Thin-layer and gel permeation chromatographic separation of low molecular weight polyethylene glycol oligomers

We describe a gel permeation and a thin-layer chromatographic technique for the complete resolution of oligomers of ethylene glycol up to a chain length of fourteen ethylene oxide [OCH2CH2] units. We employed columns of Bio-Gel P-2 with 0.02 mol/l ammonium acetate as the eluant to prepare milligram quantities of each of the individual oligomers. Thin-layer chromatography on silica gel G plates with an ethyl acetate/methanol/water solvent provides a sensitive and simple method for monitoring multiple specimens. We determined the flame ionization detector response of purified individual ethylene glycol oligomers relative to tetraethylene glycol. These data permit the accurate quantification of the oligomeric profile of commercially available mixtures of low molecular weight polyethylene glycols (PEG). When PEG 400 is administered orally to normal subjects, aged three months through adulthood, they excrete in their urine a mixture of unmetabolized oligomers with a mean molecular weight of 360 +/- 14 daltons. The ability to measure absolute, rather than relative, amounts of ethylene glycol oligomers will permit more accurate studies of passive intestinal permeability in human subjects.