The comparison of chromatograms of mixture of PEG(MW: 20000, 4000, 1000, 400) and Ethyrene glycol (EG) with Asahipak GF-310 HQ column depending on the composition ratio of water and methanol is shown fig.1. When 100% of water is used for eluent, as compared with the case where methanol/water is used for eluent, PEG (MW: 4000, 1000, 400) elute behind time. This phenomenon is related to hydrophobicity of gel of GF-310 HQ column. The hydrophobic interaction may araise between the hydrophobic portion of PEG and the hydrophobic portion of gel, as the result, reverse phase mode may work and a higher hydrophobic sample is eluted later. Since molecule size of PEG MW: 20000 is so large that it cannot go into the pore of gel, PEG MW: 20000 is excluded from the pore of gel. Therefore, the area of PEG in contact with gel is small, and hydrophobic interaction does not work. So, PEG MW: 2000 is not retained. If methanol is added to eluent, the polarity of eluent will turn into the polarity of gel closely. In this case, hydrophbic interaction of PEG and gel is lost and PEG is separated with SEC mode. Furthermore, when the eluent is 100% methanol, the polarity of gel and eluent is reversed and normal phase mode works. An interaction between the polar portion of a sample, and the polar portion of gel works and it becomes later to elute a sample as polarity of a sample becomes high.
Please refer to Influence of Analysis of PEG Mixtures with GS-320 HQ by Composition of Eluent.
Sample : 0.1% each, 100micro-L
1. Poly(ethylene glycol) (MW: 20,000)
2. Poly(ethylene glycol) (MW: 4,000)
3. Poly(ethylene glycol) (MW: 1,000)
4. Poly(ethylene glycol) (MW: 400)
5. EG, Ethylene glycol
Column : Shodex Asahipak GF-310 HQ (7.5mmID*300mm)
Detector : Shodex RI
Column temp. : 30deg-C