The uses of size-exclusion chromatography

SEC in its many forms is capable of providing a vast amount of information on polymers and polymer systems. The molecular weight averages (number, weight and viscosity) can be obtained as described in this chapter. However, the most useful and well-used parameter produced is the molecular-weight distribution curve, which can be used to fingerprint the polymer. Subtle differences in all of the above parameters can affect many of the end-use properties of the polymer such as impact, tensile and adhesive strength, brittleness, drawability, cure time, melt and flow characteristics, solution properties and hardness. 

---

The ideal packing should be relatively large in diameter, 80-100 nm, and be available with a pore size range from 500 to 10,000 A. The ores should be uniform in size distribution and shallow to reduce diffusion times. Improvements of this type will lead to the use of size exclusion chromatography for particle size determinations in the routine manner in which it is now employed for molecular weight determinations. 

Gall, B.L. and Raible, C.J. "The Use of Size Exclusion Chromatography to Study the Degradation of Water Soluble Polymers Used in Hydraulic Fracturing Fluids," Polvm. Mater. Sci. Eng. 1986, 55, 572 75, Anaheim. 

For biorelevant dissolution media containing only bile salt and PL, dynamic light scattering determinations reveal that only one particle population in the micellar size range is present (Sunesen et al., 2005 llardia-Arana et al., 2006). Upon addition of free fatty acids and monoglycerides, the structure and size of the colloid phases in these media depend on absolute concentrations and the ratios between the amphiphiles. In general, a micellar fraction is still present but co-exists with particles of a vesicular size. This was also observed by Kossena and coworkers by the use of size exclusion chromatography (Kossena et al., 2003). 

In few areas of natural product chemistry does the injunction first, catch your hare so succinctly summarise the main difficulties. Whereas a battery of well-established techniques can be used for the purification of a protein from biological materials, each sub-field, and even each laboratory, in the carbohydrate purification and sequencing area tends to adopt its own extraction procedures. Polysaccharides in vivo are often heterogeneous with respect to molecular weight, which restricts the usefulness of size-exclusion chromatography. Some polysaccharides are covalently attached to other macromolecular... 

Finally polymer degradation standards should consider the use of size exclusion chromatography to supplement viscosity testing. Such testing will provide a more realistic standard for assuring proper polymer degradation. 

Examples of the application of size-exclusion chromatography to the analysis of proteins. The separation in (a) uses a single column that in (b) uses three columns, providing a wider range of size selectivity. (Chromatograms courtesy of Alltech Associates, Inc. Deerfield, IL). 

Huve, P., Verrecchia, T., Bazile, D., Vauthier, C., and Couvreur, C., Simultaneous use of size exclusion chromatography and photon correlation spectroscopy for the characterization of poly(lactic acid) nanoparticles, /. Chromatogr. A, 675, 129, 1994. 

The techniques of size-exclusion chromatography has been used effectively in checking the purity of the following pharmaceutical substances for their respective impurities, such as ... 

The role of size exclusion chromatography is the separation of rather complex coal liquids into simpler fractions. The retention volume can be used to help Identify the chemical structure where GC-MS is unable to identify its possible structure. For example biphenyl and dihydroacenaphthene have the same molecular formula as well as similar mass spectral fragmentation patterns. Coal liquids contain both species. The one which appears first (lower SEC retention volume) is biphenyl (GC ret. time = 17 min. in Figure 5-6). Dihydroacenaphthene appears later at longer SEC retention volume and is identified in Figure 5-12 at GC retention time of 13 minutes. The former has a longer structure compared to the latter. 

Earlier literature had demonstrated that gelatin samples could be arbitrarily subdivided into a number of molecular weight classes (Table 8.4), and these could be identified by the careful use of size-exclusion chromatography (Figure 8.10). By adding two more categories, a logical explanation for the structures found based on... 

The advent of size exclusion chromatography in the 1960 s provided an alternative to drying polymer-polymer-solvent samples to determine the equilibrium phase compositions. Size exclusion chromatography separates solvents from polymers and to a varying extent, polymers from polymers, based on the size of the molecules in solution. Ultraviolet spectrometry and refractive index detectors may be used to determine the concentrations of each of the polymers in each of the phases (Lloyd et al., 1980). 

Fig. 2.11. The principle of size exclusion chromatography Large molecules do not enter the pores and pass the matrix unretained, very small molecules spend a long time in the pores, but there is no differentiation between molecular sizes. Only within a critical size range is there a relation between residence time and molecular size, which can be used for separation.

The high salt concentrations used can present a challenge for the HPLC equipment. Pumps with seal-wash are prrferred. If chloride buffers are used, HPLC systems with nonmetallic fluid paths are recommended. It is also advisable to flush the salt solution out of the system when it is not in use. Temperature and pH can affect the separation and should therdbre be controlled. But both the temperature effect and pH effect are smaller than in other forms of chromatography (with the exception of size-exclusion chromatography). 

These spectra allowed the characterisation of the additives by spectral library search and/or spectral interpretation. The usefulness of the spray-jet interface system for the coupling of size exclusion chromatography(SEC) and FTIR spectrometry was examined on the basis of the analysis of a PS standard mixture. Representative IR spectra of the SEC effluent indicated that the SEC-FTIR system could be used for the determination of compositional changes across the polymer MWD. 25 refs. 

Early researchers in the application of size exclusion chromatography (SEC) to asphalt (1-7) noted that SEC (also called GPC, gel permeation chromatography) was very sensitive to differences in asphalts and to changes in composition. This was exploited by Adams and Holmgreen (8) to show differences between various asphalts and between asphalts from the same supplier at different locations. Glover et al. (9,10) used SEC to show how asphalts from a number of suppliers changed with the seasons. It has been used to compare fractions produced by preparative SEC and other methods (9,11-16). 

The convenience of size exclusion chromatography (SEC) as a means for the determination of the molecular mass distribution of a wide variety of synthetic polymers was appreciated early [1]. It was developed, however, for low-temperature application principally for reasons of safety and ease of use. Tetrahydrofuran, THF, had been adopted as a general-purpose mobile phase, and its low boiling point and the ease with which it formed peroxides restricted its use to temperatures below 40°C. This meant that many commercially important polymers, such as polyethylene, polypropylene, and polyaryl ether ketone could not be analysed, since they required high temperatures for dissolution. The high-boiling halogenated aromatics and substituted phenols were found to be suitable solvents for these polymers, and with increased temperature the scope for SEC was vastly increased. 

---