Group

M.Asif Javaid

M. Saim Riaz

Nabia Fatima

TENDOM MASS SPECTROMETRY

MULTIPLE TYPE MASS SPECTROMETRIC METHOD

Tandem MS:M

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PRINCIPAL It can be performed by first selecting and isolating a precursor ion MS2,fragmenting it,isolating a primary fragment ion MS3,fragmentig it ,isolating a secondary fragment MS4,and so on as long you can obtain meaningful information or the fragment ion signal is detectable.

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Tandem MS Instruments:

TANDEM IN SPACE

TANDEM IN TIME

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Tandem in space:

The separation elements are physically separated and distinct.

There is a physical connection between the elements

to maintain high vacuum.

These elements can be sectors, transmission quadrupole, or time-of-flight.

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Tandem in time:

The separation is accomplished with ions trapped in the same place, with multiple separation steps taking place over time.

A quadrupole ion trap or FTMS instrument can be used for such an analysis.

Trapping instruments can perform multiple steps of analysis, which is sometimes referred to as MSn (MS to the n).

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Notation:

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Tandem mass spectrometry:There are four main scan experiments possible using MS/MS:

Precursor ion scan

A precursor ion scan cannot be done with time based MS instruments.

Note that precursor ion is synonymous with parent ion .

product ion with daughter ion however the use of these anthropomorphic terms is discouraged.

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Product ion scan

A precursor ion is selected in the first stage, allowed to fragment .

Then all resultant masses are scanned in the second mass analyzer and detected in the detector that is positioned after the second mass analyzer.

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Selected reaction monitoring

Both mass analyzers are set to a selected mass.

This mode is analogous to selected ion monitoring for MS experiments.

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Neutral loss scan The first mass analyzer scans all the masses. The second mass analyzer also scans, but at a

set offset from the first mass analyzer.  This offset corresponds to a neutral loss that is

commonly observed for the class of compounds. Neutral loss scans cannot be done with time

based MS instruments. In a constant-neutral-loss scan, all precursors

that undergo the loss of a specified common neutral are monitored.

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Fragmentation in tandem mass spectrometry

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In-source fragmentation:

If the product ions persist in their non-equilibrium state for a moderate amount of time before auto-dissociation this process is called metastable fragmentation

Nozzle-skimmer fragmentation refers to the purposeful induction of in-source fragmentation by increasing the nozzle-skimmer potential on usually electrospray based instruments.

It is not technically tandem mass spectrometry unless metastable ions are mass analyzed or selected before auto-dissociation and a second stage of analysis is performed on the resulting fragment.

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Post-source fragmentation Energy can also be added to the ions, which are usually

already vibrationally excited, through post-source collisions with neutral atoms or molecules, the absorption of radiation, or the transfer or capture of an electron by a multiply charged ion.

 Collision-induced dissociation(CID), also called collisionally activated dissociation(CAD), involves the collision of an ion with a neutral atom or molecule in the gas phase and subsequent dissociation of the ion.

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Post Source Fragmentation

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 A peptide sequence tag obtained by tandem mass spectrometry can be used to identify a peptide in a protein database.

.A notation has been developed for indicating peptide fragments that arise from a tandem mass spectrum

. Peptide fragment ions are indicated by a, b, or c if the charge is retained on the N-terminus and by x, yor z if the charge is maintained on the C-terminus.The subscript indicates the number of amino acid residues fragment

Peptide fragmentation:

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