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

Polybutylene glycol (PBG) samples largely differing in molecular weigh t M(r) are separated by gradient reversed-phase high performance liqui d chromatgraphy on C-18 C-4 Stationary phases by use of either acetoni trile 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 sample s from the extremely hydrophobic C-18 matrix. However, the elution pot ency of methanol is markedly better compared with acetonitrile presuma bly attributable to a solubility increase of sample molecules via hydr ogen bonding between its hydroxy group and the ether oxygens of the so lutes. Marked lower retention of high M, oligomers is observed on the more polar C-4 matrix and the elution power of acetonitrile is now suf ficient for the quantitative release of all investigated polyether sam ples. A substantial increase of signals eluting at higher retention ti mes 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 thu s substantial peak overlapping by superposition of the individual chro matograms a clear assignment to individual samples can be done on the basis of the different chromatographic patterns.