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.