Membrane dialysis

Illustration of a dialysis membrane in action. In (a) the sample solution is placed in the dialysis tube and submerged in the solvent, (b) Smaller particles pass through the membrane, but larger particles remain within the dialysis tube. 

In one version of the urea electrode, shown in Figure 11.16, an NH3 electrode is modified by adding a dialysis membrane that physically traps a pH 7.0 buffered solution of urease between the dialysis membrane and the gas-permeable... 

Directions are provided for constructing and characterizing an ammonium ion-selective electrode. The electrode is then modified to respond to urea by adding a few milligrams of urease and covering with a section of dialysis membrane. Directions for determining urea in serum also are provided. 

Other patents (81,82) coveted the preparation of cellulose solutions using NMMO and speculated about their use as dialysis membranes, food casings (sausage skins), fibers, films, paper coatings, and nonwoven binders. NMMO emerged as the best of the amine oxides, and its commercial potential was demonstrated by American Enka (83,84). Others (85) have studied the cellulose-NMMO system in depth one paper indicates that further strength increases can be obtained by adding ammonium chloride or calcium chloride to the dope (86). 

Wet spinning of this type of hoUow fiber is a weU-developed technology, especiaUy in the preparation of dialysis membranes for use in artificial kidneys. Systems that spin more than 100 fibers simultaneously on an around-the-clock basis are in operation. Wet-spun fibers are also used widely in ultrafiltration appUcations, in which the feed solution is forced down the bore of the fiber. Nitto, Asahi, Microgon, and Romicon aU produce this type of fiber, generaUy with diameters of 1—3 mm. 

Practical appHcations have been reported for PVP/ceUulosics (108,119,120) and PVP/polysulfones (121,122) in membrane separation technology, eg, in the manufacture of dialysis membranes. Electrically conductive polymers of polyaruline are rendered more soluble and hence easier to process by complexation with PVP (123). Addition of small amounts of PVP to nylon 66 and 610 causes significant morphological changes, resulting in fewer but more regular spherulites (124). 

Fig. 5. Scanning electron micrographs of hoUow fiber dialysis membranes. Membranes in left panels are prepared from regenerated cellulose (Cuprophan) and those on the right from a copolymer of polyacrylonitrile. The ceUulosic materials are hydrogels and the synthetic thermoplastic forms a microreticulated open cell foam with a tight skin on the inner wall. Pictures at top are membrane cross sections those below are of the wall region. Dimensions as indicated.

FIGt 22-48 Transport mechanisms for separation membranes a) Viscous flow, used in UF and MF. No separation achieved in RO, NF, ED, GAS, or PY (h) Knudsen flow used in some gas membranes. Pore diameter < mean free path, (c) Ultramicroporoiis membrane—precise pore diameter used in gas separation, (d) Solution-diffusion used in gas, RO, PY Molecule dissolves in the membrane and diffuses through. Not shown Electro-dialysis membranes and metallic membranes for hydrogen. 

Dialysis. If a solution containing colloidal particle is placed on one side of a dialysis membrane, the water on the other side will allow the solution to be reduced in concentration as it passes through the membrane. 

Schulman G. Hakim R. Arias R, Silverberg M, Kaplan AP. Arbeit L Bradykinin generation by dialysis membranes possible role in anaphylactic reaction. J Am Soc Nephrol 1993 3 1563-1569. 

Hollow fiber reactors [7] and dialysis reactors [8] avoid shear stress by separating cells and flowing media. In both reactors nutrient supply takes place by diffusion through the capillary wall or the dialysis membrane. 

The cross-linking method relies on bifimctional reagents to form intermolecular linkages between the enzyme molecules to render them insoluble. Often albumin is added as an extender and glutaraldehyde is most commonly employed. This material can then be either formed as a free standing membrane or applied to the inner surface of the dialysis membrane... 

With either type of dialysis, studies suggest that recovery of renal function is decreased in ARF patients who undergo dialysis compared with those not requiring dialysis. Decreased recovery of renal function may be due to hemodialysis-induced hypotension causing additional ischemic injury to the kidney. Also, exposure of a patient s blood to bioincompatible dialysis membranes (cuprophane or cellulose acetate) results in complement and leukocyte activation which can lead to neutrophil infiltration into the kidney and release of vasoconstrictive substances that can prolong renal dysfunction.26 Synthetic membranes composed of substances such as polysulfone, polyacrylonitrile, and polymethylmethacrylate are considered to be more biocompatible and would be less likely to activate complement. Synthetic membranes are generally more expensive than cellulose-based membranes. Several recent meta-analyses found no difference in mortality between biocompatible and bioincompatible membranes. Whether biocompatible membranes lead to better patient outcomes continues to be debated. 

Flow injection analysis (FIA) (Ruzicka and Hansen), since 1975 In continuous flow, stopped flow or with merging zones (FIA scanning or intermittent pumping) Adapted voltammetric electrodes Membranes for Partial dialysis Membrane amperometry (Clark) Differential techniques (Donnan) Computerization, including microprocessors Special measuring requirements in plant control (to avoid voltage leakage, etc., Section 5.5)... 

H Yasuda, A Peterlin, CK Colton, KA Smith, EW Merrill. Permeability of solutes through hydrated polymer membranes HI. Theoretical background for the selectivity of dialysis membranes. Makromol Chem 126 177-186, 1969. 

Materials. Deionized-distilled water was used for all syntheses and distilled water was used in all solutions. All salts were reagent grade and were used as received. Dialysis membrane was Spectrapor no. 2, 12,000 upper molecular-weight-cutoff membrane from Spectrum Medical Industries, Los Angeles, CA. 

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