Molecular weight calibration

The molecular weight data were obtained from integrating SEC traces between 15.5 and 26.1 min (i.e., monomer peak was excluded), and calibrated on the basis of polystyrene standards (the calibrated molecular weight of starter sequences 60 and 66 is ca. 1.5 kDa the molecular weights of polymers were underestimated). 

The practical significance of the result of this example lies in the great ease with which viscosity measurements can be made. Once the k and a values for an experimental system have been established by an appropriate calibration, molecular weights may readily be determined for unknowns measured under the same conditions. Extensive tabulations of Mark-Houwink coefficients are available, so the calibration is often unnecessary for well-characterized polymers (see Table 4.5). 

The duplicate gel will be used to calibrate molecular weights and visualize total protein. 

Mr describes the apparent molecular mass of a protein. That means the position on a calibrated molecular weight... 

Stacy in 1985 was able to determine molecular weights of PPS by light scattering of solutions above 200 C and used the values to calibrate molecular weight distributions determined by gel permeation chromatography above 200°C. Heterogeneity index (M /M ) for PPS is near 1.7, less than the value of 2.0 expected of condensation polymers. The difference is the absence of a low molecular weight tail in PPS. 

Absolute and Pullulan-Calibrated Molecular Weights and 2R for Studied Proteins... 

Mean time between failure Multivariate analysis Multivariate calibration Molecular weight Molecular weight distribution... 

The viscosity average molecular weight is not an absolute value, but a relative molecular weight based on prior calibration with known molecular weights for the same polymer-solvent-temperature conditions. The parameter a depends on all three of these it is called the Mark-Houwink exponent, and tables of experimental values are available for different systems. 

Since viscometer drainage times are typically on the order of a few hundred seconds, intrinsic viscosity experiments provide a rapid method for evaluating the molecular weight of a polymer. A limitation of the method is that the Mark-Houwink coefficients must be established for the particular system under consideration by calibration with samples of known molecular weight. The speed with which intrinsic viscosity determinations can be made offsets the need for prior calibration, especially when a particular polymer is going to be characterized routinely by this method. 

To circumvent this need for calibration as well as to better understand the separation process itself, considerable effort has been directed toward developing the theoretical basis for the separation of molecules in terms of their size. Although partially successful, there are enough complications in the theoretical approach that calibration is still the safest procedure. If a calibration plot such as Fig. 9.14 is available and a detector output indicates a polymer emerging from the column at a particular value of Vj, then the molecular weight of that polymer is readily determined from the calibration, as indicated in Fig. 9.14. 

Polydisperse polymers do not yield sharp peaks in the detector output as indicated in Fig. 9.14. Instead, broad bands are produced which reflect the polydispersity of synthetic polymers. Assuming that suitable calibration data are available, we can construct molecular weight distributions from this kind of experimental data. An indication of how this is done is provided in the following example. 

Both preparative and analytical GPC were employed to analyze a standard (NBS 706) polystyrene sample. Fractions were collected from the preparative column, the solvent was evaporated away, and the weight of each polymer fraction was obtained. The molecular weights of each fraction were obtained usmg an analytical gel permeation chromatograph calibrated in terms of both and M. The following data were obtained ... 

The main problem of determination of molecular weight distribution (MWD) of dextrans (polysachaiides which ai e used as active substances for infusion medicines) is low robustness of the existing method. It means that obtained results are strongly dependent on controlled and uncontrolled pai ameters of chromatographic system standai d substances for calibration loading on columns etc. It has been shoved on practical examples. 

Such data can provide a calibration curve and allow the constants (E) and F ) in equation (20) to be determined. The value of the molecular weight of an unknown solute can then be obtained from its (H) value by reading the value directly from the curve or by calculation using the predetermined constants (E) and (F ) in equation (20). It should be pointed out that an error of up to 30% may not appear to be very useful but, in fact, such precision can be extremely valuable in the preliminary examination of many biochemical substances where only very small quantities of material are available. It is also an ideal method for molecular weight determination before more accurate, labor-intensive and time-consuming methods are considered. 

Calibrate the system. Use narrowly dispersed molecular weight standards of the polymer of interest to construct a calibration curve of log molecular weight versus elution volume (Eig. 3.2). If a more sophisticated software system is available, a broad molecular weight standard may be used to calibrate the system. 

Linear type columns are especially designed to have wider linear molecular weight ranges. These linear-type columns are highly recommended for correcting nonlinear sections of molecular weight calibration curves (Table 6.2). 

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