Diffusion dialyzer

FIGURE 5A.2 A dialysis experiment. The solution of macromolecules to be dialyzed is placed in a semipermeable membrane bag, and the bag is immersed in a bathing solution. A magnetic stirrer gently mixes the solution to facilitate equilibrium of diffusible solutes between the dialysate and the solution contained in the bag. 

The permeability tests for alkali metal ions in the aqueous solution were also conducted. When an aqueous salt solution moves to cell 2 through the membrane from cell 1, the apparent diffusion coefficient of the salt D can be deduced from a relationship among the cell volumes Vj and V2, the solution concentration cx and c2, the thickness of membrane, and time t6 . In Table 12, permeabilities of potassium chloride and sodium chloride through the 67 membrane prepared by the casting polymerization technique from the monomer solution in THF or DMSO are compared with each other and with that the permeability through Visking dialyzer tubing. The... 

Ratio of apparent diffusion coefficient of 67 membrane to the cellulosic membrane. Visking dialyzer tubing. 

Three primary processes are utilized for the removal of substances from the blood. Diffusion is the movement of a solute across the dialyzer membrane from an area of higher concentration (usually the blood) to a lower concentration (usually the dialysate). This process is the primary means for small molecules to be removed from the bloodstream, such as electrolytes. At times, solutes can be added to the dialysate that are diffused into the bloodstream. Changing the composition of the dialysate allows for control of the amount of electrolytes... 

Figure 8.1 shows, in graphical terms, the concentration gradients of a diffusing solute in the close vicinity and inside of the dialyzer membrane. As discussed in Chapter 6, the sharp concentration gradients in liquids close to the surfaces of the membrane are caused by the hquid film resistances. The solute concentration within the membrane depends on the solubility of the solute in the membrane, or in the liquid in the minute pores of the membrane. The overall mass transfer flux of the solute J(kmol h m" ) is given as... 

As an artificial dialyzer is not used in peritoneal dialysis, use of the term artificial kidney might not be appropriate in this case. In peritoneal dialysis,the dialysate solution is infused into the peritoneal cavity of the patient and later discharged. Uremic toxins in the blood are removed as the blood flows through the capillaries in the peritoneum to the dialysate by diffusion. Water is removed by adding glucose to the dialysate, thereby making the osmolarity of dialysate higher than that of the blood. 

While both of these devices use hollow fiber membranes similar to the primary components of kidney dialyzer units, the difference between the two techniques lies in how the analyte undergoes mass transport into the device. Microdialysis sampling is a diffusion-based separation process that requires the analyte to freely diffuse from the tissue space into the membrane inner lumen in order to be collected by the perfusion fluid that passes through the inner lumen of the fiber. Ultrafiltration pulls sample fluid into the fiber lumen by applying a vacuum to the membrane (Figure 6.1). 

It was seen that the two readily diffusible substances, glucose and urea, did not dialyze at equivalent rates and that protein binding of calcium had to be overcome to obtain a dialysis rate proportional to its concentration. The instrument usually provides a dialysis rate (and therefore an amount dialyzed) which is proportional to the concentration of the substance being tested. However, this proportionality would need to be checked for any test adapted to automatic analysis. It was also seen that dialysis was influenced by the presence of protein, salts, membrane charges, etc., in that dialysis rate from standards was not always identical with that from plasma or serum. To date these differences have been corrected for by a constant factor. 

As blood circulates along the dialyzer membrane, uremic toxins diffuse into the dialysate that is discarded, under the action of the concentration gradient (Figure 18.3). 

In these cases, substances carried by blood are removed in the dialysate phase, which is separated from blood by a semipermeable membrane, as described in Figure 18.2. Toxins should cross this barrier by diffusion, before being treated. Toxins that bind to albumin have proven refractory to removal by conventional hemodialysis. Such toxins can, however, be removed by adding binders to the dialysate that capture them after being dialyzed through the membrane. 

Microdialysis was achieved in a fused silica chip with in situ photopattemed porous membrane, as shown in Figure 5.13. Phase-separation polymerization of the membrane (7-50 pm thick) was formed between posts. The posts maximize the mechanical strength of the membrane so that it can withstand a pressure drop of 1 bar. Low MW cutoff (MWCO) membrane, which can be formed by using less organic solvent, 2-methoxyethanol, appears to be more transparent (see Figure 5.13). This low MWCO membrane can be used to dialyze away low MW molecules, such as rhodamine 560, but not fluorescently labeled proteins (insulin, BSA, anti-biotin, and lactalbumin). Fligh MWCO membrane, which was formed by more organic solvent, allows diffusion of lactalbumin [347]. 

Homstein and Crowe (37) prepared a water extract of lean beef, concentrated the extract by freeze-drying and dialyzed the solution at 0°C against an equal volume of water. The dialysis procedure was repeated several times and the combined diffusates were lyophilized to yield a white, fluffy powder that rapidly browned on exposure to air to give a "meaty" odor. 

Diffusate powder prepared by freeze-drying dialyzable water-soluble solutes from beef is undoubtedly the best precursor mixture for producing "meaty" odor and flavor since it is these ingredients that are largely responsible for the flavor of cooked meat. 

Dialysis A purified protein is in a Hepes (7V-(2-hydroxyethyl)piperazine-A/ -(2-ethanesulfomc acid)) buffer at pH 7 with 500 mM NaCl. A sample (1 mL) of the protein solution is placed in a tube made of dialysis membrane and dialyzed against 1 L of the same Hepes buffer with 0 mM NaCl. Small molecules and ions (such as Na+, Cl-, and Hepes) can diffuse across the dialysis membrane, but the protein cannot. 

Isolation of the myeloma protein that combines with isomaltose units of dextran was achieved by affinity chromatography, for which the pattern is shown in Fig. 28. The eluate obtained with isomaltose was collected, dialyzed, and then lyophilized. Diffusion in agar, performed by standard methods, showed that the preparation formed a precipitin with dextran (inset of Fig. 28). 

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