Two-Step Laser Desorption Time-of-Flight Mass Spectrometer

Two-Step Laser Desorption Time-of-Flight Mass Spectrometer

Through a NASA Space Technology Research Fellowship, I have had the opportunity to work with Dr. Stephanie Getty at NASA Goddard Space Flight Center to explore the optimization of a two-step laser desorption time-of-flight mass spectrometer (L2MS) for the detection of organic molecules and other biosignatures. The L2MS separates the desorption and ionization functions of laser desorption/ionization mass spectrometry into two distinct laser pulses to provide selectivity to key subclasses of organic species, such as aromatic hydrocarbons. The use of distinct laser wavelengths allows efficient coupling to the vibrational and electronic spectra of the analyte in independent desorption and ionization steps, allowing for the mitigation of excess energy that can lead to fragmentation during the ionization process.

An annotated photograph of the L2MS with a schematic demonstrating the geometry of the IR desorption and UV ionization lasers.

IR Resonance Desorption

I have focused my efforts on characterizing the L2MS desorption IR laser wavelength dependence on organic detection sensitivity in an effort to optimize the detection of high mass (>100 Da) organic peaks. We analyze samples with an IR spectrometer using an acousto-optic tunable filter (AOTF) as the dispersive element, and an L2MS with a tunable desorption IR laser whose wavelength range (2.7-3.1 microns) overlaps that of the AOTF IR spectrometer (1.6-3.6 microns). A correlation between the maximum absorption of the organic functional groups and broad hydration features - inferred from the IR spectrum - and the optimal IR laser configuration for organic detection using L2MS indicates that IR spectroscopy may be used to inform the optimal L2MS IR laser wavelength for organic detection.

We have measured synthetic organic mixtures including organically doped sulfate slurries, meteoritic powders, icy body analogs (at -100C), and field samples to identify the organic detection limits of the L2MS and to characterize the mineral matrix dependence on organic desorption.

This figure shows the dependence the desorption laser wavelength has on the L2MS detection sensitivity of the aromatic amino acid tryptophan. We prepared a slurry of epsomite doped with 0.1wt% tryptophan. Pure epsomite and tryptophan powders were measured with the AOTF IR spectrometer to identify hydration and organic functional group absorption features (top panel: red - tryptophan; blue - epsomite). Epsomite is expected to retain its structurally bound water over geologic time periods under Europa surface conditions, making it an ideal icy body analog for our laboratory studies focusing on the desorption of hydration features in vacuum. The mass spectrum of this synthetic mixture shows an increased signal associated with an IR desorption laser wavelength tuned to IR spectral features. At 2935 nm, the detection of the primary tryptophan fragment (C10H11N) is maximized, corresponding closely with the vibrational transition of the NH functional group.

Relevant Peer-Reviewed Publications

A complete publication list is available in my CV and Google Scholar profile.

K. Uckert, S. Getty, A. Grubisec, X. Li, W. B. Brinckerhoff, N. J. Chanover. IR Resonance Enhanced Organic Detection with a Two-Step Laser Desorption Time-of-Flight Mass Spectrometer. In Preparation.

K. Uckert, S. A. Getty, N. Chanover, X. Li, W. B. Brinckerhoff, T. Cornish, D. Voelz, X. Xiao. IR Spectroscopy and Two-Step Laser Desorption/Ionization Time-of-Flight Mass Spectrometry as a Biosignature Identification Instrument Suite. Astrobiology Science Conference, Abstract #7607, Chicago, IL, June 2015.

X. Li, K. Uckert, S. Getty, A. Grubisic, W. Brinckerhoff, T. Cornish, S. Ecelberger, N. Chanover. Analysis of Aqueous Environments by Laser Desorption/Ionization Time-of-Flight Mass Spectrom- etry. 63rd American Society for Mass Spectrometry (ASMS) Conference on Mass Spectrometry and Allied Topics, St. Louis, MO, May 2015.

K. Uckert, S. Getty, A. Grubisic, X. Li, W. Brinckerhoff, T. Cornish, N. Chanover, J. E. Elsila, R. Zare. A Demonstration of the Organic Detection Capabilities of a Two Step Laser Desorp- tion/Ionization Time-of-Flight Mass Spectrometer. 63rd American Society for Mass Spectrometry (ASMS) Conference on Mass Spectrometry and Allied Topics, St. Louis, MO, May 2015.

S. A. Getty, X. Li, A. Grubisic, K. Uckert, T. Cornish, J. E. Elsila, M. P. Callahan, W. B. Brinckerhoff. Two-Step Resonance-Enhanced Desorption Laser Mass Spectrometry for in situ Analysis of Organic-Rich Environments. Lunar and Planetary Science Conference, Vol. 46, Abstract #2231, The Woodlands, TX, March, 2015.

X. Li, K. Uckert, S. Getty, A. Grubisic, W. Brinckerhoff, T. Cornish, S. Ecelberger, N. Chanover. Analysis of aqueous environments by laser desorption/ionization time-of-flight mass spectrometry. Aerospace Conference, 2015 IEEE, pp 1-10, March 2015.

S. A. Getty, W. B. Brinckerhoff, X. Li, A. Grubisic, K. Uckert, T. Cornish, A. E. Southard, M. Balvin, J. Ferrance, J. E. Elsila, M. P. Callahan, P. R. Mahaffy. Time-of-Flight Mass Spectrometry for in situ Analysis of Biosignatures at Europa. Workshop on the Potential for Finding Life in a Europa Plume, Pasadena, CA, February, 2015.

K. Uckert, N. J. Chanover, S. Getty, A. Grubisic, X. Li, W. B. Brinckerhoff, T. Cornish, D. Voelz, X. Xiao, D. Glenar. Using IR Spectroscopy to Optimize Organic Detection with a Two-Step Laser Desorption/Ionization Time-of-Flight Mass Spectrometer. International Workshop on Instrumentation for Planetary Missions, Abstract #1113, Greenbelt, MD, November, 2014.

S. A. Getty, X. Li, T. Cornish, A. Grubisic, K. Uckert, J. Elsila, W. B. Brinckerhoff, Q. Wu, R. N. Zare. A Two-Step Tandem Laser Time-of-Flight Mass Spectrometer for the in situ Study of the Surfaces of Primitive and Icy Solar System Bodies. International Workshop on Instrumentation for Planetary Missions, Abstract #1101, Greenbelt, MD, November, 2014.

K. Uckert, N. J. Chanover, S. Getty, W. B. Brinckerhoff, D. G. Volez, N. McMillan, X. Xiao, X. Li, M. Floyd, P. J. Boston. The Identification of Biosignatures on Planetary Surfaces from in situ Techniques, Including Miniaturized Mass Spectroscopy. 62rd American Society for Mass Spectrometry (ASMS) Conference on Mass Spectrometry and Allied Topics, Baltimore, MD, June 2014.