Single-pump heart-cutting two-dimensional liquid chromatography applied to the determination of fatty alcohol ethoxylates

Abstract

A setup for heart-cutting bi-dimensional liquid chromatography (LC–LC), constructed with a chromatograph provided with a single pump, an auxiliary 6-port 2-position valve (V6/2) and a column selector valve (VCS), is described. The possible ways of connecting the two valves for LC–LC, namely with V6/2 first followed by VCS and vice versa, are compared. The possibility of using the setups for preconcentration followed by the backwards transfer of the preconcentrated solutes to the detector or to a second column is also shown. The V6/2-first configuration for LC–LC was applied to the characterization of industrial fatty alcohol ethoxylates (FAEs) using UV–vis detection. For this purpose, the phthalates of the FAE oligomers were first obtained. The hydrocarbon series were separated along the 1st dimension by MeOH/water gradient elution on a C8 column at 60°C. Selected segments of the eluate were transferred to the 2nd dimension, where the EO oligomers of the isolated series were resolved by gradient elution with a complementary ACN/water mobile phase on a C8 column at 25°C. In addition, an average response factor of the hydrocarbon series of FAEs was proposed. To apply the factors, the average EO number of the series is first established by chromatographing one of the series along the 2nd dimension. Then, the factors are used to correct the peak areas of the isolated series which are obtained along the 1st dimension chromatogram, thus allowing the fast and accurate determination of the series in industrial FAEs. The method is particularly useful to characterize FAEs having large average EO numbers or constituted by mixtures of even and odd series.