SEPARATION OF POLYBUTYLENE GLYCOLS ON C-18 AND C-4 STATIONARY PHASES

Polybutylene glycol (PBG) samples largely differing in molecular weight M(r) are separated by gradient reversed-phase high performance liquid chromatgraphy on C-18 C-4 Stationary phases by use of either acetonitrile or methanol as organic and C modifiers and signal monitoring by means of evaporative light scattering detection. Neither acetonitrile nor methanol are sufficient for the quantitative elution of all samples from the extremely hydrophobic C-18 matrix. However, the elution potency of methanol is markedly better compared with acetonitrile presumably attributable to a solubility increase of sample molecules via hydrogen bonding between its hydroxy group and the ether oxygens of the solutes. Marked lower retention of high M, oligomers is observed on the more polar C-4 matrix and the elution power of acetonitrile is now sufficient for the quantitative release of all investigated polyether samples. A substantial increase of signals eluting at higher retention times and thus representing oligomers with higher M, becomes evident in the range PBG 650 < PBG 1000 < PBG 2000 < PBG 3000. Although the PBGs exhibit a broad ''within-sample'' oligomeric M(r) distribution and thus substantial peak overlapping by superposition of the individual chromatograms a clear assignment to individual samples can be done on the basis of the different chromatographic patterns.