Matrix-assisted laser desorption/ionization (MALDI) is a soft
ionization technique used in mass spectroscopy, allowing the
analysis of biomolecules (biopolymers such as DNA, Proteins,
peptide and sugars) and organic molecules (such as polymers,
dendrimers and other macromolecules), which tend to be fragile
and fragment when ionized by more conventional ionization
Method where a laser is used to generate ions of high molecular
weight samples, such as proteins and polymers.
It may involve absorption of
light by the matrix.
Transfer of this energy to the
analyteo which then ionizes into the
gas phase as a result of the
relatively large amount of
o To accelerate the resulting
ions into a flight-tube in the
mass spectrometer they are
subjected to a high electrical
The MALDI technique combined with a MS detector
(MALDI-MS) became an indispensable tool in analysis of
biomolecules and organic macromolecules.
MALDI involves incorporation of the analyte into a matrix,
absorption/desorption of laser radiation, and then ionization of
The analyte incorporation in to a suitable matrix is the first
step of the MALDI process, and is an important feature of the
A typical sample preparation involves using 10-6 M solution of
the analyte mixed with 0.1 M solution of the matrix.
The solvents are then evaporated in a vacuum of the MS, and
the matrix crystallizes with the analyte incorporated.
According to Sigma Aldrich, the matrix must meet the
following properties and requirements :
o Be able to embed and isolate analyte (e.g. by cocrystallization)
o Be soluble in solvents compatible with analyte
o Be vacuum stable
o Absorb the laser wavelength
o Cause co-desorption of the analyte upon laser irradiation
o Promote analyte ionization
gas and solid state lasers have been developed for
use in MALDI.
Most MALDI devices use a pulsed UV laser
N2 source at 337 nm.
aluminum garnet (Nd:YAG)
Emits at 355 nm and gives a longer pulse time
IR lasers are also used
The most common IR laser is the erbium doped-yttrium
aluminum garnet (Er:YAG).
Emits at 2.94 micrometer.
It is “softer” than the UV, which is useful for certain
The typical detector used with
MALDI is the time of flight mass
o TOF is a method where the ions
are accelerated by an electric field,
resulting in ions of the same
strength to have the same kinetic
o The time it takes for each ion to
traverse the flight tube and arrive
at the detector is based on its massto-charge ratio; therefore the
heavier ions have shorter arrival
times compared to lighter ions.
Applications of MALDI mass spectrometry in detection ofo Synthetic polymers
o Peptides and proteins
o Bacterial identification
MALDI-MS is a vital tool in mass analysis of biomolecules
and organic macromolecules.
Detection limits of femtomole to attomole.
Reproducibility is relative.
Complimentary technique to ESI (electrospray ionization)