Improved separation of polyethylene glycols widely differing in molecular weight range by reversed-phase high performance liquid chromatography and evaporative light scattering detection

Polyethylene glycols (PEGs) of nominal molecular weight (M) 200, 400, 600, 1000, 1500, 3000, 4000 and 6000 were chosen as model compounds and subjecte d to reversed-phase high performance liquid chromatography (RP-HPLC) on an octadecasilyl silica gel (C-18) stationary phase using a binary gradient co mposed of acetonitrile and water and evaporative light scattering detection (ELSD). Satisfactory resolution of oligomers up to M of 3000 was accomplis hed; the higher M samples PEG-4000 and PEG-6000 could not be further resolv ed into the constituent oligomers and therefore, M = 4000 marks the upper l imit of oligomer resolution. Despite some peak overlapping as a consequence of the more or less broad oligomer distribution, individual types of PEG s amples can be distinguished from each other by their characteristic chromat ographic fingerprint patterns, as shown with a mixture consisting of PEG-40 0, PEG-1000, PEG-3000, PEG-4000 and PEG-6000. For this reason, the method i s well-suited for characterization of samples containing PEGs widely differ ing in M. In addition, matrix assisted laser desorption ionization time of flight mass spectroscopy (MALDI-TOF/MS) performed with PEG-600, PEG-1000 an d PEG-3000 revealed that the optimum degree of oligomer resolution has been achieved by use of the present method.