Maldi Tof - Purvi Gosrani
Jun 14, 2015
Maldi Tof
- Purvi Gosrani
IntroductionMatrix-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 methods.
Method where a laser is used to generate ions of high molecular weight
samples, such as proteins and polymers
MechanismIt may involve absorption of light by the matrix
Transfer of this energy to the analyte-
which then ionizes into the gas phase as a result of the relatively large amount of energy absorbed
to accelerate the resulting ions into a flight-tube in the mass spectrometer they are subjected to a high electrical field
Parts of Maldi tof
1. Sample plate
2. Matrix
3. Laser
4. Variable voltage grid
5. Vaccum system
6. Flight tube
7. Time mass detectors
MatrixThe analyte incorporation in to a
suitable matrix is the first step of the
MALDI process, and is an important
feature of the MALDI method
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 :
Be able to embed and isolate analyte (e.g. by co-
crystallization)
Be soluble in solvents compatible with analyte
Be vacuum stable
Absorb the laser wavelength
Cause co-desorption of the analyte upon laser
irradiation
Promote analyte ionization
LaserNumerous 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.Neodymium-yttrium aluminum garnet (Nd:YAG)
Emits at 355 nm and gives a longer pulse time
IR lasers are also usedThe 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 biomolecules.
The MALDI method uses a pulse
laser
Laser fires in intervals
Pulsed laser produces individual
group of ions
1st pulse=1st group of ions
2nd pulse= 2nd group of ions, etc.
Each group of ions generated are
detected
With continuous pulsing, the signal
resolution increases
Time Mass Detector
The typical detector used with MALDI is the time of flight mass detector (TOF-MS)
• 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 energy.
• The time it takes for each ion to traverse
the flight tube and arrive at the detector is
based on its mass-to-charge ratio;
therefore the heavier ions have shorter
arrival times compared to lighter ions.
Advantages of Maldi Tof MS
•Soft ionization - analyze intact biomolecules and synthetic polymers
• Broad mass range - analyze a wide variety of biomolecules
• Simple mixtures are okay
• Relatively tolerant of buffers and salts
• Fast data acquisition
• Easy to use and maintain, no water or gas hook ups required
• High sensitivity, superior mass resolution and accuracy