High-speed characterization and quantification of polypropylene glycol based oligomeric mixtures by hydrophilic interaction liquid chromatography at critical conditions and mass spectrometry (LCCC/Q‑TOF MS)

A rapid method for determination and characterization of polypropylene glycol diglycidylether and related oligomers (dGE-PPG) has been developed. The method is based on liquid chromatography at critical conditions coupled to high-resolution mass spectrometry (LCCC/MS). The LCCC method is operated in hydrophilic interaction liquid chromatography (HILIC) mode with acetonitrile/water at isocratic conditions using a core-shell silica column. The developed method was found to be superior to conventional size exclusion chromatographic as well as reversed phase (RP) chromatographic techniques when coupled to mass spectrometry. Mass spectral overlap between different polypropylene glycol based compound classes that leads to over- and underestimation of such could be avoided by using the new method. In contrast to most published LCCC separations, this method is based on HILIC instead of RP or normal phase (NP) liquid chromatography. It provided higher chromatographic resolution between PPG based compound classes bearing different polar end groups. A run time of less than 2 minutes is achieved with high MS sensitivity at high organic modifier content, which facilitated compound identification and quantitation. Multiple compound classes could be identified, each having a distribution of propylene glycol oligomers. The methodology was straightforward to implement, and critical conditions could be maintained over the course of several months.