Vapor pressure osmometry method

However, because of the high price, MALDI-TOF mass spectrometers have not come into wide use. Vapor pressure osmometry (VPO), an old and traditional method for estimating molecular weight, is useful in the field of CPO chemistry. The experimental error of this measurement is approximately 10% however, the obtained data are sufficiently useful to estimate the number of porphyrins in a molecule. 

Vapor pressure osmometry in principle, should produce valid results at moderate molalities (a few hundredths to a few mol kg-- -) but the real accuracy and precision of this method have not yet been properly demonstrated and/or documented (Goldberg, Nuttall, and Staples, 1979). 

In this work, bis-phthalonitrile networks (1, 2) were examined by dynamic mechanical and dielectric methods, supplemented with infrared measurements of state of cure, DSC, vapor pressure osmometry, and solvent extraction. For resins cured with 4,4 -methylene dianiline as co-reactant, a simple network model rationalizes the data. 

The association number of Li amides, such as LrN(SiMe3)2, organolithium compounds bound at the a-position to S or Se atoms, such as LiCH2SePh, and various transition metal complexes was determined at 0°C in THF or at —35°C in Et20, by differential vapor-pressure osmometry. The method allows handling compounds sensitive to autooxidation, moisture and temperature . ... 

Absolute methods end group analysis, membrane osmometry, vapor pressure osmometry, static light scattering, mass spectrometry, sedimentation measurements. 

Vapor Pressure Osmometry. VPO is a very practical method for determining Mn values in a wide range of solvents and temperatures. Recently, results obtained with classical pendant-drop instruments showed a significant dependence of the calibration constant upon the molecular weight of the standards (8,9). On the other hand, with an apparatus equipped with thermistors allowing the volume of the drops to be kept constant, this anomaly is not observed (10,11). 

Vapor Pressure Osmometry. Number-average molecular weights were evaluated with a vapor pressure osmometer (Knauer) following a previously described method (18). 

The close interplay of analytical methods gives much additional information especially in those areas where the analyzed substances are very complex. Thus, while ultracentrifuge analyses for petroleum (32, 33, 34) gave much information, the broad approach used by others (35, 36, 37) involved x-ray scattering, infrared, NMR, oxidation rates, GPC, MS, pyrolysis, and vapor pressure osmometry (VPO) applied to macrostructures of asphaltic fractions. Molecular complexes substantially larger than the foregoing macrostructures are difficult to characterize by methods short of ozonolysis (38) and general pyrolysis (39). 

Analysis Methods. Unless otherwise specified, the average molecular weights were obtained by vapor pressure osmometry (VPO) in benzene according to ASTM D2503. For the aromatic fractions, an average molecular weight is also obtained by H NMR and reported in the respective tables. 

Vapor-pressure osmometry values were determined by J. Humes, and the infrared method for percent hydroxyl was developed by G. Reid. The help of these persons is sincerely appreciated. 

Vapor pressure osmometry (VPO) a method for determining molecular weight. 

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. 

Small-angle neutron scattering Transmission electron microscopy Scanning probe technologies Membrane and vapor pressure osmometry Light-scattering methods Nuclear magnetic resonance... 

Recall Eqs. 2-68 and 2-78). Direct measurement of A P is difficult because of the small magnitude of the effect. (At lOg/liter concentration in benzene, a polymer with M equal to 20,000 produces a vapor pressure lowering of about 2 x 10 mm Hg at room temperature. The limits of accuracy of pressure measurements are about half this value.) It is more accurate and convenient to convert this vapor pre.ssurc difference into a temperature difference. This is accomplished in the method called vapor phase osmometry. The procedure is also known as vapor pressure osmometry or more accurately as thermoelectric differential vapor pressure lowering. 

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