CHROMATOGRAPHIC INVESTIGATIONS OF OLIGOMERIC ALPHA,OMEGA-DIHYDROXY POLYETHERS BY REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND EVAPORATIVE LIGHT-SCATTERING AND UV DETECTION

The separation of the three hydroxy-terminated polyethers, PolYethylen e glycol 1000, Polypropylene glycol 1200 and polybutylene glycol 1000, on reversed-phase separation media differing markedly in the length o f the alkylsilyl chain is described. Underivatized polyethers were mea sured by evaporative light scattering detection, whereas the correspon ding 3,5-dinitrobenzoyl derivatives were monitored by UV detection at 254 nm. The detection limits were ca. 5, 10 and 20 mug for native poly ethylene glycol 1000, polypropylene glycol 1200 and polybutylene glyco l 1000, respectively, and 0.5, 1 and 2 mug for the corresponding 3,5-d initrobenzoyl esters. A clear dependence of t(R) and R(s) values on th e polarity of the analyte was observed in the sequence polyethylene gl ycol 1000 < polypropylene glycol 1200 < polybutylene glycol 1000 for e ach adsorbent used. Marked attenuation of analyte retention occurred w ith increasing polarity of the stationary phase in the sequence C18 > C-8 > C4 > C(Phenyl) almost-equal-to C1 and concomitant loss of peak r esolution of high-molecular-mass oligomers became increasingly evident . The solvent strength of acetonitrile was not sufficient for complete elution of polybutylene glycol and polypropylene glycol oligomers wit h higher molecular mass from the strongly hydrophobic C18 stationary p hase, which however was markedly improved with methanol as organic mod ifier. Different possible alternatives are discussed in order to give a reasonable explanation of the separation mechanism.