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 (P-E) overwhelms the inward pressure 137 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 mu m i.d. glass capillary. Multiply protonated ions for all three samples started to be detected with the 300 ys pulse width. Denaturation of C and U proceeded with an increase of the pulse width. When the bias voltage of similar to 880 V that was lower than the threshold voltage for the generation of continuous electrospray (similar to 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 mu s to regenerate electrospray.