What is electron impact mass spectrometry?
In electron impact mass spectrometry, the collision of a high energy electron with a sample molecule produces a radical cation, M+·. The first ion that forms in this process is the parent ion.
Why is electron impact typically used on gas chromatography instruments?
Electron Impact and Chemical Ionization EI and CI are gas-phase techniques that are readily interfaced with a gas chromatograph (GC) enabling complex mixtures to be efficiently separated by GC with subsequent component identification by MS. EI imparts high energy to the sample resulting in extensive fragmentation.
What is electron ionization in mass spectrometry?
Electron ionization (EI, formerly known as electron impact ionization and electron bombardment ionization) is an ionization method in which energetic electrons interact with solid or gas phase atoms or molecules to produce ions. EI was one of the first ionization techniques developed for mass spectrometry.
How is electron impact done?
Electron impact (also known as electron ionisation) The high energy electrons come from an ‘electron gun’ which is a hot wire filament with a current running through it that emits electrons. This usually knocks off one electron from each particle forming a 1+ ion.
How do the spectra for the electron impact and the chemical ionization sources differ from one another?
How do the spectra differ for EI, field ionization, and CI sources differ from one another? The most fragementation and thus the most complex spectra are encountered with electron impact ionization. Field ionization produces the simplest spectra.
How do the spectra obtained with electron impact ionization differ from the spectra from chemical ionization?
Chemical ionization delivers less energy to the analytes and as a result causes less molecular fragmentation. Compared to EI, this technique provides less energy resulting in “soft” ionization. Mass spectra acquired from a CI source generally contain the molecular ion.
Why is a negatively charged plate used in mass spectrometry?
This usually knocks off one electron from each particle forming a 1+ ion. The 1+ ions are then attracted towards a negative electric plate where they are accelerated. This technique is used for elements and substances with low formula mass (that can be inorganic or organic molecules).
What are the source parameters for electron impact?
Electron Impact Source Parameters Source temperature, emission current, electron voltage
What is electron ionization used for in MS?
Electron ionization (EI), originally developed by Dempster,28 is widely used in MS for relatively volatile samples that are thermally stable and have relatively low molecular weight. Samples are typically presented in the effluent from a GC or are volatilized from a solids probe inserted into the high vacuum source.
What is the difference between GC and mass spectrometry?
(SCD). Another common GC detector is the mass spectrometer. Mass spectrometry (MS) is a technique that is used to elucidate molecular mass and molecular structure for compound identification and/or quantification. While MS can be done without GC separation, interpretation of the data becomes increasingly more difficult when analyzing mixtures.
What is direct insertion electron ionization mass spectrometry (EI-MS)?
Direct insertion electron ionization mass spectrometry (direct insertion EI-MS) has been used for the identification of archaeological adhesives such as tars, resins and waxes found during excavations on archaeological sites.