Handbook of Size Exclusion Chromatography and Related ...

Figure 12 Analysis of poly-2-vinyl pyridine standards: two columns PL aquagel–OH
50, 300 7.5 mm, eluant 0.25 M NaNO 3 and 0.01 M NaH 2PO 4, pH 3, flow rate 1 mL/min,
detector RI: (1) Mp ¼ 600,000; (2) Mp ¼ 200,000; (3) Mp ¼ 50,000; (4) Mp ¼ 20,000.
hydrophobicity in the sample then it may be necessary to add some organic
modifier to the mobile phase.
Even if the ionic sample solutions are prepared from the eluent, when the
mobile phase consists of a salt solution there will often be a peak near total
permeation due to the salt. This is believed to be due to ion inclusion (30)
where the porous packing acts like a semipermeable membrane and an
equilibrium is established such that the ion of the same charge as the excluded
sample is forced into the pores, giving rise to a permeated peak. This can be
problematic as it may interfere with sample components and in this case column
selection may have to be adjusted to give more resolution for very small
molecules.
5 CONCLUSION
A wide variety of commercial semirigid polymer gels exists for both organic and
aqueous SEC. Following the introduction of smaller particle size packings, high-
© 2004 by Marcel Dekker, Inc.