Significance of radial dispersion to effective modulation in two-dimensional liquid chromatography

As conventional liquid chromatography (LC) increasingly proves insufficient for addressing complex analytical challenges, two-dimensional LC is gaining growing interest from industrial laboratories. When coupling complementary separation mechanisms, one major challenge that continues to receive attention is mobile phase mismatch. To address this challenge, several strategies have been described in the literature for combining solvent streams to achieve dilution, they commonly involve a T-type geometry. After the convergence of two solvent streams, under laminar flow conditions, segregated flow streams may persist and reach the column inlet without significant mixing. This study explores this phenomenon and its impact on chromatography in detail, specifically in the context of modulation for two-dimensional liquid chromatography. The presence of insufficiently mixed solvents can have serious implications for analyte retention and peak shape. To address this issue, mixing can be achieved through radial dispersion by utilizing coiled tubing, which helps maintain analyte retention along with narrow and symmetrical peak shapes. In addition to modulation in 2D-LC, feed injection has also been investigated and benefits from increased radial mixing.