Laser Electrospray Mass Spectrometry
LEMS
 

The objective of our research is to develop a new type of ambient mass spectrometric technique combining nonresonant fs laser vaporization and electrospray ionization. The two methods combined allows for the vaporization of neutral sample molecules using the nonresonant fs laser and post-ionization using the electrospray. Using laser electrospray mass spectrometry, LEMS, we have successfully analyzed explosives, pharmaceuticals, large biomolecules and tissue.

 

Laser Electrospray Mass Spectrometry (LEMS) in an ambient environment

  • LEMS is a combination of nonresonant femtosecond laser vaporization and electrospray post-ionization.
  • Neutrals are vaporized from a sample surface using a femtosecond laser.
    • Femtosecond laser vaporization produces more neutral molecules than nanosecond laser desorption due to the ultrashort pulse duration.
  • The neutrals are captured in the electrospray plume where they undergo ionization.
  • The ions then travel to the inlet of the mass spectrometer for mass analysis and detection.
 

LEMS of Vitamin B12

Vitamin B12
 

A 250 mL aliquot of 10-3 M vitamin B12 was spotted and dried on a glass slide and analyzed using LEMS. The acquired mass spectrum shows the protonated molecular ion at m/z 1356. The doubly charged ion is also observed demonstrating that electrospray ionization is the dominante mechanism. This is the first demonstration of matrix-free vaporization of neutral molecules at atmospheric conditions with a nonresonant femtosecond laser.

 
LEMS of Human Blood
Human Blood
 

Human blood deposited on a metal slide was subjected to LEMS analysis. Multiple charging of hemoglobin subunits (a and b hemoglobin subunits are indicated by the square and circle symbols, respectively) indicates electrospray ionization is the dominante mechanism. In addition to the a and b hemoglobin subunits, the b heme is also present in the mass spectrum. We have demonstrated, using femtosecond laser pulses, that the vaporization of intact molecules up to 16,000 Da under ambient conditions is possible.

     
Image Reconstruction using LEMS

A 50 mL aliquot of 10-5 M oxycodone was spotted and dried on a stainless steel slide and analyzed using LEMS. A typical mass spectrum from red spots on the reconstructed image shows protonated adduct of oxycodone at m/z 316. No oxycodone is observed in the light gray spectrum which is consistent with the black areas on the reconstructed image. Inset pictures show before and after LEMS analysis of oxycodone.

 
LEMS Publications
Brady, J.J., Judge, E.J., and Levis, R.J., Mass spectrometry of intact neutral macromolecules using intense non-resonant femtosecond laser vaporization with electrospray post-ionization, Rapid Commun. Mass Spectrom., 23: 3151-3157 (2009).
Brady, J.J., Judge, E.J., and Levis, R.J., Identification of Explosives and Explosive Formulations Using Laser Electrospray Mass Spectrometry, Rapid Commun. Mass Spectrom., 24: 1-6 (2010)
 
 
 
 
Brady, J.J., Judge, E.J., Levis, R.J., Nonresonant Femtosecond Laser Vaporization of Aqueous Protein Preserves Folded Structure, P. Natl. Acad. Sci. USA, Accepted, (2011)

 

Levis Group, Department of Chemistry, Temple University, Beury Hall 244, 1901 N. 13th Street, Philadelphia, PA 19122    Tel: 215-204-5241     Fax: 215-204-6179
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