"Isotopes"
"an IonSource.Com tutorial"

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.Tutorial Glossary 

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Term

Definition

mmu

Millimass Unit, 0.001  amu

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amu

Atomic Mass Unit, some would argue that (mu) is a more appropriate term.  We choose to use amu in this tutorial.
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Mu is defined as 1/12 the set mass of carbon.  
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isotope Elements are made up of naturally occurring isotopes.   These isotopes have the same chemical characteristics but differ by mass.  Each isotope has the same number of protons but differ in the number of neutrons. 
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monoisotope
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average mass
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atomic mass
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monoisotopic mass
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nitrogen rule
"crossover mass" My own term, used to describe the mass where the A+1 isotope begins to compete for base peak status with the "A" ion.  This mass is slightly different for compounds with different elemental compositions and can be wildly different for those compounds with weird A+2 type elements.   
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A, A+1, A+2 peaks
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FAB Fast Atom Bombardment. Technique used to ionize a compound usually in a glycerol matrix by bombarding it with xenon atoms or other neutral atoms.  The ionization is accomplished in a vacuum with the sample placed on a probe, although flow FAB at low flow rates is sometimes practiced.  Most often used in conjunction with a high resolution magnetic sector mass spectrometer.  A very good description of FAB can be found at 
base peak  Tallest or most abundant peak in the mass spectrum.

.(slide jumper) Index Glossary Comp. 1 2 3 4 5 6 7 8

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Last updated: Tuesday June 27th, 2000 11:34:58 PM