Electrospray ionization (ESI) is a technique used in mass spectrometry to produce ions from a liquid by applying a high voltage to create an aerosol spray. The ESI process involves dispersing a fine spray of charged droplets, followed by solvent evaporation and ion ejection from highly charged droplets. ESI is a soft ionization technique that allows intact ions of large molecules like proteins to be transferred from solution to the gas phase. It was developed in the late 1980s and was recognized with the 2002 Nobel Prize in Chemistry awarded to John Fenn.

1. 02/28/16
1
Submitted by:
Mo hit Kumar Verma
(Pharmaco lo gy 1 st
Year)
Dept. o f PharmaceuticalScience

2. 02/28/16 2
Electrospray ionization (ESI) is a technique used in mass
spectrometry to produce ions using an electrospray in which a
high voltage is applied to a liquid to create an aerosol.
The transfer of ionic species from solution into the gas phase
by ESI involves three steps:
(1) Dispersal of a fine spray of charge droplets, followed by
(2) Solvent evaporation and
(3) Ion ejection from the highly charged droplets.

3. 02/28/16
3
The first use of electrospray ionization with mass spectrometry
was reported by Malcolm Dole in 1968.
John Bennett Fenn was awarded the 2002 Nobel Prize in
Chemistry for the development of electrospray ionization mass
spectrometry in the late 1980s.

4. DEFINITION
Electrospray:
An electrical nebulization of liquid that results in the
formation of charged micro droplets
Electrospray ionization:
The transfer and ionization of molecules from solution to gas
phase by electrospray are called Electrospray ionization.
02/28/16 4

5. Intrumentetion and ESI key features:
02/28/16 5
 Capillary (LC) 90o
to Cone (MS) .
 Nebulized flow through capillary
 Heat applied to evaporate solvent
 Voltage difference applied between capillary and cone

6. Ionization Mechanism in ESI
02/28/16
6
1) Coulomb Fission:
Assumes that the increased charge density, due to solvent
evaporation, causes large droplets to divide into smaller
droplets eventually leading to single ions.
2) Ion Evaporation:
Assumes the increased charge density that results from solvent
evaporation causes Coulombic repulsion to overcome the
liquid’s surface tension, resulting in a release of ions from
dropletsurfaces
(1)
(2)

7. February 28, 2016
7
Pressure and
Electrical potential gradient
coaxial nebulization
gas flow
Countercurrent gas flow
to aid desolvation

8. ESI Advantages
02/28/16
8
Soft-ionization technique
Controllable fragmentation
Readily coupled to liquid separations
Produces intact non-covalent complexes
Multiple-charging of analyte
Capable of ionizing large molecules (to MDa)

9. Disadvantages of ESI
02/28/16 9
Analyte must have an acidic or basic site
e.g.Hydrocarbons and steroids not readily ionized by ESI
Analyte must be soluble in polar, volatile solvent
ESI is less efficient than other sources
ESI is very sensitive to contaminants
Distribution of multiple charge states can make
spectra of mixtures hard to interpret
e.g. polymer mass spectra

10. Applications
 The adjacent peaks of a series differ by only one
charge
 For proteins, the charging is due to proton attachment
to the molecular ion.
 This has been an excellent (but not crucial)
assumption of nearly all proteins studied to data
where alkali attachment contributions are small.
 Ionization of only the intact molecule.
02/28/16 10

11. OTHER IONIZATION TECHNIQUES
02/28/16 11
Ionization Method Typical
Analytes
Sample
Introduction
Mass
Range
Method Highlights
Electron Impact (EI) Relatively small.
Volatile.
GC or liquid
or solid probe
To 1000
Daltons
Hard method.
Provides structural info
Chemical Ionization
(CI)
Relatively small.
Volatile.
GC or liquid
or solid probe
To 1000
Daltons
Soft method. Molecular
ion peak [M+H]+
Electrospray (ESI) Peptides/proteins.
Non-volatile.
Liquid
Chromatography
To 200,000
Daltons
Soft method. Ions often
multiply charged.
Matrix Assisted Laser
Desorption (MALDI)
Peptides/proteins.
Non-volatile.
Sample mixed in
solid matrix
To 500,000
Daltons
Soft method.
Very high mass range.
Fast Atom
Bombardment (FAB)
Carbs/peptides.
Non-volatile.
Sample mixed in
viscous matrix
To 6000
Daltons
Soft method, but harder
than ESI or MALDI

12. ANY……
02/28/16 12

13. 02/28/16 13
1. Spectrometric Identification of Organic Compounds, 7th
ed,
Silverstein, Webster, and Kiemle, John Wiley and Sons, 2005
2. Hogan, C. J., Carroll, J. A., Rohrs, H. W., Biswas, P., Gross, M.
L., Anal. Chem., 2009, 81 (1), pp 369–377
3. Ifa, R. I., Manicke, N. E., Dill, A. L., Cooks R. G.; Science,
2008, 321, 805
4. Cooks, R. G., Ouyang, Z., Takats, Z., Wiseman, J. M.; Science,
2006, 311, 1566
5. Kelesidis, T., Kelesidis, I., Rafailidis, P. I., Falagas, M. E.;
Journal of Antimicrobial Chemotherapy, 2007, 60, 214–236
6. Esquenazi, E., Pieter C. Dorrestein P. C., and Gerwick, W. H.;
PNAS, 2009, 106(18), 7269–7270
References