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