High-performance liquid chromatography and detection of polyethers and their mono(carboxy)alkyl and -arylalkyl substituted derivatives

This review deals with high-performance liquid chromatographic (HPLC) separation techniques and detection methods for a wide variety of polyether derivatives, including alkyl-, arylalkyl-, carboxyalkyl-substituted polyethylene glycols mainly applied as non-ionic surfactants (NIS), and native (underivatized) polyethylene glycols (PEGs), polypropylene glycols (PPGs) and polybutylene glycols (PBGs) widely used in either industrial or pharmaceutical applications. Normal-phase (NP) and reversed-phase (RP) systems have been considered for NIS, the NP technique being the most suitable for separation according to the number of ethoxylate units, whereas separation according to the hydrophobic alkyl chain is favored on RP stationary phases. At variance with NIS mainly RP-HPLC is applied for native (underivatized) polyethers of the PEG, PPG and PEG type. Ion-exchange chromatography (IEC) is still a minor technique for the separation of PEG derivatives, which exploits the capability of the 1,2-dioxoethylene moiety to form complexes with potassium ions. Liquid chromatography under critical conditions (LCCC) is the method of choice for separation of polyethers according to their chemical composition and is preferably applicable to copolymers built up from different components. A multitude of detection principles substantially differing in either selectivity or sensitivity has been successfully used for signal monitoring, with detection by measurement of refractive indexes (RI), UV absorption, fluorescence acid responses from evaporative light scattering of ''solid'' droplets being the most prominent. Nevertheless, UV detection still dominates because of the existence of the phenyl chromophor in many NIS and the ease of derivatization of polyethers lacking an inherent aromatic moiety with a large variety of chromophoric agents. Additionally, well-established methods are available for low wavelength UV detection below 200 nm even for the native polyethers.