Separation of Polyethylene Glycol Oligomers on Normal-Phase and Reversed-Phase Materials by Gradient High Performance Liquid Chromatography and Detection by Evaporative Light Scattering. A Comparative Study

Abstract

Separation of the polyethylene glycols PEG-200, PEG-300, PEG-600 and PEG-1000 by gradient high performance liquid chromatography is reported on a C₁₈ as well as a Si 80 column in aqueous mixtures of acetonitrile, acetone and methanol as organic solvents. Detection was performed by means of evaporative light scattering. Further, the M_n and M_w values were determined by gel permeation chromatography and refractive index detection. Marked differences in the chromatographic behaviour occured between the two stationary phases with all three modifiers. Whereas PEG-200 and PEG-300 exhibited better peak resolution R_s on the C₁₈ matrix, the inverse effect was observed with PEG-600 and PEG-1000, which reveal much better R_s on bare silica gel. Further, a dependence of the R_s of the PEG-600 and PEG-1000 samples (consisting of a substantially higher number of oligomers versus PEG-200 and PEG-300) from the organic modifier was seen, which increases in the range methanol s of oligomers is discussed by the assumption of different hydrogen bonding mediated solventstationary phase interactions implying a preponderance of adsorption (acetonitrile, acetone) versus partition chromatography (methanol).