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

Inverse temperature programming in packed capillary liquid chromatography c oupled to evaporative light-scattering detection has been used to resolve n ative polyethylene glycol (PEG) oligomers. The model compound, PEG 1000, wa s separated on a 300 mmx0.32 mm I.D. capillary column packed with 3 mum Hyp ersil ODS particles with acetonitrile-water (30:70, v/v) as mobile phase. T he retention of the PEG oligomers increased with increasing temperature, di fferent from what is commonly observed in liquid chromatography. The retent ion 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 temperatur e of 30 degreesC. At 80 degreesC a baseline separation of more than 22 peak s 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 impro ved, additional peaks were detected and the analysis time was reduced by 48 %. In the temperature programming mode, the intra-day precision of the rete ntion times ranged from 0.5 to 5.8% (n=5). (C) 2001 Elsevier Science B.V. A ll rights reserved.