Molecular weight separation

TABLE 4.6 Properties and Molecular Weight Separation Ranges for TSK-GEL PW Type Packings°... 

MOLECULAR WEIGHT SEPARATION OF MACROMOLECULES BY HYDRODYNAMIC CHROMATOGRAPHY... 

Hydrodynamic chromatography (HdC) is a relatively new technique, especially in molecular weight separation. It was first investigated in 1969 by DiMarzio and Guttman (1,2) and was called separation by flow (3,4). Small started calling it hydrodynamic chromatography in 1974 (5). The application of this technique was first concerned with the separation of particle size. Prud homme applied it to the molecular weight separation of macromolecules in 1982 (6). 

Currently, there are several molecular weight separation techniques, such as OTHdC, PCHdC, SEC, thermal field flow fractionation (ThFFF), and sedimentation field flow fractionation (SdFFF). The molecular weight separation range... 

TABLE 22.1 Column Comparison among Four Molecular Weight Separation Techniques"... 

This chapter reviews the adsorptive separations of various classes of non-aromatic hydrocarbons. It covers three different normal paraffin molecular weight separations from feedstocks that range from naphtha to kerosene, the separation of mono-methyl paraffins from kerosene and the separation of mono-olefins both from a mixed C4 stream and from a kerosene stream. In addition, we also review the separation of olefins from a C10-16 stream and review simple carbohydrate separations and various acid separations. 

Size Exclusion Chromatography Molecular Weight Separation and Column Dispersion... 

S.S. Huang, Molecular weight separation of macromolecules by hydrodynamic chromatography, in Column Handbook for Size Exclusion Chromatography, C.-s. Wu, ed.. Academic Press, San Diego, CA, 1999, p. 597. 

From Fig. 7, it is easily seen that critical conditions are the optimum conditions for separation according to the functionality. There is no molecular weight separation, and the chromatogram can be unambiguously interpreted as FTD. 

Concentration, molecular weight, separation and identification A pH meter or the color of a pH indicator is used to measure hydrogen ion concentration (see 0019). 

Thermal Field-Flow Fractionation Extension to Lower Molecular Weight Separations by Increasing the Liquid Temperature Range Using a Pressurized System, J. C. Giddings, L. K. Smith, and M. N. Myers, Anal. Chem., 47, 2389 (1975). Flow Field-Flow Fractionation A Versatile New Separation Method, J. C. Giddings, F. J. Yang, and M. N. Myers, Science, 193, 1244 (1976). 

An ideal matrix for gel filtration should consist of partides of a hydrophilic polymer, that is as inert as possible, as rigid as possible, uncharged, and of uniform size (Patel 1993). Suitable materials are naturally occurring polymers, such as agarose or dextran, which have been stabilised by chemical cross linking, and also synthetic polymers such as polyacrylamide. These materials are available as spherical partides of different diameter (10-500 pm) and pore sizes the pore size determines the range of optimal molecular weight separation (Table 4-1). 

SEC for low molecular weight separations is ideally suited for quality control, quantitation, separation of unknown and removal of polymerie species from a system. 

Polymers are mixtures of macromolecules of different molecular weight, and most commercially available products have rather broad distribution of the molecular weight. Some studies were carried out with fractions of a narrow distribution of the molecular weight, separated from commercially available polymers. Adsorption leads to fractionation as discussed above for some types of surfactants. Larger polymer molecules have higher affinity to the surface than smaller molecules composed of the same type of monomeric units. The selectivity is chiefly driven by the difference in the entropy of mixing in solution. Polydispersity of polymers is also one of the factors responsible for hysteresis loops in the adsorption-desorption cycles. 

---