Separation of polyethylene glycol oligomers using inverse temperature programming in packed capillary liquid chromatography

Inverse temperature programming in packed capillary liquid chromatography coupled to evaporative light-scattering detection has been used to resolve native polyethylene glycol (PEG) oligomers. The model compound, PEG 1000, was separated on a 300 mmx0.32 mm I.D. capillary column packed with 3 mum Hypersil ODS particles with acetonitrile-water (30:70, v/v) as mobile phase. The retention of the PEG oligomers increased with increasing temperature, different from what is commonly observed in liquid chromatography. The retention times of the oligomers were approximately doubled for each 25 degreesC increment of the column temperature in the temperature range 30-80 degreesC. The oligomers were almost unretained and co-eluted at a column temperature of 30 degreesC. At 80 degreesC a baseline separation of more than 22 peaks was obtained, but the last eluting peaks were severely broadened and all oligomers did not elute. When a negatively sloped temperature ramp from 80 to 25 degreesC at -1.5 degreesC/min was applied, the peak shapes were improved, additional peaks were detected and the analysis time was reduced by 48%. In the temperature programming mode, the intra-day precision of the retention times ranged from 0.5 to 5.8% (n=5). (C) 2001 Elsevier Science B.V. All rights reserved.