Handbook of Size Exclusion Chromatography and Related ...

Table 4 Typical Eluent Systems for Synthetic Water Soluble Polymers
Type of polymer Typical sample Suitable eluent
Nonionic, hydrophilic Polyethylene oxide,
polyethylene glycol
Pure water
Nonionic, hydrophobic Polyvinylpyrrolidone 0.1–0.2 M salt/buffer with 20–50%
organic solvent
Anionic, hydrophilic Sodium polyacrylate,
sodium hyaluronate,
carboxymethyl cellulose
0.1–0.3 M salt/buffer, pH 7–9
Anionic, hydrophobic Sodium polystyrene 0.1–0.3 M salt/buffer, pH 7–9 with
sulfonate
20–50% organic solvent
Cationic, hydrophilic Chitosan, poly-2-vinyl
pyridine
0.3–0.8 M salt/buffer, pH 2–7
Cationic, hydrophobic Polyethyleneimine 0.3–0.8 M salt/buffer, pH 2–7 with
20–50% organic solvent
For nonionic polymers, pure water can often be used as eluent although a
lowionicstrengthisagoodsafetymeasureandaddsadegreeofreproducibilityto
the system. Polyethylene oxide and polyethylene glycol are characteristic of this
sample category.
For ionic samples it is recommended that salt/buffer systems are used as
eluents. The salts most commonly used are sodium sulfate, sodium nitrate, and
sodium acetate, because these cause little corrosion to stainless steel column
hardware even at low pH. Ionic strength is varied according to sample type but
generally does not exceed 1.0 Mas increasing salt concentration will promote
hydrophobic interaction. Often abuffer is used to allow pH to be controlled.
Anionic polymers may be eluted using 0.1–0.3 Msalt/buffer at pH 7–9.
Figure 10 shows the analysis of polyacrylic acid (sodium salt), which is atypical
example.Polystyrene sulfonate (sodiumsalt) isalsoananionicpolymer,butoften
does not elute under such conditions as it is relatively hydrophobic. Although the
salt/buffer systemis sufficient to suppressthe ionic interaction, adsorption due to
hydrophobic interaction occurs and this has to be overcome by introducing some
organic modifier to the mobile phase as shown in Fig. 11. In the case of PL
aquagel–OH, methanol is recommended as an organic modifier although with
other packings different solvents may be used (e.g., acetonitrile with TSK PW
columns). The manufacturers’ recommendations on the use of organic solvents
withaqueouspackingsshouldalwaysbefollowedcarefullyasthewrongchoiceof
solvent may irreversibly damage the column.
Cationic polymers may be eluted using rather higher salt concentrations,
0.3–1.0 M, and pH in the range 2–7. Atypical analysis of poly-2-vinyl pyridine
is shown in Fig. 12. As with the anionic samples, if there is ahigh degree of
© 2004 by Marcel Dekker, Inc.