Mass Spectrometry of Levitated Droplets by Thermally Unconfined Infrared-Laser Desorption

Abstract

An ionization scheme for fast online mass spectrometric interrogation of levitated droplets is presented. That renewed method comprises the output of an a Er:YAG laser at λ = 2.94 μm which is in resonance with the OH stretch vibration band of solvents like water and alcohols. A temporal pulse width larger than the time needed for pressure redistribution and also above the temperature redistribution time constant was found to lead to soft evaporation/ionization. Despite these mild desorption conditions, no additional postionization is found to be needed. Accordingly, the ionization is found to be very soft resulting in entirely intact analyte ions and concentration dependent cluster ions. Resulting mass spectra of small amino acids and large antibiotics are presented showing the versatility of the introduced technique. Above a critical mass of m ≈ 1 kDa, the formed ions carry multiple charges as it is typical for thermospray or electrospray ionization. The detection technique enables fast contactless analysis of the chemical composition of levitated microreactors and, thus, paves the way for future contactless reaction monitoring.

Real Time Monitoring of Containerless Microreactions in Acoustically Levitated Droplets via Ambient Ionization Mass Spectrometry

“…Analyte characterization was carried out offline via matrix-assisted laser desorption ionization (MALDI)-TOF and gel permeation chromatography (GPC). In addition, Stindt et al and Warschat et al combined laser ablation (using CO 2 and IR lasers) with TOF mass spectrometry to directly analyze liquid samples in a containerless environment.…”

Electrodynamic balance–mass spectrometry of single particles as a new platform for atmospheric chemistry research

“…Modification of the ionization scheme may also be necessary to obtain sufficient signal when working with smaller particles or analyte compounds present in smaller quantities. One approach may be to vaporize the particle not with a heated platform, but with an infrared laser, possibly followed by a separate gas-phase ion source (as in Warschat et al, 2015;Westphall et al, 2008;or Zelenyuk et al, 2009). Alternately, an electrospray-type scheme may be used, such as delivering the particle onto a paper spray source (as in Jacobs et al, 2017), ionizing via an interaction between the particle and a spray of ions (e.g., as in Doezema et al, 2012;Gallimore and Kalberer, 2013;or Horan et al, 2012), or by producing a spray directly from the particle when dropped onto a charged needle tip (as in Tracey et al, 2014).…”

“…Additionally, in a different laboratory a quadrupole ion trap mass spectrometer was modified to levitate individual micron-sized droplets, followed by reducing the trap pressure over 20 min to ∼ 0.1 Pa, ablating the particle with a pulsed laser (532 nm), and collecting a mass spectrum using the same ion trap (Yang et al, 1995). Previous work has also reported measuring mass spectra of aqueous droplets suspended in acoustic traps (Crawford et al, 2016;Stindt et al, 2013;Warschat et al, 2015;Westphall et al, 2008). The aqueous droplets suspended in acoustic traps tend to have a diameter on the order of a millimeter, much larger than the micron or submicron diameter of atmospheric aerosol particles.…”

High-throughput platforms for metabolomics

“…Another matrix-free, desorption methodis levitated droplet-MS [57]. This technique uses a laser for the ionization and desorption ofacoustically levitated droplets.…”