REVERSED-PHASE LIQUID-CHROMATOGRAPHIC SEPARATION OF LINEAR ALKYLBENZENESULFONATES - EFFECT OF MOBILE-PHASE IONIC-STRENGTH

Linear alkylbenzenesulfonate (LAS) homologues and positional isomers are separated on C,, and polystyrene-divinylbenzene reversed stationary phases using an acetonitrile-water + sodium chloride mobile phase. Retention of the LAS surfactants and separation selectivity, efficiency, and resolution are enhanced according to the mobile phase ionic strength and the ionic strength electrolyte cation. The enhanced column performance is due to Stern-Gouy-Chapman double layer interactions at the reversed stationary phase surface. The optimum mobile phase cations of those studied are Na+, Mg2+ and Ba2+. Isocratic or gradient elution can be used with detection by either UV absorbance (2.5 pmol detection limit at signal-to-noise ratio of 3) or by conductance following postcolumn anionic micromembrane suppression (130 pmol detection Limit at signal-to-noise ratio of 3). Resolution of the LAS positional isomers is most favorable by using a gradient where acetonitrile increases and sodium chloride decreases simultaneously in an acetonitrile-water + sodium chloride mobile phase.