ELECTROHYDRODYNAMIC PULSATION OF THE TAYLOR CONE

We showed that Taylor cone deformations play a central role in the mechanism of electrostatic spraying. Spontaneous spray current oscillations are known to exist in most electrospray regimes and affect the stream of ions introduced into the mass spectrometer. Fast time-lapse imaging of the Taylor cone throughout its evolution (see the movie on the right) indicates the presence of a nodal line and standing waves on its surface. Four phases of the cone pulsation cycle are established:

  • liquid accumulation
  • cone formation
  • jet ejection
  • relaxation

Based on image analysis, apex velocities, curvatures and opening angles were determined. During jet ejection, the apex velocity and the curvature exhibit singularities. Furthermore, the pulsation frequencies of the Taylor cone deformations are determined using Fourier analysis of light refraction measurements. The oscillation frequency of the electrospray current collected by the counter electrode shows close correlation to the cone deformations, providing the first direct evidence that links spray current oscillations to Taylor cone pulsation.

We suggest two possible applications of these observations:

  • Monitoring the oscillation frequency throughout the spraying process and adjusting the spray parameters can be used to stabilize the spray.
  • Synchronizing the injection of ions in time-of-flight systems with the spontaneous spray oscillations may improve the signal-to-noise ratio in the collected mass spectra.

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Last update: November 14, 2006