Electrospray sample deposition for matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure MALDI mass spectrometry with attomole detection limits

Rapid Commun Mass Spectrom. 2004;18(11):1193-200. doi: 10.1002/rcm.1458.


Electrospray sample deposition was explored for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). In this method, nanoliter volumes of matrix/analyte mixture were electrosprayed from a high voltage biased (1-2 kV) fused-silica capillary onto a grounded MALDI plate mounted 100-500 microm from the capillary outlet. Electrospray deposition with these conditions produced sample spots 200-300 microm in diameter thus matching the laser spot size. Varying spray voltage and distance resulted in different crystal sizes and volatilization rates for alpha-cyano-4-hydroxycinnamic acid matrix. Best results were obtained when the sample was deposited as wet droplets as opposed to deposition as dried solid. Under 'wet-spray' conditions, 2-4 microm diameter crystals were formed and detection limits for several neuropeptides were 0.7-25 amol. Samples could be pre-concentrated on the plate by spraying continuously and allowing sample to evaporate in a small spot. Sample volumes as large as 580 nL were deposited yielding a detection limit of 35 pM for neurotensin 1-11. Electrospray sample deposition yielded similar results when using atmospheric pressure-MALDI coupled with a quadrupole ion trap mass spectrometer, except that the sensitivity was approximately seven-fold worse.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Atmospheric Pressure*
  • Neuropeptides / analysis*
  • Sensitivity and Specificity
  • Spectrometry, Mass, Electrospray Ionization / methods*
  • Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / methods*


  • Neuropeptides