278
Electro-Spray Ionization Mass Spectrometry (ESI-MS)
This is a “soft ionisation“technique that enables the analysis of large intact (underivatised) biomolecules, such as proteins and DNA. It involves atomisation of
solvent containing analyte into a spray of charged liquid droplets at an atmospheric
pressure by application of strong electric field to it. The charged liquid droplets
produced are then transmitted into the vacuum chamber of mass spectrometer which
vaporizes the solvent. The droplet size decreases and eventually charged analyte
(free of solvent) remains. Theory based research on ESI-MS has led to the development of nano electrospray, in which the electrostatic force establishes flow fate and
is thus independent of the solvent delivery (Wilm and Mann 1996).
The electrospray process results in multiple-protonation of proteins and peptides, and finds extensive application for accurate molecular weight determination
of thermally unstable, high molecular mass macromolecules such as proteins, oligonucleotides, and synthetic polymers (Ho et al. 2003). It has been significantly used
for mass determination of milk proteins, detection of modifications in proteins
caused by insertion, deletion or modification of amino acids, identification of
genetic variants and post-translational modifications like deamidation, oxidation,
glycosylation, phos- post-translational modifications, genetic polymorphorylation,
sulfation (Alomirah et al. 2000)
Since, ESI requires constant delivery of liquids; it can be easily coupled online
with liquid based separation systems such as HPLC chromatography for accurate
mass determination of proteins. It has been shown that liquid chromatography techniques coupled with tandem mass spectrometry (MS–MS) enhanced the capacity of
electrospray ionization to elucidate the structure of protein by sequence assignment
from peptide mapping (Leonil et al. 2000).
Other advances in the field of MS analysis of biomolecules include the use of
collision-cell CID of proteins in ESI-MS–MS experiments for elucidation purposes.
Liquid chromatography–tandem mass spectrometry with ESI ionization was successfully applied for the separation and identification of low molecular-mass peptides released during milk sterilization (Careri et al. 2002)
Matrix-Assisted Laser Desorption Mass Spectrometry (MALD-MS)
Though a very old technique introduced in 1988 by Karas and Hillenkamp, this
laser desorption mass spectrometry technique is an important tool for complex protein analysis which is valuable even in the present era. The procedure involves mixing of the sample with excess of matrix material usually organic acid of low
molecular mass in solvent. The matrix/analyte mixture is irradiated by a laser such
as nitrogen laser of wavelength 337 nm, nowadays, by UV laser which causes
desorption and ionisation of both matrix and analyte and their subsequent ejection
to vapour phase (Leonil et al. 2000). The analyte ions are finally measured on mass
spectrometer. MALDI-MS has proven useful for peptide mapping/MS and there are
several advantages in using these techniques. One crucial step of MALDI-MS is the
M. Manzoor et al.
Electro-Spray Ionization Mass Spectrometry (ESI-MS)
This is a “soft ionisation“technique that enables the analysis of large intact (underivatised) biomolecules, such as proteins and DNA. It involves atomisation of
solvent containing analyte into a spray of charged liquid droplets at an atmospheric
pressure by application of strong electric field to it. The charged liquid droplets
produced are then transmitted into the vacuum chamber of mass spectrometer which
vaporizes the solvent. The droplet size decreases and eventually charged analyte
(free of solvent) remains. Theory based research on ESI-MS has led to the development of nano electrospray, in which the electrostatic force establishes flow fate and
is thus independent of the solvent delivery (Wilm and Mann 1996).
The electrospray process results in multiple-protonation of proteins and peptides, and finds extensive application for accurate molecular weight determination
of thermally unstable, high molecular mass macromolecules such as proteins, oligonucleotides, and synthetic polymers (Ho et al. 2003). It has been significantly used
for mass determination of milk proteins, detection of modifications in proteins
caused by insertion, deletion or modification of amino acids, identification of
genetic variants and post-translational modifications like deamidation, oxidation,
glycosylation, phos- post-translational modifications, genetic polymorphorylation,
sulfation (Alomirah et al. 2000)
Since, ESI requires constant delivery of liquids; it can be easily coupled online
with liquid based separation systems such as HPLC chromatography for accurate
mass determination of proteins. It has been shown that liquid chromatography techniques coupled with tandem mass spectrometry (MS–MS) enhanced the capacity of
electrospray ionization to elucidate the structure of protein by sequence assignment
from peptide mapping (Leonil et al. 2000).
Other advances in the field of MS analysis of biomolecules include the use of
collision-cell CID of proteins in ESI-MS–MS experiments for elucidation purposes.
Liquid chromatography–tandem mass spectrometry with ESI ionization was successfully applied for the separation and identification of low molecular-mass peptides released during milk sterilization (Careri et al. 2002)
Matrix-Assisted Laser Desorption Mass Spectrometry (MALD-MS)
Though a very old technique introduced in 1988 by Karas and Hillenkamp, this
laser desorption mass spectrometry technique is an important tool for complex protein analysis which is valuable even in the present era. The procedure involves mixing of the sample with excess of matrix material usually organic acid of low
molecular mass in solvent. The matrix/analyte mixture is irradiated by a laser such
as nitrogen laser of wavelength 337 nm, nowadays, by UV laser which causes
desorption and ionisation of both matrix and analyte and their subsequent ejection
to vapour phase (Leonil et al. 2000). The analyte ions are finally measured on mass
spectrometer. MALDI-MS has proven useful for peptide mapping/MS and there are
several advantages in using these techniques. One crucial step of MALDI-MS is the
M. Manzoor et al.