Separation of Polybutylene Glycols on C₁₈ and C₄ Stationary Phases

Abstract

Polybutylene glycol (PBG) samples largely differing in molecular weight M_r are separated by gradient reversed-phase high performance liquid chromatgraphy on C₁₈ and C₄ stationary phases by use of either acetonitrile or methanol as organic 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 C₁₈ 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_r oligomers is observed on the more polar C₄ 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_r 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.