Solution depletion

The solution depletion method for studies of adsorption in solution uses material in the form of powder or pellets with specific dimensions and surface areas. This material may be physically or chemically treated to produce hydrophobic, or positively or negatively charged hydrophilic surfaces which is exposed to the solution. The decrease in concentration of the adsorbate from the bulk solution is then measured. The precision of this method is dependent on the analytical technique used. However, for biological material, the technique does not allow measurement of subtle changes in surface denaturation. The technique has been used by a number of researchers.  

Adsorption isotherms of jff-lactoglobulin on polystyrene latex particles were studied by Mackie et al for pH values of 4.65,12, and 9.0. The latex and attached protein were then removed by centrifugation, and the concentration of protein remaining in solution was calculated by assaying the supernatant by the Lowry method. 

Kim and Lund used solution depletion techniques to study the adsorption of jff-lactoglobulin on nonporous stainless steel particles with an average diameter of 25.5 //m. They found that a monolayer adsorbed very tightly to the stainless steel surface and that a significant fraction of the protein was irreversibly adsorbed. 

Adsorption of BSA was examined by Muramatsu and Kondo on positively and negatively charged microcapsules. The overall adsorption profiles were governed by the sign of the net charge of the protein and the adsorbent. The amount of adsorption was smallest on the surface that had an isoelectric point similar to that of BSA. Thus, the charge balance was assumed to play a role in the adsorption and the molecular structure of BSA. The technique lends itself very nicely to a variety of surfaces. 

Scanning I inneling Microscopy (STM) and Atomic Force Microscopy (AFM) 

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Measurements of the adsorption of inhibitors on corroding metals are best carried out using the direct methods of radio-tracer detection and solution depletion measurements . These methods provide unambiguous information on uptake, whereas the corrosion reactions may interfere with the indirect methods of adsorption determination, such as double layer capacity measurements", coulometry", ellipsometry and reflectivity Nevertheless, double layer capacity measurements have been widely used for the determination of inhibitor adsorption on corroding metals, with apparently consistent results, though the interpretation may not be straightforward in some cases. 

The cellular reaction product consisted of alternating plates of C03W lamellae in a solute-depleted Co matrix (eCo). Ffomogenized ingots were cut into slices 1 mm thick and then heat-treated. Spark erosion was used to trepan 3 mm diameter discs which were then jet electropolished to form thin foils for TEM examination in a Philips EM 430 STEM instrument operating at 300 kV in the nanoprobe mode with a probe size of 5 to 10 nm. 

In equation (34), n is the number of cells and Na is Avogadro s number, and Rt is the total carrier concentration (including both bound and free carriers). Solute depletion can be especially important in laboratory experiments, since large numbers of cells are generally employed at low solute concentrations that are typical of trace elements in natural waters. On the other hand, at high solute concentrations corresponding with carrier saturation, nonspecific adsorption to membrane components other than the carriers becomes important, and thus interpretation is much more difficult. 

The left-hand side of the above equation gives the Ilkovic expression. It is thus possible to consider the right-hand side as correction terms to the Ilkovib equation. These corrections must take into account spherical diffusion, solution depletion in the neighbourhood of the drop due to previous drops, contact area with and shielding due to the capillary, and solution stirring. 

In the case of adsorbents with high surface area, changes in protein bulk solution concentration before and after adsorption are usually large enough for independent determination of the amount of protein adsorbed, either via solution depletion meas-... 

The fact that silanol persistence can be favored by equilibrium conditions rather than control of condensation kinetics by steric or electronic factors is usually not considered. The phase separation which results from highly condensed systems continuously removes material from deposition solutions, depleting soluble silane species. While condensed silanols or siloxanes are typically not regarded as participating in a reversible reaction with water or alcohol, they do indeed participate in an equilibrium reaction. Iler [16] has shown that even hydrated amorphous silicon dioxide has an equilibrium solubility in methanol, which implies the formation of soluble low molecular... 

Adsorption isotherms were measured by the solution depletion technique. Enzyme solutions were equilibrated with powdered quartz for varying lengths of time. The solid was removed by centrifugation and the supernatants were analyzed. Total protein content of the solutions, before and after equilibration with the quartz, was measured via absorbance at 280 nm and the difference calculated as adsorbed protein. All adsorption isotherms were measured at 25.0°C in Tris buffer (0.1M Tris[hydroxymethyl]aminomethane and 10 mM CaCl2 adjusted to pH 8.6 with HCl). 

Mass-transport limitations are common to all processes involving mass transfer at interfaces, and membranes are not an exception. This problem can be extremely important both for situations where the transport of solvent through the membrane is faster and preferential when compared with the transport of solute(s) - which happens with membrane filtration processes such as microfiltration and ultrafiltration - as well as with processes where the flux of solute(s) is preferential, as happens in organophilic pervaporation. In the first case, the concentration of solute builds up near the membrane interface, while in the second case a depletion of solute occurs. In both situations the performance of the system is affected negatively (1) solute accumulation leads, ultimately, to a loss of selectivity for solute rejection, promotes conditions for membrane fouling and local increase of osmotic pressure difference, which impacts on solvent flux (2) solute depletion at the membrane surface diminishes the driving force for solute transport, which impacts on solute flux and, ultimately, on the overall process selectivity towards the transport of that specific solute. 

A number of variations of the basic DME have been devised. The vertical-orific capillary, formed by bending a capillary into a right angle and cutting off the capillary near the bend, is claimed to eliminate problems of current maxima and depletion effects (growth of a drop in a solution depleted of electroactive material by the preceding drop), and to provide greater uniformity... 

Much of the early studies of surfactant adsorption at the solid-solution interface were based on classical experimental techniques, such as solution depletion [1, 32], fluorescence spectroscopy [2], and measurements of the differential enthalpy of adsorption [2], Such methods have provided much of the basic initial understanding. However, they provide no direct structural information and are difficult to apply to mixtures [23, 34], However, when combined with other techniques, such as NMR and flow microcalorimetry, they provide some insight into the behaviour of mixtures. This was demonstrated by Thibaut et al. [33] on SDS/C10E5 mixtures adsorbed onto silica and by Colombie et al. [34] on the adsorption of SLS/Triton X-405 mixtures onto polystyrene particles. 

If W is the quantity of solvent and the concentration of the solute is expressed as C on a solute-free basis, the solute depletion can be expressed as W Co - C). An increase in the mass of seed crystals accrued during growth is equal to the mass of crystals m at time t, less the mass of seeds iih. This can be expressed as ... 

In a variemt, known as thin layer wicking, the ascent or descent of the liquid is measured through a packed thin layer, supported on a glass microscopic slide. Constanzo et al. showed that for a number of model systems this method give results for cos a agreeing with those obtained from direct measurements on a deposited and dried lawn. We repeat the caveat that the dynamic methods fall when for surfactant solutions, depletion takes place. 

The work discussed in this section clearly delineates the role of droplet size distribution and coalescence and breakage phenomena in mass transfer with reaction. The population balance equations are shown to be applicable to these problems. However, as the models attempt to be more inclusive, meaningful solutions through these formulations become more elusive. For example, no work exists employing the population balance equations which accounts for the simultaneous affects of coalescence and breakage and size distribution on solute depletion in the dispersed phase when mass transfer accompanied by second-order reaction occurs in a continuous-flow vessel. Nevertheless, the population balance equation approach provides a rational framework to permit analysis of the importance of these individual phenomena. 

It is observed, even in the partial solution to the problem, that realistic models of the droplet coalescence and breakage processes as discussed in Section V,D,2 have yet to be employed. A parallel development has occurred. The work is currently at the point where the realistic model of the droplet dynamics can be applied to the pertinent problems of extent of reaction and solute depletion in dispersions. The success of this effort would permit the researcher and designer to predict dispersed-phase reactor performance from fundamental properties of the dispersion, operation conditions of the vessel, and knowledge of the intrinsic kinetics. 

On an industrial scale, emphasis is put on good solute depletion and liquid-liquid extraction is, therefore, carried out in several stages. 

Other considerations in homogeneous nucleation relate to surface stresses in small crystals and to the effect of solute depletion in the immediate neighborhood of fonuing aggregates. 

Figure 4-6 A schematic representation of the solution depletion in the vicinity of the aggregate being formed (the density of lines represents the concentration of solution).

Adsorption isotherms are habitually obtained using the solution depletion method, which consists of comparing the solute concentrations before and after the attainment of adsorption equilibrium. Electrokinetic or zeta potentials are determined by two techniques microelectrophoresis [12,14,17] and streaming potential [13,58,59]. The former is employed to measure the mobility of small particles of chemically pure adsorbents, whereas the latter is adopted to investigate the electrophoretic behaviour of less pure coarser mineral particles. A correlation between the adsorption and electrophoretic results is usually examined with the aim of sheding light on the mechanism by means of which the surfactants are adsorbed at the solution-solid interface. This implies the necessity of maintaining the same experimental conditions in both experiments. For this purpose, the same initial operational procedure is applied. 

Porocrit process is very effective at removing the flavor components, as judged by the listed solute depletion data given in the last column of Table 5. 

If the solute-depleted solid solution adjacent to the grain-boundary precipitate is anodic, and the cathodic reaction is supported by the pre-... 

Fig. 7.52 Interface profile of intergranular corrosion when solute-depleted zone is anodic to precipitate and undepleted matrix, (a) Intergranular attack when precipitateand solute-depleted zone iscontinuous. (b) Intergranular attack when precipitate and depleted zones are discontinuous...

Methods. The diffusion experiments were performed at room temperature (23 C) utilizing a glass diffusion cell consisting of two compartments each with a volume of 175 ml. Each chamber was stirred at a constant rate to reduce boundary layer effects. Solute concentrations were monitored by h or C tracers, refractive index, or U.V. spectroscopy. Partition coefficients, defined as the ratio of the concentrations in the membrane and in the bulk aqueous phase were determined by solution depletion technique. 

Protein solution depletion via adsorption on finely divided substrates is quantitative, but applicability to low surface area materials of biomedical relevance is often minimal. Adsorption of radiolabeled macromolecules is... 

Spike standard solution, enriched minor Isotope A Spike standard solution, depleted major isotope B Natural standard solution, minor Isotope A Natural standard solution, major isotope B... 

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