Gel permeation chromatography elution curves

Fig. 3-9. Gel permeation chromatography elution curve.s for anionic polystyrene standards used for calibi ation. The polystyrene standard samples were measured separately use of a mixture of polymers may cause elution volumes of very high molecular weight standards to be erroneously low [I8J.

Figure 4.20 Gel permeation chromatography elution curves for polymer standards having veiy narrow molecular weight distribution. (After Rudin, 1982.)...

The calculation of molecular weight averages from gel permeation chromatography elution curves is strai tforward by computer if the relationship between molecular weight and elution volume is known, and the results can be made rapidly available. If a column is calibrated for one polymer with narrow molecular weight standards, it may be calibrated by itoative methods for a second polymer if several - samples or just one > well-charactnized... 

Figure 3.1 (a) Distribution of molecular weights for ethylene-propylene copolymers from isospecific metallocenes (b) gel permeation chromatography elution curves for HDPE produced with CpTiPhj and Cp ZrCl mixtures. Cp = cyclo-olefins [23]... 

Fig Typical cumulative molecular-weight distribution curve for a sample of polypropylene gradient-elution data (O) and data from gel permeation chromatography. 

The chemical structure of PBS also may be altered by exposure to radiation and such changes may contribute to the solubility rate difference between an exposed and an unexposed PBS film. U-type films were prepared from unirradiated powders while IP-type films were prepared from irradiated powders. Inspection of Table II or Figure 2 shows that the three U-type films have slightly larger solubility rates than IP-type films of comparable M. The solubility rate differences between IP and U-type films are small relative to the differences between IP and IF type films. The solubility rate difference between a U and an IP film of comparable M must arise from chemical structural differences between irradiated and unirradiated powders. These radiation-induced changes may also be responsible for differences observed in the elution behavior between irradiated and unirradiated PBS samples in gel permeation chromatography experiments. Irradiated PBS samples yield abnormally broad elution curves while unirradiated samples elute normally I3.8I. 

For determining the molar mass of branched polymers gel permeation chromatography can be used. An important quantity in this connection is the hydrodynamic volume of the polymer coil, which, as shown before in Eq. (9.27), is proportional to the product [rj M. According to Benoit and co-workers (1966) the hydrodynamic volume is the key size parameter in the establishment of a universal calibration curve for gel permeation chromatography columns (see Chap. 2) if log (h/]M) is plotted versus the elution volume for a variety of polymers, the data fit a single curve. 

Gel permeation chromatography separates the sample components in a highly predictable manner. The larger molecules always elute from the column first. Also, the maximum amount of mobile phase required to elute all sample components is equivalent to one column volume. Furthermore, the elution volume of a molecule can be predicted from a calibration curve for a given set of columns. 

Fig. 4.5.6. An example of the combination of gel permeation (ion exchange) chromatography of metalloproteins with atomic absorption spectrometry for evaluation of fractions I96], Rat liver supernatant (0.2 ml) obtained after injection of cadmium chloride was applied to a TSK Gel SW 3000 column 600x21.5 mm, and eluted with 50 mM Tris-HCl buffer solution (pH 8.6 at 25°C). Absorbance at 280 nm (lower curves) and concentration of cadmium (A) or zinc (B) (upper curves) were continuously monitored. I and II indicate metallothionein-l and -II, respectively. This chromatogram indicates the contribution of ion exchange to TSK Gel SW gel-permeation chromatography, because both separated proteins have the same molecular weight, and the sequence of peaks emerging corresponds to the ion exchange chromatography separation.

The usual means of measuring molar mass distributions (MMDs) is gel permeation chromatography (GPC) which is described in Section 11.2.2.5. Denote the GPC trace as the signal G as a function of elution volume Veil it is assumed that the baseline has been subtracted. Appropriate calibration with monodis-perse standards yields the GPC calibration curve, which is the volumes at which monodisperse standards elute as a function of the molar mass M of the standard this is denoted V(A/ )... 

Gel permeation chromatography (GPC) is a convenient and reliable method to determine the entire molecular weight distribution (mwd) of a polymer. In general, the resulting elution curve D(V ), where is the elution volume is related to the mwd by Tung s integral equation... 

The molecular weight distributions of the oligomers were determined by means of gel permeation chromatography. These were done by Dr. Julian F. Johnson who was then at the Chevron Research Company. A Waters Analytical G.P.C. Model 300 was used. A combination of one 100,000 R, one 15,000 A, one 100 R, and one 45 R column was used. The columns were calibrated with normal alkanes and monodisperse polystyrenes. Samples were dissolved in toluene to obtain 60 mg/100 ml concentration they were eluted with toluene at a flow rate of 1 ml per minute at room temperature. The results were machine-computed to obtain relative molecular weights. From these, absolute values of the molecular weights were obtained by means of scaling factors calculated from experimental viscosity or vapor pressure osmometry data. The calibration curve is shown... 

The results of the gel permeation chromatography measurements by Protivova and PospisiP of the elution volumes of aromatic amines, their molecular weights, calculated molar volumes and the effective molar volumes observed and read from the calibration curves are given in Table 7.20. A comparison of the calculated and effective molar volumes revealed deviations in the behaviour of all the amines they investigated, compared to similar aliphatic hydrocarbons. 

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