The development of a two-leveled two cross interface for on-line coupling solid-phase extraction and capillary electrophoresis-mass spectrometry.

A two-leveled, two cross PDMS-based interface for on-line coupling of SPE with CE-MS was proposed. In this interface, the SPE column and the CE separation column were positioned orthogonally and two crosses were fabricated on the interface. With the two cross design, the operation of SPE could be performed independently without unexpected flow through leakage into the separation column. The performance of the interface was optimized using a peptide mixture. The position of the SPE column related to the CE separation channel was found to be critical to the performance of the system. Under the optimal position, the separation efficiency was similar to a CE-MS experiment without SPE. The peptide signals were enhanced 50- to 100-fold and the repeatability was within 4% RSD for migration time and 10% RSD for peak area. A tryptic digest of cytochrome c was used to demonstrate the feasibility of the interface in protein identification at a level of 1 ng/microL.