Single-pulse nanoelectrospray ionization.

A new electrospray ionization (ESI) source that provides a means of generating single packets of ions for mass spectrometric analysis is presented. Sample solution held at a high potential is ejected from a glass capillary with a small dispensing aperture (20-microm i.d.) by constriction of a cylindrical piezoelectric element. Unlike conventional ESI sources that are continuous, this source dispenses fixed volumes of solution as small as 10 pL and provides detection sensitivity in the attomole range when coupled to an orthogonal time-of-flight mass spectrometer. In addition to picoliter-level control over the dispensed volume, the source permits control of the frequency with which ionization pulses are generated as well as the ability to start and stop the pulses without altering the applied solution potential. The source was characterized by analysis of both protein and DNA samples from a variety of different solution compositions. This source design should be compatible with virtually any ESI mass analyzer.