Separation of polybutylene glycols widely differing in molecular weight on different stationary phase by gradient RP-HPLC and detection by evaporative light scattering

Polybutylene glycols (PBG's) substantially differing in molecular weight (MW), i.e., PBG 650, PBG 1000, PBG 2000 and PBG 3000 were subjected to separation on monolithic, i.e., Chromolith SpeedRod RP-18 and Chromolith Performance RP-18, polymeric, i.e., Polymer C-18 and silica-based, i.e., Nucleosil 5C(4) chromatographic supports. Different eluent systems each consisting of a ternary gradient built up from acetonitrile, tetrahydrofuran and water were applied and monitoring of signal responses was accomplished by evaporative light scattering detection (ELSD). Fine-tuning of the gradient profiles for the different PBG's yields optimum separation of the individual oligomers of the low MW samples PBG 650 and PBG 1000 and no marked differences seem to occur on the four stationary phases used within the study. However in contrast, pronounced deviations between them were observable when applied for separation of PBG 2000 and PBG 3000. Surprisingly in the latter case the Nucleosil 5C4 support proved to be better suited for separation of sample constituents of higher MW. Although better resolution into individual oligomers, in particular of PBG 2000 and PBG 3000, was achieved on both Chromolith SpeedRod RP-18 and Chromolith Performance RP-18 when compared to the Polymer C-18 support, the good separation efficiency of the latter support is nevertheless quite remarkable making this material an additional valuable alternative for chromatographic fingerprinting at least for PBG 650 and PBG 1000.