Mass spectrometer: Difference between revisions

Revision as of 18:52, 26 January 2004

Revision as of 10:21, 3 February 2004

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The most common form of mass spectroscopy is gas chromatography-mass spectroscopy (GC/MS). In this technique a [[gas chromatograph]] is used to separate compounds. This stream is fed into the ion source, a metallic filament to which voltage is applied. This filament discharges electrons which ionizes compounds. The ions can then further fragment, yeilding predictable patterns. The stream then passes into the detector.

For large molecules typical of biological applications, special techniques are used. The ion source subjects a sample of material to an [[Electric charge|electrical charge]] that causes the material to be ionized. The ions are then transported by magnetic or electrical fields to the mass analyzer. Types of ion sources include [[electrospray ionization]], chemical ionization, fast atom bombardment, and [[matrix-assisted laser desorption ionization]], [[Thermal Ionisation (TIMS)]] , [[Secondary Ionisation (SIMS)]] and [[Plasmas Source]].

Atmospheric Pressure chemical Ionization (APcI), an adaption of chemical ionization allows for high flow rates typical of [[HPLC]] to be used directly, often without diverting the larger fraction of volume to waste. Typically these mobile phase / analyte sytems are heated to temperatures in excess of 400 degrees Celsius, sprayed with high flow rates of nitrogen and the entire aerosol cloud is subjected to a corona discharge that creates ions. The term "chemical" ionization comes from the fact that the initial ions produced are typically those of the mobile phase and its modifiers. The analyte is ionized by charge transfer during collisions in the high (atmospheric) pressure region of the outer source.