Microfluidic tools for multidimensional liquid chromatography

The research in this thesis focuses on the development of a microfluidic component, namely a micromixer, which could be implemented for the improvement of two-dimensional liquid chromatography (2D-LC), used for the analysis of complex samples. The common problem of mobile phase incompatibility between dimensions in 2D-LC requires the utilization of a mixing device in the interface to adjust mobile phase compositions. A mixer should therefore provide fast mixing in-line at different flow rate ratios for a wide range of flow rates, have a small volume, and be able to withstand brief pressure pulses up to a few hundred bar, due to its connection to switching valves used to shuttle sample between columns. The author describes the design and realization of a micromixer based on chaotic advection, a mechanism for mixing which involves perturbation of laminar flow within a microchannel, using obstacles (grooves) in the shape of herringbone that cause a recirculating or vortical flow pattern perpendicular to the direction of flow. This significantly increases the contact area between two solution streams, which speeds up the mixing process. The micromixer was realized in different materials to For the prove of mixing concept it was fabricated in poly(dimethylsiloxane) (PDMS) using soft-lithography. In order to satisfy the stringent pressure requirement, a microfluidic mixer was fabricated inside a block of fused silica using Selective Laser-Induced Etching (SLE) and in cyclic olefin copolymer (COC) using micromilling. Finally, a microfluidic mixer was successfully implemented in a 2D HILIC×RP-LC system for analysis of nylon samples.