Ultrafiltration molecular weight cutoff

The polyethersulfone capillary ultrafiltration membranes (Daicel Chemical Industries, Ltd., inner diameter 0.8 mm, outer diameter 1.3 mm, length 40 cm, molecular weight cutoff 150 000, water permeability 3 x 10 m m s kPa at 298 K) were used. The length and area of membrane consisting of seven hollow fibers are 40 cm and 70 cm. ... 

The retention properties of ultrafiltration membranes are expressed as Molecular Weight Cutoff (MWCO). This value refers to the approximate molecular weight (MW) of a dilute globular solute (i.e., a typical protein) which is 90% retained by the membrane. However, a molecule s shape can have a direct effect on its retention by a membrane. For example, linear molecules like DNA may find their way through pores that will retain a globular species of the same molecular weight. 

Figure 7. Association of predissociated kraft lignin sample (92% retained by nominally 500 molecular weight cutoff ultrafiltration membrane) during incubation at 160 gL 1 in 1.0 M ionic strength aqueous 0.40 M NaOH for (l)0h, (2) 50 h and (3) 480 h.

It is a key step to develop methods to separate peptides with different molecular weights. An ultrafiltration membrane system equipped with the appropriate molecular weight cutoff has been effectively used in separating peptides having desired molecular weights (Jeon et al., 2000). In order to obtain functionally active peptides, it is a common method to use the type of enzymes letting sequential enzymatic digestions. 

The transition between reverse osmosis membranes with a salt rejection of more than 95 % and molecular weight cutoffs below 50 and ultrafiltration membranes with a salt rejection of less than 10% and a molecular weight cutoff of more than 1000 is shown in Figure 2.42 [74], The very large change in the pressure-normalized flux of water that occurs as the membranes become more retentive is noteworthy. Because these are anisotropic membranes, the thickness of the separating layer is difficult to measure, but clearly the permeability of... 

The goal of most of the early work on reverse osmosis was to produce desalination membranes with sodium chloride rejections greater than 98 %. More recently membranes with lower sodium chloride rejections but much higher water permeabilities have been produced. These membranes, which fall into a transition region between pure reverse osmosis membranes and pure ultrafiltration membranes, are called loose reverse osmosis, low-pressure reverse osmosis, or more commonly, nanofiltration membranes. Typically, nanofiltration membranes have sodium chloride rejections between 20 and 80 % and molecular weight cutoffs for dissolved organic solutes of 200-1000 dalton. These properties are intermediate between reverse osmosis membranes with a salt rejection of more than 90 % and molecular weight cut-off of less than 50 and ultrafiltration membranes with a salt rejection of less than 5 %. 

A straightforward way to collect solutes from the interstitial fluid (ISF) space would be to have a semipermeable, hollow fiber, membrane-based device as originally described by Bito et al.1 Two semipermeable membrane-based devices that have been used to collect different types of analytes from various mammalian tissues include microdialysis sampling probes (catheters) and ultrafiltration probes. The heart of each of these devices is the semipermeable polymeric membrane shown in Figure 6.1. The membranes allow for collection of analytes from the ISF that are below the membrane molecular weight cutoff (MWCO). Each of these devices provides a sample that has a significantly reduced amount of protein when compared to either blood or tissue... 

The must is subsequently sterilized, boiling being the most commonly used method (McConnell and Schramm, 1995 Navratil et al., 2001 Ukpabi, 2006). Heat treatments also have the potential to alter the antioxidant capacity by changing their phenolic profiles (Wintersteen et al., 2005). However, other techniques are described in the literature. These include the use of metabisulfite (sodium or potassium salts or in commercial form as Campden tablets)—releases sulfur dioxide that either kills or inactivates most microbes (McConnell and Schramm, 1995 Roldan et al., 2011), sulfur dioxide gas (Pereira et al., 2009 Ukpabi, 2006), pasteurization (McConnell and Schramm, 1995 Mendes-Ferreira et al., 2010), and ultrafiltration, with a 50-kDa molecular weight cutoff (McConnell and Schramm, 1995). Some of these methods also promote the removal of proteins by denaturation and coagulation, resulting in more rapid clarification during maturation. 

Disposable Ultrafree-CL (Millipore) ultrafiltration cartridge units (10 kDa nominal molecular weight cutoff). 

Diafiltration is a variation of ultrafiltration, in which fresh solvent is added to the feed solution to replenish the volume ultrafiltered, and in the process washes small molecules such as salts away from the retained macromolecules. Using appropriate replenishing solutions, diafiltration is a common procedure to perform buffer exchange of proteins. Alternatively, a dilute solution may be first ultrafiltered to concentrate the feed material, then diafiltered to purify the retentate. It is sometimes possible to fractionate a mixture of macrosolutes by sequential diafiltration with a series of membranes of progressively lower molecular weight cutoff ratings. 

Table 10-4. Molecular Weight Cutoff Points of Diaflo Ultrafiltration Membranes...

UF membranes can retain macromolecules such as polysaccharides, proteins, biomolecules, polymers, and colloidal particles. Generally, ultrafiltration membranes are classified by the type of material and their nominal molecular weight cutoff (MWCO), which is usually defined as the smallest molecular weight species for which the membrane has more than 90% rejection. 

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