Handbook of Size Exclusion Chromatography and Related ...

When an anionic or cationic acrylamide polymer is analyzed, the ionic group
of the stationary phase should be considered before selecting a column. Sasaki and
colleagues (43) reported that the TSK Gel PWXL columns have small amounts of
weakly anionic groups. Lin and Getman (44) observed the adsorption of a high
MW acrylamide/DMDAAC cationic polymer in the TSK Gel PWXL columns.
Therefore, the TSK Gel PW columns are recommended for analyzing cationic and
amphotoric acrylamide polymers.
Simple salts such as sodium chloride or sodium sulfate are added to the
mobile phase to minimize the polyelectrolyte effect of the charged acrylamide
polymers. The optimal ionic strength of the mobile phase can be determined
by measuring the intrinsic viscosity [h] of the polymer solutions with
increasing concentration of simple salt until the intrinsic viscosity becomes
constant. If a linear calibration curve is desired, the different pore sizes of
columns should be investigated for a particular range of MW. If a very slow
flow rate such as 0.1–0.3 mL/min is required for a very-high-molecular-weight
sample in a narrow MW range, a single column may be used to reduce the
analysis time. Research should be conducted to provide adequate information
for selecting columns and mobile phase. The columns and mobile phases that
have been used to analyse polyacrylamide and its copolymers and terpolymers
are summarized in a list of SEC conditions, which are compiled in the
Appendix at the end of this chapter.
2.2 Sample Preparation
Sample preparation is a very important step for SEC analysis. The MW of a
polymer can be changed unintentionally during sample preparation. Use the
mobile phase to prepare samples. If the low MW tail of the chromatogram overlaps
with the salt peak, replace the mobile phase with an appropriate amount of water to
obtain a negative polarity salt peak. The quantity of water to be used depends on
the concentration to be prepared and the percentage of active polymer in the
sample. It can be determined from a series of SEC experiments with varying
amounts of water added to the sample until a negative polarity salt peak is
obtained. The optimum concentration of SEC sample depends on the MW of the
polymer. Lundy and Hester (50) suggested that the polymer solution injected into
the columns should not be greater than one-half the reciprocal of its intrinsic
viscosity. If an unusual pressure trace caused by a high viscosity of a solution is
observed during the injection, reduce the concentration and remove the precolumn
filter, if such a filter is present.
Filter size selection depends on the MW and solution concentration. Use an
appropriate size of filter to prepare polymer solutions, so the large molecules will
not be excluded by the filter. If there is no information about the MW of the
© 2004 by Marcel Dekker, Inc.