SEPARATION OF ACETYLATED POLYPROPYLENE GLYCOL DIAMINES AND TRIAMINES BY GRADIENT REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND EVAPORATIVE LIGHT-SCATTERING DETECTION

Polypropylene glycol di- and triamines, the so-called Jeffamines, were reacted with a mixture of equal volumes of acetic anhydride and pyrid ine to give the corresponding acetamides prior to chromatographic sepa ration by reversed-phase high-performance liquid chromatography using a linear binary solvent gradient and evaporative light scattering dete ction (ELSD). The procedure was applied to decrease silanophilic inter actions of the solutes with the column matrix in order either to impro ve the peak resolution R(s) or to decrease peak tailing. Removal of ex cess of derivatizing agent prior to sample injection is not required o wing to the volatility of pyridine, which does not yield any ELSD resp onse. Therefore, the signals of oligomers with lower retention that ar e hidden by the broad and strongly tailing pyridine peak when measured by UV detection, are now clearly detectable. Separation was performed on C-18, C-8, C-6, C-4 and C-1 stationary phases with either acetonit rile or methanol as organic modifiers. With acetonitrile either comple te elution or excellent separation of the low-molecular-mass samples ( M(r) approximate to 400) is achieved on the C-18, C-8, C-6 and C-4 mat rices. However, R(s) decreases with increasing M(r) but the recoveries of high-M(r) samples (M(r) approximate to 2000-5000) increase markedl y with decreasing hydrophobicity of the stationary phase in the order C-18 < C-8 < C-6 < C-4. Complete elution of the whole family of invest igated polyether amines was accomplished with either acetonitrile on a C-1 column or methanol on all sorbents used in the study. The optimum peak resolution was obtained on a C-4 column with either acetonitrile or methanol. Complete elution of all samples in particular on matrice s with either high or intermediate hydrophobicity with methanol compar ed with acetonitrile is presumably attributable to a better solvation of the polypropylene glycol backbone by hydrogen bonding between the e ther oxygens and the hydroxyl group of the protic solvent.