Two-dimensional liquid chromatography with mixed mode stationary phases

Mixed mode stationary phases with ion-pairing reagent (acidic or basic) as integral part of hydrophobic chain offers unique selectivity, and hence, are ideal for multidimensional separations. The retention of hydrophobic components is a function of organic content, whereas that of charged species is a function of organic content, ionogenic modifier and its level in the mobile phase. Hence, by controlling the parameters influencing component retention (stationary phase and mobile phase), the selectivity of chemical components in the two-dimensional plane can be manipulated to improve the separation. A two-dimensional liquid chromatograph has been developed by coupling similar and dissimilar mixed mode stationary phases in the two dimensions. This technique has immense potential in resolving co-eluting components as the retention mechanism in the two-dimensions are complementary. However, with only part of the primary column eluent sampled into the secondary column, the technique is limited to qualitative analysis.