ABSTRACT
Size exclusion chromatography (SEC), the technique that is the subject of this monograph, is the generic name given to the liquid chromatographic separation of macromolecules by molecular size. It has been taken to be generally synonymous with such other names as gel permeation chromatography (GPC), gel filtration chromatography (GFC), gel chromatography, steric exclusion chromatography, and exclusion chromatography. The “gel” term generally connotes the use of a nonrigid or semirigid organic gel stationary phase whereas SEC can pertain to either an organic gel or a rigid inorganic support. Despite this, the term GPC is commonly used interchangeably with SEC. In this chapter we shall focus on high-performance (or highpressure) SEC, which requires the use of rigid or semirigid supports to effect rapid separations, lasting typically 20 minutes to one hour. (More recently, a series of highthroughput SEC columns have been introduced by several vendors. While these columns are not capable of the same degree of quantitative discrimination as the analytical SEC column, they offer a nominal five minute analysis time for comparative purposes.)
The primary purpose and use of the SEC technique is to provide molecular weight distribution (MWD) information about a particular polymeric material. zv2 The graphical data display typically depicts a linear detector response on the ordinate vs. either chromatographic elution volume or, if processed, the logarithm of molecular weight on the abscissa. One may ask, if SEC relates explicitly to molecular size, how can it directly provide molecular weight information? This arises from the relationship between linear dimension and molecular weight in a freely jointed polymeric chain (random coil): either the root mean square end-to-end distance or the radius of gyration is proportional to the square root of the molecular weight (1). It follows that the log of either distance is proportional to (one-half) the log of the molecular weight.
