Seamless Combination of High-Pressure Chip-HPLC and Droplet Microfluidics on an Integrated Microfluidic Glass Chip

We introduce an approach for the integration of high performance liquid chromatography and droplet microfluidics on a single high-pressure resistant microfluidic glass chip. By coupling these two functionalities, separated analyte bands eluting from the HPLC column are fractionated into numerous droplets in a continuous flowing oil phase. The compartmentalization of the HPLC-eluate in a segmented flow was performed with droplet sizes of approximately 1 nL and with droplet frequencies reaching up to 45 Hz. This approach prevents peak dispersion and facilitates post column processing of chromatographic fractions on chip. A reliable generation of droplets is also possible in reversed phase gradient elution mode as demonstrated by applying a solvent gradient from 20% to 100% acetonitrile. A chip design with an incorporated dosing unit enabled the directed postcolumn addition of reagents to individual droplet fractions. The capability of this dosing function was successfully evidenced by post column addition of a reagent which quenches the fluorescence signal of the analytes. The chip-integration of gradient HPLC, fractionation, detection and post column addition of reagents opens up new avenues to perform multistep chemical processes on a single lab-on-a-chip device.