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

摘要

Separation of the polyethylene glycols PEG-200, PEG-300, PEG-600 and PEG-1000 by gradient high performance liquid chromatography is reported on a C18as 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 Mnand Mwvalues 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 Rson the C18matrix, the inverse effect was observed with PEG-600 and PEG-1000, which reveal much better Rson bare silica gel. Further, a dependence of the Rsof 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 acetone acetonitrile. A hypothetical view of the improved separation of PEG-600 and PEG-1000 oligomers is given on the basis of prevailing hydrophilic interactions between polar sites of polyethers and silanol groups of the stationary phase. Additionally a mechanistic hypothesis, which considers the superiority of acetonitrile and acetone versus methanol with respect to the Rsof 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).