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Gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), is an accepted technique for characterizing polymers. It does not rely on chemical differences to effect the separation but separates polymer molecules on the basis of their size relative to the pores in the packing particles. Its primary use is in measuring molecular weight and molecular weight distributions. However, closer consideration reveals that the size of the polymer molecule also depends on primary and secondary structural factors. The major limitation of conventional GPC using only a concentration detector, such as a refractometer, is that it is unable to distinguish between the effects of molecular weight and structural differences on molecular size.

During the first two decades of GPC acceptance the emphasis was on improving the fundamental aspects of chromatography, such as column technology, optimizing solvents, and improving precision of analysis. But, over the past ten years there has been an increasing demand for getting more information out of GPC, driven by the need to characterize more fully an increasingly complex array of new polymers.