In principle, resolution in size-exclusion chromatography (SEC) is defined in the same manner as in other forms of chromatography. However, because SEC is typically used to characterize distributions, rather than to separate narrow peaks the implementation is different in practice.
Resolution then hinges on three factors, i.e. (i) the difference in molecular weight between analyte polymers, (ii) the standard deviation of a monodisperse peak (often a low-molecular-weight marker, such as toluene), and (iii) the absolute slope of the linear part of the calibration curve (see figure below). If elution volume is on the horizontal axis, the standard deviation must be in volume units. Alternatively, both may be expressed in time units.
By arbitrarily assuming one order of magnitude difference in molecular weight between analytes i and j, a specific resolution (Rsp) can be defined for a SEC column. In the figure (taken from Figure 4.9B in the book), the absolute slope of the calibration curve (b) is lowest for column E and thus the specific resolution is highest for this column.
To compare different packing materials for SEC a packing resolution factor (R*sp) can be introduced by normalizing for the column length. Materials with the highest R*sp values yield the best resolution in SEC.
For more information see Section 4.2.1 and 4.2.2.
