Static exclusion methods

In the case of slowly equilibrating systems, the static exclusion methods are obviously preferable to the dynamic ones. Deviations of actual elution volumes of reactants fron the presumed ones may indicate the adsorption effects of the support. 

The practice In the chromatographic analysis of porous solids 1s Identical to the ordinary column calibration procedure using a series of fully characterized standard polymers. In fact, many of the works cited above aimed at the evaluation of the packing materials for SEC. The disadvantage of the SEC method Is that It cannot be applied to those materials unsuitable for packing in a chromatography column. Gel materials of fibrous or bulky form, or of insufficient rigidity, cannot form a stable gel bed In a column, and only the static solute exclusion method can be applied to these materials. 

Size exclusion chromatography coupled to static light scattering (SEC-MALLs) Molecular weight, molecular weight distribution. Polydispersity. Radius of gyration and distribution solution conformation and flexibility. Method of choice for moleciflar weight work. [4]... 

As mentioned above, two experimental methods were examined as a source of kinetic samples Method A Agitated Glass Ampoule and Method B Static Mixer. These are described in turn in the following paragraphs. Analysis of samples was done using high temperature size exclusion chromatography (SEC) under conditions previously described (9.101. 

The experimental techniques for the study of conformational branched properties in solution are the same as used for linear chains. These are, in particular, static and dynamic light scattering, small angle X-ray (SAXS) and small angle neutron (SANS) scattering methods, and common capillary viscometry. These methods are supported by osmotic pressure measurements and, nowadays extensively applied, size exclusion chromatography (SEC) in on-line combination with several detectors. These measurements result in a list of molecular parameters which are given in Table 1. 

The many methods available for the measurement of surface and interfacial tensions can be classified as static, detachment and dynamic, the last of these being used to study relatively short time effects. Static methods usually offer a greater potential for accurate measurement than detachment methods (especially when solutions of surface-active agents are involved)43, but detachment methods tend to be the more convenient to operate. With careful experimentation and exclusion of contaminants (especially surfactants), it is usually possible to measure surface tensions to an accuracy of 0.01 to 0.1 mN m-1. It is unwise to use water which has been in contact with ion-exchange resins. 

The method of solvent exclusion has been used to explore issues of accessibility on a somewhat larger scale. An approach pioneered by Stone and Scallan and Stone et relied on static measurement using a series of oligomeric sugars and dextrans of increasing size to establish the distribution of pore sizes in different preparations of a variety of native celluloses. 

Electrical breakdown of very thin oil films is a basic difficulty in the capacitance method also. The other difficulties associated with applying static calibration to a dynamically generated film are chiefly manipulative exclusion of or compensation for stray capacities, balancing the capacitance bridge, etc. 

Prior to the evaluation of solubility and partition data of various solutes, the partition systems and the relevant parameters need to be defined. In the static equilibrium experiments, the notation, solvent (C°)/gel (Cg), refers to the transfer of a solute from the static solvent phase to the gel phase, C° and Cg indicating the molar equilibrium concentrations of the solute in the two phases. When the equilibrium experiment is performed at the saturation of the solute, C° and Cg refer to the solubilities in the external solvent and in the gel phase, respectively. In the gel chromatographic system, mobile phase (C jj)/ gel (Cg, Kgy) refers to the transfer of a solute from the mobile phase to the gel phase, C and Cg indicating the equilibrium molar concentrations of the solute in the two phases, which are correlated each other by Cg/Cuj = The notation, mobile phase (Cjjj)/gel (C°, K° )i applies to the ideal chromatographic transfer process where the distribution coefficient (K° ) Is determined solely by the steric exclusion effect of the gel matrices without any differential interactions of the solute with the two phases. The experimental determination of is subject to some uncertainty as it is difficult to establish such an ideal condition. By inclusion of urea (ref. 40,41,73) and methanol (ref. 41) in the eluents effects other than the purely steric can largely be eliminated, but there is no direct method to confirm the absence of additional gel-solute interactions. This will be further examined later. All the transfer parameters given below are the apparent quantities evaluated using the observed molar concentration data. 

Fig. 2 Solute exclusion curves (static method) for water-swollen cellulosic materials determined with dextran-oligosaccharide series. Solid line never-dried samples. Broken line dried and reswollen samples. Abscissa stands for the Stokes diameter of polymers on the logarithmic scale (molecular weight is indicated on the top line), and ordinate the amount of water inaccessible to the solute divided by the dry weight of gel. (Reproduced from ref. 18 with permission.)...

Usually, the kinetic control of the exclusion processes can be detected rather easily by varying the flow rate (dynamic methods) or equilibration times (static methods). In cases where the flow rate does not affect the chromatography the temperature dependence of the binding constant (K) on the absolute temperature (T) is given by the Van t Hoff equation... 

---