Experimental Methods

We are developing tools and techniques to probe the physical characteristics and chemical composition of levitated droplets exposed to environmental conditions that mimic the natural atmosphere.

Linear array of particles in LQ-EDB

Droplet Levitation

A linear-quadrupole electrodynamic balance is used to levitate particles in a linear array. Vertical forces are balanced with an electrostatic force indicating the mass response of a droplet to changing conditions. Particles are illuminated by laser and produce a scattering pattern.

Light scattering pattern from a spherical droplet

Mie resonance spectroscopy allows the size and optical properties of spherical droplets to be determined.

Mie Resonance Spectroscopy

A levitated droplet is illuminated by broadband light from and LED and the back-scattered light is sampled with a spectrometer. Wavelengths of light that are resonant in the droplet are scattered more efficiently and produce intense peaks in the spectrum that allow the size and refractive index to be determined. Light absorbing droplets show characteristic deviations from this behavior.

Single Particle Mass Spectrometry

Methods are being developed to sample droplets from the LQ-EDB to determine composition using high resolution mass spectrometry. The current approach leverages an open-port sampling interface that collects single particles from the LQ-EDB and delivers them to the electrospray ionization source of our Orbitrap mass spectrometer. This method softly ionizes analytes and allows for sensitivity down to picogram levels.

OPSI interface positioned at the outlet of the the LQ-EDB collects single particles and delivers them to the ESI source of our MS.

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