Pulsed Nano-Electrospray Ionization with a High Voltage (4000 V) Pulse Applied to Solutions in the Range of 200 ns to 1 ms.

To initiate electrospray, it is necessary to accumulate excess charges on the liquid surface until the outward electrostatic pressure (PE) overwhelms the inward pressure Pγ originating from the surface tension of the liquid droplet. In this report, electrospray mass spectrometry for solutions of gramicidin S (G), ubiquitin (U), and cytochrome c (C) in H2O/CH3OH (1/1) was performed as a function of the high voltage (4000 V) pulse width in the range of 200 ns to 1 ms using a 4 μm i.d. glass capillary. Multiply protonated ions for all three samples started to be detected with the 300 μs pulse width. Denaturation of C and U proceeded with an increase of the pulse width. When the bias voltage of ∼880 V that was lower than the threshold voltage for the generation of continuous electrospray (∼1000 V) was applied to the solution, multiply protonated G, U, and C were detected with the 200 ns pulse width. After the depletion of excess charges in 200 ns, it took 10-100 μs to regenerate electrospray.