High-pressure ESI-MS made easy using a plug-and-play ion source and its application to highly conductive aqueous solutions.

The performance of a compact high-pressure electrospray ionization (HP-ESI) source that can be readily used for commercial atmospheric pressure ionization (API) mass spectrometers is reported. The ion source employs a converging-diverging outlet nozzle, and ions/droplets generated inside the high-pressure compartment are carried by the high-velocity air jet toward the mass spectrometry (MS) ion inlet placed under the atmospheric pressure. With the use of a shielding electrode, the HP-ESI can also be operated with its emitter held at ground potential. This feature prevents the flow of current from the emitter to other electrically grounded components and facilitates the connection of ion source to liquid chromatography (LC) columns or capillary electrophoresis. Sensitive detection of proteins from highly conductive aqueous solutions such as 0.1% trifluoroacetic acid (TFA) solution and the prevention of electrochemical artifacts by the grounded emitter operation are demonstrated.