Characterization of PEG in monomethyl ethers of PEG by 2-D LC

PEGs present in samples of the corresponding monomethyl ethers are analyzed by 2-D LC with LC at critical conditions as the first and liquid adsorption chromatography as the second dimension. The fractions from the first dimension are transferred to the second one by heart-cutting using a ten-port valve. The efficiency of the separation is dramatically improved by adding water to the eluate from the first dimension before the switching valve in order to have a weaker eluent in the fraction than that of the second dimension. By this procedure, the fractions are focussed and reconcentrated. The molar mass distribution of the PEG fraction can be determined with good accuracy even at very low amounts of PEG in the PEG-monomethyl ethers (down to 0.5%).