Handbook of Size Exclusion Chromatography and Related ...

necessarily comparable. For this reason comparisons of packing materials are best
made based on the exclusion limit and pore volume calculated from the SEC
calibration curves supplied by the manufacturer. A typical range of calibration
curves are shown in Fig. 2 for PLgel individual pore size gels.
Individual pore size packings for SEC have a finite separation capacity,
which is concentrated in a limited molecular weight range. Although the resolution
of such columns is high, the relatively narrow range of molecular weight limits
their use to SEC analyses of narrow molecular weight distribution polymers or
samples. In practise, SEC columns of different pore size are connected in series to
provide a wider molecular weight separation range (14). Most SEC users prefer
convenient systems that provide a wide molecular weight separation range to
analyse polymers of different molecular weight and distribution without having to
change and recalibrate columns. In combining individual pore size columns for
this purpose it is important to consider the pore size distributions of each column
type. The dimensions of all the columns will remain constant but pore volume may
vary from one gel to another. This has the effect of giving variable degrees of
resolution over specific regions of molecular weight. Columns with widely
overlapping molecular weight resolving ranges were often used in series, for
example, 10 6 ,10 5 ,10 4 ,10 3 , 500 A ˚ . However with the development of smaller
particles yielding higher column efficiencies, this number of columns, and
therefore analysis times, has become excessive (15).
Figure 2 SEC calibration curves for PLgel individual pore size gels, column dimensions
300 7.5 mm, eluant tetrahydrofuran, flow rate 1 mL/min, calibrants narrow
polydispersity polystyrene, detector ultraviolet (UV) 254 nm.
© 2004 by Marcel Dekker, Inc.