Osmometry applications

Typically, the characterization of supramolecular systems requires the application of a whole set of analytical techniques. Without going into details, the capsular structure of the tennis ball 1-1 has been confirmed by X-ray crystallography, vapor phase osmometry (VPO), and NMR experiments.1111 The encapsulation of guests can be routinely analyzed by NMR experiments. Recently, a mass spec-trometric method was developed that not only... 

Application of the present procedure to the characterized cotton supplied by The Buckeye Cellulose Corp. gives the results shown in the lower part of Table I. The agreement among the data is particularly good, even though the value for DPn is somewhat lower than that determined by osmometry (this raises slightly the polymolecularity ratio DPw/DPn). This behavior of DPn and the ratio has been noted previously (1) and is still in accord with reports of others (10). The polymolecularity ratios for the cellulose I, II, III, and IV samples reported in the preceding paper... 

Termination can occur for polymer radicals of any size and so there is inevitably a wide distribution of sizes among the final molecules The distribution can be predicted by application of kinehc principles and can be determined experimentally by fractionadon of the whole polymer, e.g., by gel permeation chromatography. It is possible to quote only average molecular weights for polymers they can be determined by several experimental methods, e.g., osmometry and viscomedy. 

In a solution containing both unimer and micelles, Ma, which is by definition more sensitive to low molar mass particles, is always less than the weight-average molecular weight, Mv. Further details on osmometry can be found in the review by Adams (1989), whilst examples of its application to micellar block copolymer solutions are given in Chapter 3. 

The up to now most frequently used techniques as, for example, vapour pressure osmometry (VPO) or freezing point depression (with its limitation regarding the solvent dependent measuring temperature) are based upon the colligative properties of the system the classical absolute light-scattering and ultracentrifugation techniques are only occasionally and approximately applicable with respect to the determination of CMC values. Evaluation of critical micelle concentrations which are based on these latter methods suffer considerably from the insensitivity of these techniques if measurements below the CMC, i.e., below about 10-3 mol dm-3, are carried out. More sensitive methods will be discussed below. 

E> can be measured directly by membrane or vapor pressure osmometry. The application of an alternative method was described recently [64, 65]. It is based on an analysis of the sedimentation equilibrium in an analytical ul-tracentrifuge, where the solution contains the polyelectrolyte as well as a small concentration of an inert salt. In sedimentation equilibrium, the concentration gradients of both components are coupled via a Donnan-type equilibrium, which is governed by the effective charge number zeff of the polyion. Both concentration gradients can be determined in one experiment, when the polyion and the coion of the salt have sufficiently separated absorption bands in the UV or visible range. 

Zhang, W. T., M. W. Capp, J. P. Bond, C. F. Anderson, and M. T. Record, Jr. 1996. Thermodynamic characterization of interactions of native bovine serum albumin with highly excluded (glycine betaine) and moderately accumulated (urea) solutes by a novel application of v or pressure osmometry. Biochemistry. 35 10506-10516. 

Abel JE. The physical background to freezing-point osmometry and its medical-biological applications. Amer J Med Electronics 1963 2 32-41. 

For poly ether polyols an NMR method was elaborated for functionality determination [20]. The most usual and practical method for functionality determination is based on the assessment of the MW of an oligo-polyol, by a method applicable to low MW compounds (MW < 10,000 daltons), such as vapour pressure osmometry (VPO) or gel permeation chromatography (GPC), together with hydroxyl number determination. The functionality is calculated by using the fundamental equation 3.4 ... 

A special group of detectors are those which continuously measure the molar mass of sample components in the eluate. Their application allows to omit the calibration of the gel chromatographic system. So far, vapor phase osmometry for solutes with lower molar masses, and viscosity and light scattering measurements for polymers have been applied. 

Equations applicable to membrane osmometry, as also in the case of ebulliometry, cryoscopy, and vapor phase osmometry, can be rigorously derived from the second law of thermodynamics in the form... 

The field of application of Osmometry is limited to polymers with masses below 100,000, since the precision depends on the mass, and therefore it becomes inaccurate high masse Furthermore, being a colligative method, osmometry yields Mn but not Mw, and therefore it cannot be used to discriminate a narrow MMD from a broad MMD nor a unimodal MMD from a bimodal MMD. 

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