Bulk dialysis

The first fractionation of urinary ampholytes in this way was carried out by Boulanger et al. (BIO) in 1952 with the use of ion-exchange resins. They had designed this procedure previously for the fractionation of ampholytes in blood serum (B8). According to this method, deproteinized urine was subjected to a double initial procedure aiming at the separation of low-molecular weight substances from macro-molecular ones. One of the methods consisted of the fractionation of urinary constituents by means of dialysis, the second was based on the selective precipitation of urinary ampholytes with cadmium hydroxide, which, as had previously been demonstrated, permits separation of the bulk of amino acids from polypeptides precipitated under these circumstances. Three fractions, i.e., the undialyzable part of urine, the dialyzed fraction, and the so-called cadmium precipitate were analyzed subsequently. 

Problems of desorption and loss of activity encountered with natural heparin have led numerous workers to explore synthetic heparin-like polymers or heparinoids, as reviewed by Gebelein and Murphy [475, 514, 515]. The blood compatibility of 5% blended polyelectrolyte/polyfvinly alcohol) membranes was studied by Aleyamma and Sharma [516,517]. The membranes were modified with synthetic heparinoid polyelectrolytes, and surface properties (platelet adhesion, water contact angle, protein adsorption) and bulk properties such as permeability and mechanical characteristics were evaluated. The blended membrane had a lower tendency to adhere platelets than standard cellulose membranes and were useful as dialysis grade materials. 

As the pH of milk is reduced, the colloidal calcium phosphate (CCP) dissolves and is completely soluble at pH 4.9 (Chapter 5). pH adjustment, followed by dialysis against bulk milk, is a convenient and widely used technique for varying the CCP content of milk. As the concentration of CCP is reduced, the properties of the micelles are altered but they retain some of their structure even after removing 70% of the CCP. Removal of more than 70% of the CCP results in disintegration of the micelles into smaller particles (aggregates). 

The so-called Ling oxalate titration indicates that CCP consists of 80% Ca3(P04)2 and 20% CaHP04, with an overall Ca P ratio of 1.4 1 (Pyne, 1962). However, the oxalate titration procedure has been criticized because many of the assumptions made are not reliable. Pyne and McGann (1960) developed a new technique to study the composition of CCP. Milk was acidified to about pH 4.9 at 2°C, followed by exhaustive dialysis of the acidified milk against a large excess of bulk milk this procedure restored the acidified milk to normality in all respects except that CCP was not reformed. Analysis of milk and CCP-free milk (assumed to differ from milk only in respect of CCP) showed that the ratio of Ca P in CCP was 1.7 1. The difference between this value and that obtained by the oxalate titration (i.e. 1.4 1) was attributed to the presence of citrate in the CCP complex, which is not measured by the oxalate method. Pyne and McGann (1960) suggested that CCP has an apatite structure with the formula ... 

The membrane separation processes described above represent the bulk of the industrial membrane separation industry. Another process, dialysis, is not used industrially but is used on a large scale in medicine to remove toxic metabolites from blood in patients suffering from kidney failure. The first successful artificial kidney was based on cellophane (regenerated cellulose) dialysis membranes and was developed in 1945. Over the past 50 years, many changes have been made. Currently, most artificial kidneys are based on hollow-fiber membranes formed into modules having a membrane area of about 1 m2 the process is illustrated in Figure 1.7. Blood is circulated through the center of the fiber, while isotonic... 

Acidic dialysis provides tremendous purification from bacterial proteins, most of which precipitate at a pH lower than 6. However, not every recombinant protein remains soluble at acidic pH either. To test the solubility of your protein under these conditions, after at least 18-20 h of basic dialysis, transfer a small aliquot of the protein into a separate dialysis bag and put it in a precooled acidic dialysis buffer for 4-6 h, just long enough for bacterial proteins to form visible precipitation. Once the precipitate is formed, separate it by centrifugation in a table-top microcentrifuge for 5-10 min at 23,500 g. Analyze the presence of your protein in the supernatant and in the pellet by SDS-PAGE or Western blotting. If your protein is found in the supernatant, you can transfer the dialysis bag with the bulk of protein from basic dialysis conditions to acidic dialysis. 

In this system molecular weight-increased NAD (PEG-NAD, MW 20.000 Dalton) has been coentrapped within the enzyme layer behind a dialysis membrane (molecular cutoff 8.000). In the normal procedure the sensitivity for glycerol was not decreased as compared with the measurement in the presence of 2 mmol/1 (unmodified) NAD in the bulk solution. This behaviour reveals a sufficiently high reaction rate between the macromolecular NAD(H) and the enzymes GlyDH and LDH. 

Poly(s-caprolactone) Poly(e-caprolactone) is a semicrystalline polymer synthesized by anionic, cationic, free-radical, or ring-opening polymerization [94]. It is available in a range of molecular weights and degrades by bulk hydrolysis autocatalyzed by the carboxylic acid end groups. The presence of enzymes such as protease, amylase, and pancreatic lipase accelerates polymer degradation [95], The various methods of preparation of poly(e-caprolactone) nanoparticles include emulsion polymerization, interfacial deposition, emulsion-solvent evaporation, desolvation, and dialysis. These methods and various applications are extensively reviewed [94],... 

Partridge et al. (W ib) observed that when elastin from ligamentum nuchae of cattle was repeatedly extracted with 0.2. 5 M oxalic acid at 100°C the fibers completely dissolved after about 5 hr total extraction. On dialysis in cellophane only about. 5 % of the total nitrogen of the reaction mixture diffused through the membrane. The bulk of the product was a protein which was soluble in distilled water or buffer solutions at temperatures below 2f>°C, but on raising the temperature of the solution in dilute buffer at pH 4-6 a coacervate phase consisting of liquid droplets separated. The soluble material was thus similar in properties to the hemi-elastin of Horbaczewski (1882). 

Toxic anions and nonmetals are a difficult group for analysis. Some anions can be trapped in combination with a stable cation, after which the organic matrix can be destroyed, as with metals. Others can be separated from the bulk of the matrix by dialysis, after they are detected by colorimetric or chromatopathic procedures. Still others are detected and measured by ion-specific electrodes. There are no standard approaches for this group, and other than phosphorus, they are rarely encountered in an uncombined form. 

A wide variety of combinations of adsorbents were used for clean-up [34], e.g. open, gravity-fed columns, or flow controlled columns. One laboratory used a dialysis technique to separate PCDDs and PCDFs from the bulk of the fat. 

Selectivity parameters, needed for the BOHLM or BAHLM module design and their determination techniques, are analyzed. Selectivity can be controlled by adjusting the concentration, volume, and flow rate of the LM phase. Such control of the selectivity is one of the advantages of the bulk liquid membrane systems in comparison with other liquid membranes configurations and Donnan dialysis techniques. The idea of dynamic selectivity and determination techniques are presented and discussed. 

In addition to the vapor diffusion method described previously, other techniques such as the batch and micro-batch methods, bulk and micro dialysis, free interface diffusion, liquid bridge, and concentration dialysis have also been developed to produce crystals for x-ray diffraction analysis (see McPherson, 1982 and McPherson, 1999). 

The Nafion separator allows dialysis of the non-oxidizable cations to the cathode, and even though efficiency of removal is low due to the relatively high concentration of hydrogen ions, (the hydrogen ion carries the bulk of the current), the process is still economically attractive because the amounts of the unwanted cations are usually small. 

In the previous examples the membranes have been considered generally as semiperineable barriers for the separation of small molecules from bigger ones. When in parallel to the separation a chemical reaction takes place in the bulk solution or in the membrane itself, the system may be identified as a true membrane reactor. A classical example is a stirred-tank enzymatic reactor connected by a continuous recirculation loop to an ultrafiltration or dialysis unit. Such a system, when well designed, permits the continuous removal of the reaction products from the bulk solution without loss of enzyme (or the insoluble or macromolecular substrate ). 

---