Poly(allylamine) is a cationic polymer. When using GPC analysis of cationic polymers the selection of the eluent which prevents ionic and hydrophobic interactions between the sample and gel makes a measurement successful. In order to control the ionic interaction between a sample and gel, salt should be added to the eluent. But if the salt contains a multivalent anion such as phosphate or sulfate, a sample may not dissolve or precipitate after the dissolution. However, if the salt contains one valent anion such as nitrate and chloride, precipitation of a sample should not take place. Here, the salt concentration in the eluent was investigated under the various concentration of sodium nitrate in the eluent. In order to reduce hydrophobic interactions between a sample and gel, 0.5M acetic acid was added to the eluent. A comparison of chromatograms of poly(allylamine) was measured under the various concentration of sodium nitrate in the eluent is shown in Fig.1. In the case of the addition of 0.02M sodium nitrate in the eluent, high molecular weight poly(allylamine) was adsorbed to the gel material and was not eluted from the column. When the salt concentration of sodium nitrate is more than 0.1M, the adsorption of a sample is suppressed and a right chromatogram is obtained. The relation between the molecular weight of poly(allylamine) and elution volume with GPC-MALS is shown in Fig.2. When the concentration of sodium nitrate in the eluent fell between 0.1M – 0.2M, poly(allylamine) was eluted in the molecular weight order. The relation between the RMS radius (size of the molecule in the solution) of poly(allylamine) and elution volume with GPC-MALS is shown in Fig.3. When the concentration of sodium nitrate is low, molecule of the polymer spreads out and RMS radius becomes large, as the result, poly(allylamine) is eluted early. When the salt concentration is 0.1-0.2M, we can see the influence of the diffusion of molecule is decreasing according to the salt concentration, and separation is performed in the molecular size order. From the above result, in the measurement of poly(allylamine) with SB-806M HQ, the eluent of 0.5M acetic acid + 0.1M – 0.2M sodium nitrate is sutable for this analysis.
Sample : 0.2% Poly(allylamine), 100micro-L
Columns : Shodex OHpak SB-806M HQ (8.0mmID*300mm) x 2 Eluent : 0.5M CH3COOH + nM NaNO3 Flow rate : 1.0mL/min Detector : Shodex RI, MALS (Multi-Angle Laser Light Scattering Detector) Column temp. : 40°C