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Ambient mass spectrometry using Desorption Electrospray Ionization (DESI) Farzad Fani Pakdel Group meeting Thursday March 23, 2006 Summary About DESI Normal experimental conditions Some applications DESI and DART Advantages Ambient mass spectrometry No sample preparation Fast analysis TOF http://www.jeolusa.com/ms/msprods/accutof_dart.html Robert Cody at Jeol USA, Inc, MA About DESI Reported in 2004 by R. Graham Cooks, Purdue University, IN Combination of ESI and DI (SIMS or Laser Desorption) Charged droplets and ions of solvent are sprayed onto the sample for ionization Water or water-Methanol spray on a surface It is a soft ionization technique Large and small molecules: Amino acids, drugs, alkaloids, terpenoids and steroids, peptides and proteins on metal, polymer (PTFE) and mineral surfaces INSTRUMENTATION Experimental Condition Sample is on PTFE (PolytetrafluoroEthylene) surface 1-1 water-methanol was used as spray solvent, 0.1% TFA Flow rate 3-15 mL/min The High voltage = 4 kV Nominal velocity of nebulizing gas = 350 m / s Capillary inlet-sample distance 2 mm Tip-sample distance 5 mm Incident angle (α) 50 degrees Collection angle (β) 10 degrees Applications of DESI Large variety of applications like other MS methods Particularly promising for forensic and public safety applications: Detection of Explosives Chemical warfare monitoring Analysis of Blood and Urine Tissue imaging Example: Explosive detection RDX = 222 g / mol TFA = 114 g / mol CF3 COOH 1ng of RDX on 1 mm2 of leather Commercial ion trap used Negative mode M-1 DMMP chemical warfare agents simulant (simulate or stimulate) O Me Me O P O Me Mw = 124 DESI of nitrile gloves exposed to DMMP vapor for less than one second and then washed Limit of detection for explosives Skin of a Fruit (tomato!!!) Large non-polar molecules Movement of tip and sample Tissue imaging Certain phospholipids in liver DESI or DART? DESI vs. DART 1-5 KV +- 100 V 5-25 mm Advantages of DESI Ambient condition Large range of molecules from small to proteins Sample can be moved in space during analysis (Imaging) No need for Matrix unlike MALDI Multiple charge ions is an advantage to extend mass range (proteins) Variable distance and angel allows different energy levels and makes it proper for a wider range of molecules (Proteins) Reactant molecules (TFA) can be sprayed to enhance ion complex formation Disadvantage ------- uses solvent!!!!! REFRENCES DESI by Cooks: (26 out of 35) Science. 2006 ; Vol. 311,1566 - 1570 J. Mass Spectrom. 2005; 40: 1261–1275 Anal. Chem. 2005, 77, 6915-6927 Science. 2004; Vol. 306, 471-473 DART: Robert B. Cody, James A. Laramee, and H. Dupont Durst, Anal. Chem. 2005, 77, 2297-2302.