Generating electrospray from solutions predeposited on a copper wire

This study presents a novel direct probe (DP) to perform electrospray ionization (ESI). The probe is constructed simply from a thin copper ring connected to a high voltage power supply, and a capillary and syringe pump are unnecessary. Approximately one microliter of the sample solution is applied directly onto the copper ring by a micropipette. Electrospray from the solution on the copper ring is induced by surface deformation by deflecting a droplet from the copper ring. The mass spectra of proteins obtained by DP–ESI are exactly the same as those from conventional ESI sources through a capillary needle. The time deemed necessary to complete an analysis is approximately 2 minutes, and sample switching is immediate. The signals of the analyte can last from 45 seconds to more than 10 minutes depending on probe design. Three different types of probes used to retain more sample solution on the probe during electrospray were designed and constructed. Moreover, cleaning the probe between different sample analysis is easy. Since a capillary is not used for sample transportation, presence of the particles in the sample solution does not interfere with the electrospray process by capillary blockage. Copyright © 1999 John Wiley & Sons, Ltd.