Electrowetting on dielectric actuation of droplets with capillary electrophoretic zones for MALDI mass spectrometric analysis

An automated fraction collection interface was developed for coupling CE with MALDI-MS. This fraction collection approach is based on the electrowetting on dielectric (EWOD) phenomenon performed on a digital microfluidic (DMF) board; it does not rely on a MALDI spotter. In this study, a four-peptide mixture was used as a sample test, and the separations were conducted in a portable CE instrument with a 150 μm o.d. × 50 μm i.d. capillary and a contactless conductivity detector. The CE instrument was interfaced with a robust DMF board. The CE fractions were directly deposited onto the DMF board at predetermined locations prior to MALDI analysis. The series of experiments determined the lowest concentration that produces a measurable MALDI signal. The concentrations were 0.25, 0.5, 0.05, and 0.05 nmol for bradykinin, angiotensin, ACTH (18-39), and insulin, respectively. The contactless conductivity detector limit of detection for the same analytes was 2.5 μmol.