Electrospray current measurement in the nanospray and microspray regime

A method of electrospray ionization of a fluid sample, wherein an electrospray assembly includes a fluid union, a fluid column coupled with a first port, a power source coupled with the fluid union and the first port and configured to apply a voltage to the fluid union sufficient to ionize the fluid sample to form an ionized fluid sample, an electrospray emitter coupled with the fluid union, and a current sensing circuit disposed between the power source and the fluid union, the method comprising:

• separating molecules in the fluid sample using the fluid column to produce a separated fluid sample;
• transferring the separated fluid sample into the fluid union via the first port,
• applying the voltage to the fluid union and to the first port, the voltage at the fluid union and first port being balanced to restrict current leakage from the fluid union;
• via the current sensing circuit, measuring an electrical current flow between the power source and the fluid union.

An apparatus for electrospray ionization of a fluid sample, wherein the apparatus includes a fluid union, a fluid column coupled with a first port, and an electrospray emitter coupled with the fluid union, wherein the fluid column is configured to separate molecules in the fluid sample to produce a separated fluid sample and to transfer the separated fluid sample into the fluid union via the first port, the apparatus comprising:

• a power source configured to apply a voltage potential to the fluid union sufficient to ionize the fluid sample to form an ionized fluid sample, wherein the power source is further configured to apply the voltage potential to the first port to restrict current leakage from the fluid union;
• a current sensing circuit configured to determine an electrical current flow between the power source and the fluid union;
• and
• a controller configured to determine an electrospray operation regime based on the electrical current flow.