A digital microfluidic interface between solid-phase microextraction and liquid chromatography–mass spectrometry

• Solid-phase microextraction (SPME) and HPLC coupled with digital microfluidics.
• Analytes extracted into a SPME were collected into a desorption droplet with automated digital microfluidic actuation.
• Preconcentration of analytes was achieved because of the low volume of desorption solvent.
• The method was applied to the quantitation of steroid hormones in human urine.

We introduce a method to couple solid-phase microextraction (SPME) with HPLC-MS using digital microfluidics (DMF). In the new system, SPME fibers are used to extract analytes from complex sample solutions, after which the analytes are desorbed into solvent droplets in a DMF device. The open geometry of DMF allows straightforward insertion of SPME fibers without requiring a complicated interface, and automated droplet manipulation enables multiplexed processing of the fibers. In contrast to other multiplexed SPME elution interfaces, the low volumes inherent to DMF allow for pre-concentration of analytes prior to analysis. The new SPME-DMF-HPLC-MS method was applied to the quantification of pg/mL-level free steroid hormones in urine. We propose that this new method will be useful for a wide range of applications requiring cleanup and pre-concentration with convenient coupling to high-performance analytical techniques.