Effect fractions

Estimate the effective fraction w etted packing area by Figure 9-46 or 9-43. As a general rule, try not to accept design if fraction wetted is le.ss than 0.5. If it is less, adjust tower conditions to raise value, bearing in mind that this factor is based on scattered and very incomplete data. 

It has been assumed that the total surface area of a floe is proportional to the number of singlets in that floe, a reasonable assumption for small floes and open floe structures. The effective fractional surface coverage, 0k, is not necessarily equal to the fractional surface coverage at equilibrium for a given amount of adsorbed polymer. This will be discussed in some detail below. 

Removal of viruses from the product stream can be achieved in a number of ways. The physicochemical properties of viral particles differ greatly from most proteins, ensuring that effective fractionation is automatically achieved by most chromatographic techniques. Gel-filtration chromatography, for example, effectively separates viral particles from most proteins on the basis of differences in size. 

Figure 7. Mo concentotions (o) and isotopic compositions ( ) from reducing pore fluids in Santa Monica Basin (McManus et al. 2002). Dotted line indicates seawater values for both variables. The data can be fit by a 1-D reaction-diffusion model wifli a fractionation factor of —1.005. The effective fractionation factor for Mo removal across tiie sediment-water interface is smaller, <1.0025 (see text).

An important consequence of such a model is that the effect of such sedimentary systems on the ocean Mo isotope budget is not represented by a, but rather by the relative fluxes of the isotopes across the sediment-water interface. This effective fractionation factor, is likely to be smaller than a (Bender 1990 Braudes and Devol 1997) because the diffusive zone acts as a barrier to isotope exchange with overlying waters, approximating a closed system. 

Finally, it is worth mentioning that the presence of hydration equilibria could result in effective fractional q values. This can be checked by UV- ds measurements on the Elu(III) complex as a function of temperature 12). 

If the growth front is frozen, the crystallization at the growth front depends crucially on the commensurability between the thickness of the growth front and the length of crystallizing chains. For details, see Ref. 49. A collection of polydisperse chains gets effectively fractionated at the growth front. 

With 0.5M sodium hydroxide as eluent, Sephadex G-50 effects fractionation in the molar mass range 1000-15000 dalton and can be used for a period of 3-4 weeks with a single calibration carried out with proteins and polypeptides of known molar mass, as revealed by Figure 10. Relative retention volumes 0.0 and 1.0 are defined with Blue Dextran and phenol, respectively. 

TABLE 8.1 Critical Micelle Concentration, Degree of Aggregation, and Effective Fractional Ionization for Several Surfactants With and Without Added Salt... 

This second test is especially difficult to perform and has not been perfected. This difficulty is inherent in the characteristics proper of the tannins and in their ability to bind to proteins and other macromolecules (cellulose, polyamide) used as chromatographic supports. This explains why no truly effective fractionation of flavolans has been reported. It is equally possible that the flavolans associate with each other as a function of the media conditions and that all the necessary manipulations during extraction allow some structural changes. 

Solvents differ in their capacity to effect fractionation. Thus, in a study of the polyaddition of levoglucosan, 83-90% ethanol gave a 7% yield of a fraction of Mw 22,750 and addition of one volume of acetone to the supernatant liquor gave a 7% yield of a fraction having213 Mw 38,650. Such differences in solvents may be useful, for example, in separating branched from unbranched polymers within a particular molecular-weight range. 

Ultrafiltration has been used in fractionating dextrans,244 By use of specially prepared membranes,246 it should be possible to extend this simple, gentle method to effect fractionation of polyglycoses and polysaccharides in general. Gel filtration also permits passage of macromolecules on the basis of their molecular size, and this method has proved useful in the fractionation of dextrans246 and dextrins.247 The ease and capacity of this method should make it valuable in the fractionation of polyglycoses. 

The mobile phase can be collected as a function of time at the end of the chromatographic system. The mobile phase, now called the effluent, contains the solute molecules. If the chromatographic process has been effective, fractions or cuts that are collected at different times will contain the different components of the original sample. In summary, molecules are separated because they differ in the extent to which they are distributed between the mobile phase and the stationary phase. 

Using the Alternate Protocol, all major polyphenolic compounds are separated with good resolution, which is due to the effective fractionation of acidic and neutral polypheno-... 

Thoroughly describes the effective fractionation technique of separating anthocyanins and nonan-thocyanins. 

It has been shown19,20) that under PAA complex formation with excess of partly quaternized PYP, the latter is quite effectively fractionated by composition, macromolecules of the copolymer enriched with nonalkylated units being selected in the polycomplex. It is of importance that the preliminary molecular-weight fractioned sample of P-4-VP is quarternized with ethyl bromide, i.e., under the conditions of an experiment it is possible to consider... 

In one report, the enantiomers of the racemic compound 73, whose structure resembles ketone 2a, were separated by fractional recrystallization of the optically active mandelic acid salts [43]. Although we tried to optically resolve the optically active mandelic acid salts of the racemic ketone ( )-2a, no satisfying results were obtained. After several trials, the (+)- or (-)-di-p-toluoyl tartrate salt prepared from ketone ( )-2a was effectively fractionally recrystallized and finally provided the optically active ketones (+)-2a and (-)-2a [42]. The chiral ketone (-)-2a was converted to compound 73 via compound 72 by thioacetalization followed by desulfurization using Raney nickel... 

It is to be recalled that effective fractionation is hard to achieve especially in the case of crystalline polymers. However, we also recall that special difficulties with fluorescence occur in light scattering measurements with polyacrylonitrile [see Cleland and Stockmayer (68 ) and Krigbatjm and Kotliar (750)]. 

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