Modified liquid junction interface for nonaqueous capillary electrophoresis-mass spectrometry

Electrospray ionization (ESI) is the most widely used ionization method in on-line coupling of capillary electrophoresis-mass spectrometry (CE-MS). Th e conventional coaxial sheath flow electrospray interface is currently bein g replaced by the more sensitive nanoelectrospray technique. The usual limi tation of nanoelectrospray CE-MS interface has been its short lifetime caus ed by deterioration of the metal coating on the CE capillary terminus. This article describes an easy way to construct a more durable and sensitive na nospray interface for nonaqueous CE-MS. In this approach a very thin glass spray capillary (ca. 30 mu m outer diameter) is partly inserted inside the CE capillary, the junction being surrounded by the electrolyte medium, whic h is in contact with the platinum electrode. The interface was tested with five pharmaceuticals: methadone, pentazocine, levorphanol, dihydrocodeine, and morphine. Detection limits ranged from 12 to 540 fmol. Separation effic iency and reproducibility were also studied. The CE current was found to be stable and the migration times were highly reproducible. All the CE separa tions were carried out in a nonaqueous background electrolyte solution.