Analysis of the molecular size distribution of polyethylene glycols by CE-UV versus HPLC with evaporative light scattering detection

A simple capillary zone electrophoresis method has been developed for the separation of polyethylene glycols (PEGs) consisting of differing amounts of polymers with different monomer numbers up to an average molecular mass of 1500. To provide both charge and detectability, the analytes were derivatized with phthalic anhydride according to a conventional method and a newly developed microwave-assisted method. While obtaining nearly equal amounts of single and double esterificated PEGs with the conventional method, the fraction of single derivatized PEGs is considerably reduced by microwave-assisted reaction. In order to compare the capillary zone electrophoresis results, an HPLC method with evaporative light scattering detection has been established. This method was successfully applied to the analysis of underivatized PEG 400, 1000 and 1500.