Molecular weigh! determination

For quantitative analysis, the cell constant k is determined with a weighed internal standard and then used in calculating the amount of other compounds present. Starting with Equation 2, Paul and Umbreit (1) derived the following equation for molecular weight determination in a dual chromatographic system ... 

It should be noted that a LiCl solution is accepted in high pressure liquid chromatography as an excellent way of disrupting the association of molecules in order to determine their true molecular weigh. 

Based upon the molecular weigh studies il was obvious thal solutions of Grignard compounds contain dimer species. In order to determine whether the equilibrium... 

The chemical structure of the polyolefins determines their susceptibility to oxidative degradation. Linear polyethylene, in the absence of additives, is more resistant to oxidation that polypropylene that oxidizes rather readily due to the presence of labile tertiary hydrogens. It was demonstrated, for instance, that the molecular weigh of polypropylene sheets in a 138°C oven can drop from 250,000 to approximately 10,000 in 3 h [522]. The process of oxidation was shown to take place according to the following scheme [522] ... 

In conclusion, polymer hydrodynamic size estimations from intrinsic viscosity measurements can be in error because shear rate and/or concentration conditions are too high. If intrinsic viscosities are correctly measured, then a viscous average molecular weigh can be determined from the Mark-Houwink equation provided that... 

In determining the molecular weight of liquids the apparatus shown in Fig. 82 (p. 210) is convenient for weighing and transferring the liquid to the tube. 

Tlic density (p) of a substance is tlic ratio of its mass to its volume and may be expressed in units of pounds per cubic foot (Ib/ft ) or kilograms per cubic meter (kg/nv ). For solids, density can be determined easily by placing a known mass of the substance in a liquid and measuring tlie displaced volume. The density of a liquid can be measured by weighing a known volume of the liquid in a gradmitcd cylinder. For gases, tlie ideal gas law (to be discussed in Section 4.6) can be used to calculate tlie density from tlie temperature, pressure, and molecular weight of tlie gas. 

Determination of oxygen. The sample is weighed into a silver container which has been solvent-washed, dried at 400 °C and kept in a closed container to avoid oxidation. It is dropped into a reactor heated at 1060 °C, quantitative conversion of oxygen to carbon monoxide being achieved by a layer of nickel-coated carbon (see Note). The pyrolysis gases then flow into the chromatographic column (1 m long) of molecular sieves (5 x 10-8 cm) heated at 100 °C the CO is separated from N2, CH4, and H2, and is measured by a thermal conductivity detector. 

An unknown substance, X, was isolated from rabbit muscle. Its structure was determined from the following observations and experiments. Qualitative analysis showed that X was composed entirely of C, H, and 0. A weighed sample of X was completely oxidized, and the H20 and C02 produced were measured this quantitative analysis revealed that X contained 40.00% C, 6.71% H, and 53.29% O by weight. The molecular mass of X, determined by mass spectrometry, was 90.00 u (atomic mass units see Box 1-1). Infrared spectroscopy showed that X contained one double bond. X dissolved readily in water to give an acidic solution the solution demonstrated optical activity when tested in a polarimeter. 

Isotope dilution analysis permits one to determine the purity of a radiochemical. Compound X, molecular weight of 150 (specific activity 1.0 mCi/mmol), was checked for purity by carefully weighing 1.5 mg of the radiochemical and mixing with 1000 mg of unlabeled compound X and recrystallizing until a... 

The molecular weight of a moderately volatile substance can be determined by the historically important Victor Meyer procedure, by which the volume of gas produced by vaporization of a weighed sample of an unknown is measured at a given... 

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