System for minimizing electrical discharge during ESI operation

A mass spectrometer system, comprising:

• a liquid chromatography (LC) column for providing a liquid sample to be analyzed;
• an electrospray ion source in fluid communication with the LC column, the electrospray ion source comprising:
• an ion source housing defining an ionization chamber;
• at least one heater for heating the ionization chamber;
• an electrospray electrode defining an axial bore therethrough for transmitting a liquid sample received from a sample source at an inlet end of the electrospray electrode to an outlet end for discharging the liquid sample from the electrospray electrode into the ionization chamber;
• and
• a mass analyzer for analyzing the ions generated by the ion source, wherein the ions are received by the mass analyzer through a sampling orifice in a counter electrode, the sampling orifice being in fluid communication with the ionization chamber;
• a power source configured to provide an electrical voltage to an electrical circuit containing the electrospray electrode and the counter electrode so as to generate an ion emission current between the electrospray electrode and the sampling orifice as at least a portion of the liquid sample is ionized upon being discharged from the electrospray electrode;
• and
• the ion emission current configured to prevent arcing between the electrospray electrode and the counter electrode without substantially altering the electrical voltage provided to the electrical circuit by the power source, by:
• a shunt electrode disposed between the LC column and the outlet end of the electrospray electrode, the shunt electrode configured to be in electrical communication with the liquid sample, wherein at least a portion of the electrical current between the power source and the electrospray electrode is diverted to the shunt electrode based on the conductivity of the portion of the liquid sample between the outlet end of the electrospray electrode and the shunt electrode.

A method for operating an electrospray ion source of a mass spectrometer system, the method comprising:

• transmitting a liquid sample from an inlet end of an electrospray electrode to an outlet end of the electrospray electrode, the outlet end being disposed in an ionization chamber so as to discharge the liquid sample from the outlet end of the electrospray electrode into the ionization chamber, the ionization chamber being in fluid communication with a sampling orifice formed in a counter electrode of a mass spectrometer system;
• heating the ionization chamber;
• operating a power source to provide an electrical voltage (electromotive force) to an electrical circuit containing the electrospray electrode and the counter electrode so as to generate an ion emission current between the electrospray electrode and the sampling orifice as at least a portion of the liquid sample is ionized upon being discharged from the electrospray electrode;
• and
• controlling the ion emission current so as to limit the onset of electrical discharge between the electrospray electrode and the counter electrode without substantially altering the electrical voltage provided to the electrical circuit by the power source, by:
• providing a shunt electrode disposed between an LC column and the outlet end of the electrospray electrode, the shunt electrode configured to be in electrical communication with the liquid sample, wherein at least a portion of the electrical current between the power source and the electrospray electrode is diverted to the shunt electrode based on the conductivity of the portion of the liquid sample between the outlet end of the electrospray electrode and the shunt electrode.