Mass Spectrometry

lc-ms mc-ms

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Mass spectrometry

Mass spectrometry is an analytical technique used for measuring the molecular mass of a sample. 

we have different masses for the same compound due to ISOTOPES.

Mass spectrometry (MS) is used to determine:

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The instrument

Ionisation and fragmentation of molecules by a variety of means with the use ofFour Separation process. (CE, LC, GC, ICP).

                                    Ionisation methods in GC-MS                                                  (http://i52.tinypic.com/jhai6q.jpg)


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         Ionisation methods in GC-MS (cont-d) 

            Chemical Ionisation (CI)    

  •  CI uses a reagent ion to react with the analyte molecules to form ions by either a proton or hydride transfer.
  • The reagent ions are produced by introducing a large excess ofa reagent gas (relative to the analyte), e.g. methane, ammoniaor isobutane, into an electron impact (EI) ion source
  • For methane, electron collisions produce CH4 + and CH3 + which react with further methane molecules to form CH5+ and C2H5
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                                 Ionisation methods in LC-MS

(http://i53.tinypic.com/2mnktu0.jpg)

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Selection of masses in the analyzer using different approaches:

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(http://i53.tinypic.com/2sbacl5.jpg)


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Tandem mass spectrometry

Tandem mass spectrometry (MS-MS) is used to produce structural information about a compound by fragmenting specific sample ions through a secondary fragmentation process inside the mass spectrometer and identifying the resulting fragment ions (daughter ions)

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The Tandem mass spectrometry  is a mass spectrometer that has more than one analyser. The analysers are separated by a collision cell into which an inert gas (e.g. argon, xenon) is admitted to collide with the selected sample ions and bring about their fragmentation.

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Advantages of using MS

Advantages of using MS:


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Forensic Application

Forensic Application of LC-MS and GCMS.

LC-MS is used for the identification of dyes extracted from textile fibers and the utility of the method for forensic trace analysis is demonstrated. The technique is shown to provide a high degree of chemical structural information,making dye identification highly specific in comparison to optical and/or chromatographic methods of dye analysis.

GC-MS-MS method for determining trace concentrations of gammahydroxybutyrate (GHB) in blood and urine has been developed. Multiplereaction monitoring was used to detect parent and daughter ions of GHB,233 and 147.

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