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:
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
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
Ionisation methods in LC-MS
Selection of masses in the analyzer using different approaches:
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)
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.
Advantages of using MS
Advantages of using MS:
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.