INVESTIGATION OF CHROMATOGRAPHIC BEHAVIOR OF ETHOXYLATED ALCOHOL SURFACTANTS IN NORMAL-PHASE AND REVERSED-PHASE SYSTEMS USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY

Retention behaviour of ethoxylated alcohols was investigated on octade cyl silica, unmodified silica and aminosilica columns. Good separation according to the alcoholic alkyl length is achieved in reversed-phase systems. The elution order of the oligomers with different numbers of oxyethylene groups depends on the type of the organic solvent (methan ol or acetonitrile) and on its concentration in the mobile phase. Diff erent retention behaviour of lower and higher oligomers was observed. The distribution of the oligomers according to the number of oxyethyle ne units is suppressed, but it overlaps with the peak distribution acc ording to the alkyl length in mobile phases containing high concentrat ions of acetonitrile. In normal-phase systems, the alkyl length affect s the retention much less than the number of oxyethylene units. Better separation than on unmodified silica gel columns can be achieved on a chemically bonded aminosilica column in 2-propanol-n-hexane and espec ially in acetonitrile-water-dichloromethane mobile phases. Possible re tention mechanisms in the systems studied are discussed. The retention is strongly affected by solvation of the oxyethylene groups by the mo bile phase. The retention factors of higher oligomers with bimodal mas s distribution can be described using a simple equation. HPLC-MS with atmospheric pressure chemical ionization allows sensitive detection, e asy identification and reconstruction of the chromatographic peaks in chromatograms of complex mixtures of oligomers with different numbers of methylene and oxyethylene groups. (C) 1998 Elsevier Science B.V. Al l rights reserved.