Ambient mass spectrometry using Desorption Electrospray Ionization DESI

Ambient mass spectrometry using Desorption Electrospray Ionization (DESI) Farzad Fani Pakdel Group meeting Thursday March 23, 2006

Summary ØAbout DESI ØNormal experimental conditions ØSome applications ØDESI and DART ØAdvantages

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 Ø Reported in 2004 by R. Graham Cooks, Purdue University, IN ØCombination of ESI and DI (SIMS or Laser Desorption) ØCharged droplets and ions of solvent are sprayed onto the sample for ionization ØWater or water-Methanol spray on a surface Ø It is a soft ionization technique ØLarge and small molecules: Amino acids, drugs, alkaloids, terpenoids and steroids, peptides and proteins Øon metal, polymer (PTFE) and mineral surfaces

INSTRUMENTATION

Experimental Condition ØSample is on PTFE (Polytetrafluoro. Ethylene) surface Ø 1 -1 water-methanol was used as spray solvent, 0. 1% TFA ØFlow rate 3 -15 m. L/min ØThe High voltage = 4 k. V ØNominal 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 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 CF 3 COOH

1 ng of RDX on 1 mm 2 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 ØAmbient condition ØLarge range of molecules from small to proteins ØSample can be moved in space during analysis (Imaging) ØNo need for Matrix unlike MALDI ØMultiple charge ions is an advantage to extend mass range (proteins) ØVariable distance and angel allows different energy levels and makes it proper for a wider range of molecules (Proteins) ØReactant 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.