Modelling of the elution behaviour in hybrid micellar eluents with different organic modifiers Original Research Article

The elution behaviour in reversed-phase liquid chromatography (RPLC), with mobile phases containing micelles, can be described according to a distribution pattern among three phases: bulk water, micellar pseudophase and stationary phase. Several mechanistic equations based on this pattern, previously used to predict the retention in hybrid mobile phases of sodium dodecyl sulphate and propanol, were checked with several organic modifiers and a group of solutes of diverse polarity. The modifiers were the alcohols 1-propanol, 1-butanol and 1-pentanol, and other organic solvents widely used in conventional RPLC such as acetonitrile and tetrahydrofuran. New models were also proposed to take into account diverse interactions of the modifiers with the micelles and the stationary phase. In spite of the differences in hydrophobicity of the three alcohols studied, the behaviour of the probe solutes in their presence was optimally described with the same equation, with relative mean fitting errors below 2%. The inclusion of the distribution of 1-butanol and 1-pentanol between bulk water and micelles in the equations produced a further increase in the accuracy. This distribution also explained the small deviations from linearity observed in the plots of 1/k vs. micellar concentration, in the presence of pentanol. The more complex behaviour of the probe solutes in micellar eluents containing acetonitrile and tetrahydrofuran required a model with a larger number of parameters to obtain errors below 3.5%.