Coefficient weight distribution

An important relationship exists between the weight distribution coefficient and the volume of eluant (Vmax) required to reach the maximum concentration of an eluted ion in the effluent. This is given by the equation ... 

To be absolutely correct the terms in., the brackets should be activities and not concentrations, also, two of the terms involve stationary phase activities that cannot be easily evaluated. The weight distribution coefficient for the analyte A" is designated as and is given by ... 

Compound Chemical formula Molecular weight Distribution coefficient -calc per 1E5 cm/s meas - per 1E5 cm/s... 

Another measure for the affinity of a solute ion toward the stationary phase of an ion-exchange resin is the weight distribution coefficient Dg, which is defined for an exchanged ion X- as follows ... 

Instead of the weight distribution coefficient, in most cases the capacity factor, k, is used, which is defined by Eq. (37) ... 

It follows from Eq. (37) that the capacity factor can be derived from the weight distribution coefficient. However, the determination of k from chromatographic data [see Eq. (7) in Section 2.2] is much more convenient. 

Experimentally, the weight distribution coefficient of an ion A in a given eluent is measured by equilibrating a known volume of standard solution with a known weight of resin and calculating the results from Eq. 5.7. The volume distribution coefficient, Dy, of an ion is calculated from its retention volume from a column with a given eluent ... 

To be correct the terms in the brackets should be activities and not concentrations, also, two of the terms involve stationary phase activities that cannot be easily evaluated. The weight distribution coefficient for the sample ion A is given by Da = [As ] / [Am ] and is related to the chromatographic retention factor for the sample ion by Ra = Daw / Vm, where w is the weight of stationary phase and Vm is the column hold-up volume. Substituting these terms into Eq. (4.22) after rearrangement, we have... 

Chain transfer to monomer is the main reaction controlling molecular weight and molecular weight distribution. The chain-transfer constant to monomer, C, is the ratio of the rate coefficient for transfer to monomer to that of chain propagation. This constant has a value of 6.25 x lO " at 30°C and 2.38 x 10 at 70°C and a general expression of 5.78 30°C, chain transfer to monomer happens once in every 1600 monomer... 

Selection of Solubility Data Solubility values determine the liquid rate necessaiy for complete or economic solute recoveiy and so are essential to design. Equihbrium data generally will be found in one of three forms (1) solubility data expressed either as solubility in weight or mole percent or as Heniy s-law coefficients, (2) pure-component vapor pressures, or (3) equilibrium distribution coefficients (iC values). Data for specific systems may be found in Sec. 2 additional references to sources of data are presented in this section. 

The equihbrium distribution coefficient can be calculated by material balance, using the weight of the feed F, raffinate R, and extract E, plus the weight-fraction solute in the feed xy and raffinate iv, when the weight-fraction solute in the extraction solvent y, is zero [Eq. (15-8)]. 

Solid resins have been prepared having a very closely controlled molecular weight distribution." These resins melt sharply to give low-viscosity liquids. It is possible to use larger amounts of filler with the resin with a consequent reduction in cost and coefficient of expansion, so that such resins are useful in casting operations. 

Quality assurance for size exclusion supports is based primarily on the reproducibility of molecular weight calibrations. Although the reproducibility of the exclusion and inclusion limits is important, the distribution coefficients (Ko) of included standards are a better indication of duplication. Table 10.3 (page 314) shows such data for the SynChropak GPC and CATSEC supports. 

This may be illustrated by the following example. Suppose that 50 mL of water containing 0.1 g of iodine are shaken with 25 mL of carbon tetrachloride. The distribution coefficient of iodine between water and carbon tetrachloride at the ordinary laboratory temperature is 1 /85, i.e. at equilibrium the iodine concentration in the aqueous layer is 1 /85th of that in the carbon tetrachloride layer. The weight of iodine remaining in the aqueous layer after one extraction with 25 mL, and also after three extractions with 8.33 mL of the solvent, can be calculated by application of the above formula. In the first case, if x, g of iodine remains in the 50 mL of water, its concentration is x,/50 gmL 1 the concentration in the carbon tetrachloride layer will be (0.1 —x1)/25gmL 1. 

Kd = distribution coefficient (as defined above) s/m = salt to metal ratio by weight F = fraction of equilibrium attained B = effects of side reactions... 

Keywords Complex Flexibility Molecular weight distribution Mucoadhesion Sedimentation coefficient distribution... 

Analytical ultracentrifugation (AUC) Molecular weight M, molecular weight distribution, g(M) vs. M, polydispersity, sedimentation coefficient, s, and distribution, g(s) vs. s solution conformation and flexibility. Interaction complex formation phenomena. Molecular charge No columns or membranes required [2]... 

A sedimentation coefficient distribution—either c s) versus 5 or g (s) vs. s—for a polysaccharide can also be converted into an apparent molecular weight distribution if the conformation of the polysaccharide is known or can... 

If Mark-Houwink coefficients were supplied at setup time, the chromatogram may be converted into the differential molecular weight distribution of the specimen. Various averages characterizing this molecular weight distribution are then calculated. The molecular weight distribution may be written to a file. 

Lipophilicity represents the affinity of a molecule or a moiety for a lipophilic (= fat-loving) environment and is commonly measured by the partition coefficient, (where aaa represent a generic biphasic system, e.g. oct indicates the standard octanol-water). P is valid for a single electrical species, to be specified (P for neutral forms and P for ionized species). The distribution coefficient, expressed as is a pH-dependent descriptor (Eq. 3) for ionizable solutes and results from the weighted contributions of all electrical forms present at this pH ... 

---