title: Electrospray sample deposition for matrix-assisted laser desorption/ionization (MALDI) and atmospheric pressure MALDI mass spectrometry with attomole detection limits.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Wei
authors.forename: Kerstin
authors.initials: K
authors.lastname: Nolkrantz
authors.forename: David H
authors.initials: DH
authors.lastname: Powell
authors.forename: James H
authors.initials: JH
authors.lastname: Woods
authors.forename: Mei-Chuan
authors.initials: MC
authors.lastname: Ko
authors.forename: Robert T
authors.initials: RT
authors.lastname: Kennedy
mesh_terms: D001274:Atmospheric Pressure; D009479:Neuropeptides / Q000032:analysis*; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D009479:Neuropeptides