Water regain

On account of the relatively low water regain of cellulose acetate, the molal concentration of ionic groups in the swollen material exceeds Smmolal. This is comparable to the concentration of 300 ppm sodium chloride, a typical reverse osmosis product solution. Our homogeneous membranes are believed to be very similar to the active layer of an asymmetric membrane as developed by Loeb and Sourirajan. It is evident therefore that the concentration of fixed charges in the membrane is sufficient to exercise a significant Donnan exclusion of co-ions on the downstream side of the membranes in a reverse osmosis plant. 

Water Regain and Bed Volume Gel chromatography media are often supplied in dehydrated form and must be swollen in a solvent, usually water, before use. The weight of water taken up by 1 g of dry gel is known as the water regain. For G-50, this value is 5.0 0.3 g. This value does not include the water surrounding the gel particles, so it cannot be used as an estimate of the final volume of a packed gel column. Most commercial suppliers of gel materials provide, in addition to water regain, a bed volume value. This is the final volume taken up by 1 g of dry gel when swollen in water. For G-50, bed volume is 9 to 11 mL/g dry gel. 

Name Fractionation Range for Proteins (daltons) Water Regain (mLVg dry gel) Bed Volume (mLVg dry gel)... 

The characteristic structure of the diluent-modified SDVB copolymers is retained in their sulfonated derivatives. A comparison of the solvent regains of macroporous sulfonic acid resin, conventional sulfonic acid resin, and their parent hydrocarbon matrices is made in Table 1. The sulfonated macroporous product like its parent hydrocarbon copolymer also takes up normally incompatible solvents and the close similarity of their regains in the sulfonated material to the water regain of the hydrocarbon matrices, expressed in compatible units, shows that the macropores have largely survived the sulfonation... 

Based on simple models for screening a relation between Kd, molecular size and water regain may be derived (Porath, 1962b). 

The molecular-sieving effect on proteins has been very clearly demonstrated by Pedersen (1962). Bovine serum albumin, obtained by fractionated ammonium sulfate precipitation, was filtered through a column of cross-linked dextran of water regain 15 gm/gm (Sephadex G-200). Monomer and dimer forms were easily separated from each other and from other components of larger sedimentation constants (Fig. 8). Heterogeneity in the monomer as well as in the dimer preparation was indicated... 

Table II lists the polar amino acid content of four polyamide materials along with their corresponding water regains at 50% RH. These data suggest that insoluble proteins with polar side chains bind more water than those without (53, 54). However, the wide range of water...

P 1. Parrish, J. R. Measurement of water regain and macropore volume of ion exchange resins. J. Appl. Chem. 15, 280 (1965). 

The water content of a resin is usually expressed as a percent of its swollen weight, but some authorities prefer to express water content as the weight of water taken up by 1 gram of initially dry resin, in which case it is termed water regain. If the water content is W percent and the water regain WR (gH20 per dry gram), the relation between the two values is ... 

BOX 4.4 Simplified Measurement of Water Regain and Voids Volume... 

N.B. For more accurate determinations of water regain only, the voids water is not removed by suction but extracted by centrifuging. 

Figure 2. Oxygen Permeability in EvOH-32 as a function of water regain at 20°C (5.). ...

The water regain in the EvOH layer is calculated as a function of time using eqn 1. The initial loading of water is taken directly from the retort calculation outside humidity is imposed only on the outside of the package. The food contents are assumed to remain at 100% humidity at all times. 

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