ambient mass spectrometry using desorption electrospray ionization (desi) farzad fani pakdel group...
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Ambient mass spectrometry using
Desorption Electrospray Ionization (DESI)
Farzad Fani Pakdel
Group meetingThursday March 23, 2006
Summary
About DESI
Normal experimental conditions
Some applications
DESI and DART
Advantages
Ambient mass spectrometry
http://www.jeolusa.com/ms/msprods/accutof_dart.htmlRobert Cody at Jeol USA, Inc, MA
TOF
No sample preparation
Fast analysis
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 L/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 monitoringAnalysis of Blood and Urine
Tissue imaging
RDX = 222 g / mol
CF3 COOH
TFA = 114 g / mol
Example: Explosive detection
1ng of RDX on 1 mm2 of leatherCommercial ion trap usedNegative mode
M-1
P
O
Me
O O
Me Me
Mw = 124
DMMP chemical warfare agents simulant (simulate or stimulate)
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!!!!!
REFRENCESDESI 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.