TAILIEUCHUNG - Ionization Methods in Organic Mass Spectrometry

If you would like to challenge your students and engage them more actively in the scientific process, you can use the second laboratory day for a student-designed investigation. Each group of students will develop their own plan to identify the thief by testing Jerell's evidence and the types of food that were eaten by the coworkers for the different types of organic compounds. For this investigation activity, you can use the last page of these Teacher Preparation Notes to replace pages 5-6 of the Student Handout. You may want to have a class discussion of the strengths and weaknesses of. | Ionization Methods in Organic Mass Spectrometry Contents Introduction Gas-Phase Ionization . Electron Ionization EI . Chemical Ionization CI . Desorption Chemical Ionization DCI . Negative-ion chemical ionization Field Desorption and Ionization . Field Desorption FD . Field Ionization FI Particle Bombardment . Fast Atom Bombardment FAB . Secondary Ion Mass Spectrometry SIMS Atmospheric Pressure Ionization . Electrospray Ionization ESI . Atmospheric Pressure Chemical Ionization APCI Laser Desorption . Matrix-Assisted Laser Desorption Ionization MALDI Appendices . CI Reagent Gases . Direct Formation of Negative Ions . FAB matrices Introduction A mass spectrometer works by using magnetic and electric fields to exert forces on charged particles ions in a vacuum. Therefore a compound must be charged or ionized to be analyzed by a mass spectrometer. Furthermore the ions must be introduced in the gas phase into the vacuum system of the mass spectrometer. This is easily done for gaseous or heat-volatile samples. However many thermally labile analytes decompose upon heating. These kinds of samples require either desorption or desolvation methods if they are to be analyzed by mass spectrometry. Although ionization and desorption desolvation are usually separate processes the term ionization method is commonly used to refer to both ionization and desorption or desolvation methods. The choice of ionization method depends on the nature of the sample and the type of information required from the analysis. So-called soft ionization methods such as field desorption and electrospray ionization tend to produce mass spectra with little or no fragment-ion content. Gas-Phase Ionization These methods rely upon ionizing gas-phase samples. The samples are usually introduced through a heated batch inlet heated direct insertion probe or a gas chromatograph. Electron Ionization EI Summary Also referred to as electron impact ionization this is the oldest and best-characterized of all the .

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