Transcript DESI - plaza

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.