levels of fractionation, including fatty acid extraction and cation exchange chromatography. Adsorption isotherms were measured by ellipsometry, and the zeta potentials of the resulting protein-decorated surfaces were measured by the rotating disk streaming potential method. The results indicate that the presence of fatty acids has little effect on the M. oleifera cationic protein adsorption isotherm. Adsorption from the unfractionated extract was indistinguishable from that of the cationic protein isolates at low concentrations but yielded significantly greater extents of adsorption at high concentrations. Adsorption isotherms for samples prepared in model hard and soft fresh waters were indistinguishable from each other over the measured bulk solution concentration range, but adsorption from hard or soft water was more extensive than adsorption from deionized water at moderate protein concentrations. Streaming potential measurements showed that adsorption reversed the net sign of the zeta potential of silica from negative to positive for all protein fractions and water hardness conditions at protein bulk concentrations as low as 0.03 μg/mL. This suggests that sands can be effectively modified with M. oleifera proteins using small amounts of seed extract under various local water hardness conditions. Finally, ellipsometry indicated that M. oleifera proteins adsorb irreversibly with respect to rinsing in these model fresh waters, suggesting that the modified sand would be stable on repeated use for water filtration. These studies may aid in the design of a simple, effective, and sustainable water purification device for developing nations.

Soil internal forces initiate aggregate breakdown and splash erosion

Soil erosion is a severe ecological and environmental problem and the main cause of land degradation in many places worldwide. Soil aggregate breakdown is the first key step of splash erosion and is strongly influenced by soil internal forces, including electrostatic, hydration, and van der Waals forces. However, little is known about the influence of soil internal forces on splash erosion. In this study, we demonstrated that both splash erosion rate (SER) and soil aggregate breaking strength (ABS) were significantly affected by soil internal forces. SER and ABS increased first (from 1 to 10−2 mol L−1) then became stable (from 10−2 to 10−4 mol L−1) with decreasing electrolyte concentration in bulk solution. The electrolyte concentration of 10−2 mol L−1 in bulk solution was the critical point for both soils in splash erosion and soil aggregate stability. The experimental results can be well interpreted by the theoretical analysis of soil internal forces. The surface potential and electric field around soil particles increased with decreasing electrolyte concentration, thereby increasing the electrostatic repulsive force among soil particles. This phenomenon led to soil aggregate breakdown and release of fine soil particles. Soil splash erosion rate and aggregate stability showed a linear relationship (R2 = 0.83). Our results suggest that soil internal forces induce soil aggregate breakdown and then release of fine soil particles when the soil was wetted, supplying the original material for splash erosion. Furthermore, the raindrop impact force is the driving mechanism causing soil particle movement. In summary, splash erosion could be due to the coupling effects of soil internal forces and the raindrop impact force. Our study provides a possible internal controlling method for reducing splash erosion by adjusting soil internal forces between soil particles.

Bromate electroreduction from acidic solution at spherical microelectrode under steady-state conditions: Theory for the redox-mediator autocatalytic (EC″) mechanism

Process of bromate reduction from aqueous acidic medium at (hemi)spherical microelectrode under steady-state conditions has been analyzed theoretically. Since bromate anion is non-electroactive within the potential range under consideration its transformation is based on the electroreduction of bromine which is present in bulk solution in small (even trace) amounts while the bromine reduction product, bromide anion, reacts irreversibly in acidic conditions with bromate anion, with regeneration of bromine, thus forming a redox mediator cycle. Similar to our previous studies of this process at rotating disk electrode it has been shown that this process possesses autocatalytic features, which may under certain conditions leads to considerable accumulation of the redox-couple components, Br2 and Br−, near the electrode surface. As a result the rate of the bromate transformation by the catalytic cycle becomes so rapid that the rate of the whole process is controlled by the bromate transport from the bulk solution to the kinetic layer near the electrode surface, i.e. the current becomes comparable to a very high BrO3− diffusion limited one. For such an autocatalytic passage of the process the radius of the microelectrode has to exceed a critical value which depends on the solution composition. This peculiarity of the system leads to the anomalous dependence of the maximal current density of the bromate reaction on the electrode size: if the electrode radius is under its critical value the current density is very small since it is determined by the discharge of bromine species from the bulk solution, with no significant transformation of bromate. On the contrary, for larger electrodes the autocatalytic EC″ mechanism becomes efficient and the passing current density can exceed the bromate diffusion limited one, i.e. it is a very strong one. The theory also predicts a complicated dependence of the maximal current on the bulk solution concentrations of bromate and protons.

Forward osmosis: Definition and evaluation of FO water transmission coefficient

Forward Osmosis (FO) usually has a measured water flux (Jw,exp) much smaller than its theoretical water flux (Jw,theoretical); the discrepancy between Jw,exp and Jw,th increases at a higher theoretical osmotic pressure difference (Δπtheoretical). Such discrepancy has been explained by concentration polarization (CP) and membrane resistance, together with an osmotic reflection coefficient (σ). However, it is not clear how to link the discrepancy or σ with FO performance and process optimization in different FO systems. In this study, a FO water transmission coefficient was defined as ηWT = Jw,exp/Jw,theoretical. The procedure was developed for determining ηWT and A (water permeability coefficient) with a static FO system. Results showed the relationship between ηWT and bulk solution concentration difference as per log ηWT = a•log(CDB − CFB) + b for different FO systems. This study also evaluated the difference between σ and ηWT.

Effect of surface energy of solid surfaces on the micro- and macroscopic properties of adsorbed BSA and lysozyme

The surface energy, a macroscopic property, depends on the chemical functionality and micro- and macroscopic roughness of the surface. The adsorption of two widely used proteins bovine serum albumin (BSA) and lysozyme on surfaces of four different chemical functionalities were done to find out the interrelation between macroscopic and microscopic properties. We have observed the secondary structure of protein after its adsorption. In addition, we observed the variation of surface energy of proteins due to variation in adsorption time, change in protein concentration and effect of a mixture of proteins.Surfaces of three different chemical functionalities namely, amine, hydroxyl and octyl were obtained through self-assembled monolayer on silica surfaces and were tested for responses towards adsorption of lysozyme and BSA. The adsorbed lysozyme has higher surface energy than the adsorbed BSA on amine and octyl surfaces. On hydroxyl functional surface, the surface energy due to the adsorbed lysozyme or BSA increases slowly with time.The surface energy of the adsorbed protein increases gradually with increasing protein concentration on hydrophobic surfaces. On hydrophilic surfaces, with increasing BSA concentration in bulk solution, the surface energy of the adsorbed protein on GPTMS and amine surfaces is maximum at 1μM concentration. During the adsorption from a mixture of BSA and lysozyme on octyl surface, first lysozyme adsorbs and subsequent BSA adsorption leads to a high surface energy.

Electrochemically Induced Formation of Cytochrome c Oligomers at Soft Interfaces

AbstractThe formation of cytochrome c oligomers was induced at liquid−gel and liquid−liquid interfaces via electroadsorption. At an optimum interfacial potential (Eads=0.975 V), the protein was accumulated at these soft interfaces. It was found that as the concentration of adsorbed protein increased, a single voltammetric peak evolved into double and triple peaks (tads=300 s). Analysis of the protein that accumulated at the interfaces by polyacrylamide gel electrophoresis indicated the presence of oligomeric species, corresponding to dimers (ca. 27 kD), trimers (ca. 35 kD), and even larger species (&gt;250 kD) after prolonged electroadsorption (tads=2 h) at macro‐scale soft interfaces. Accordingly, it was possible to electrochemically induce oligomerisation at these soft interfaces, which can be tuned through experimental factors such as interfacial potential difference, electroadsorption time, and bulk solution concentration. These results suggest the use of electrochemistry at soft interfaces as a strategy for the investigation of protein oligomerisation and its inhibition.

Dissolution Kinetics of Pure Zinc: The Effect of Bulk Solution Concentration and Temperature Studied by the Lead-In Pencil Electrode Technique

The lead-in pencil electrode technique was employed to study the dissolution kinetics of pure zinc in 0.01 M to 1.0 M perchlorate solution from 20–50°C. The limiting current density (ilim) during diffusion controlled dissolution and the transition potential (ET) between diffusion controlled and activation/ohmic controlled dissolution were measured. It was found that both ilim and ET decrease with decreasing bulk solution concentration, while the degree of supersaturation required for salt precipitation remained nearly constant. Increasing temperature increased the ilim and ET, whereas, the degree of supersaturation decreased with temperature. A model for anodic dissolution kinetics within the pit was used to interpret the effect of bulk solution concentration and temperature on ET. It was shown that for a constant temperature, resistance overpotential inside the pit governs the dissolution kinetics at various perchlorate concentrations, while the contribution of the corrosion potential for saturated pit solution and the IR drop within the pit determine the overall ET value at different temperatures.

Study to Define Frequency in Routine Analytical Controls in the Radiolabelling Process

In the radiolabelling process, the frequency of routine analytical testing must be defined with a risk assessment based on different factors (Pharmeuropa Vol. 26 No. 2, 5.19). Aim of this study is to define the criteria based on the risk assessment required for setting the frequency of analytical controls. 331 preparations of three different radiopharmaceuticals labeled with 99mTc were examined analyzing temporal trends of radiochemical purity values, potential correlation between radiochemical purity values and total radioactivity content of bulk as well as potential correlation between radiochemical purity values and radioactivity concentration of bulk. The analysis shows no direct correlation between percentage of radiochemical purity and total radioactivity content of preparation and between radiochemical purity values and radioactivity concentration in final bulk solution. Moreover, the routine analytical controls executed for one year on each preparation made it possible to determine how the analytical values do not have inter-operator dependency and there is no evidence of specific temporal trends over time. The study is aimed to assess any eventual criticality related with radiochemical purity tests, determine the possibility of a parametric release and the optimal frequency of tests, without reducing the level of safety of the preparations. This will produce a substantial reduction of costs and of radiation exposure to ionizing radiation of the staff dedicated to Quality Control procedures.

Dynamic modelling of pectin extraction describing yield and functional characteristics

A dynamic model of pectin extraction is proposed that describes pectin yield, degree of esterification and intrinsic viscosity. The dynamic model is one dimensional in the peel geometry and includes mass transport of pectin by diffusion and reaction kinetics of hydrolysis, degradation and de-esterification. The model takes into account the effects of the process conditions such as temperature and acid concentration on extraction kinetics. It is shown that the model describes pectin bulk solution concentration, degree of esterification and intrinsic viscosity in pilot scale extractions from lime peel at different temperatures (60 °C, 70 °C, 80 °C) and pH (1.5, 2.3, 3.1) values.

Simultaneous Surface-Near and Solution Fluorescence Correlation Spectroscopy.

We report the first simultaneous measurement of surface-confined and solution fluorescence correlation spectroscopy (FCS). We use an optical configuration for tightly focused excitation and separate detection of light emitted below (undercritical angle fluorescence, UAF) and above (supercritical angle fluorescence, SAF) the critical angle of total internal reflection of the coverslip/sample interface. This creates two laterally coincident detection volumes which differ in their axial extent. While detection of far-field UAF emission producesa standard confocal volume, near-field-mediated SAF produces a highly surface-confined detection volume at the coverslip/sample interface which extends only ~200 nm into the sample. A characterization of the two detection volumes by FCS of free diffusion is presented and compared with analytical models and simulations. The presented FCS technique allows to determine bulk solution concentrations and surface-near concentrations at the same time.