Mass Spectrometry Handout

Mass Spectrometry Handout - Mass Spectrometry Handout Mass...

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Mass Spectrometry Handout Mass spectrometry is used for determining the molecular weight of a compound and possibly identifying components of a compound. Mass spectrums identify a cation radical or cation. If the particle of interest is not positively charged, it will not be seen. An example of a mass spectrum is given below. There are a couple of terms that you should with which you should become familiar. Mass spectrum of toluene. Courtesy of the Integrated Spectral Data Base System for Organic Compounds by the Japanese National Institute of Advanced Industrial Science and Technology. http://www.aist.go.jp/RIODB/SDBS/menu-e.html Many spectra will be used from this resource. Terms M/Z: mass to charge ratio. For our purposes, the charge will be assumed to be one so that the value of m/z corresponds to the mass. Mass ion peak: M+ is the molecular ion for the molecule. For toluene which has a molecular weight of 92, it is the peak at 92. For most molecules the M+ peak is seen on the mass spectrum but it is not seen if formation of a stable cation is possible. (i.e. tertiary alcohols) M+1 peak: This peak is one mass unit greater than the mass ion peak. For toluene, this peak is seen at 93. M+2 peak: This peak is two mass units greater than the mass ion peak. For toluene, this peak is barely seen at 94.
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Base peak: This peak is the peak with the relative intensity of 100 %. The base peak is caused by the most stable cation. For toluene, the base peak is at 91. Resolution: Resolution is measured from peak heights and spacing. The two resolutions are low resolution and high resolution. Low resolution is to whole numbers (i.e. 44) while high resolution is to more numbers (i.e. 44.04356) Possible methods to make the cation for MS EI: Electron ionization with a stream of high energy electrons (70 electron volts). All of
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This note was uploaded on 03/24/2009 for the course CHEMISTRY 030.225 taught by Professor Janegreco during the Spring '09 term at Johns Hopkins.

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Mass Spectrometry Handout - Mass Spectrometry Handout Mass...

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