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Introduction
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____________________________________________________________________ Scan Types
_______________________ Finnigan LTQ Hardware Manual _____________________
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parent ions are excited so that they collide with background gas. The
collisions of the new parent ions cause them to fragment to produce one or
more new product ions.
In the third stage of mass analysis, the new product ions are stored in the mass
analyzer. The process described in the previous paragraph is repeated up to
seven more times until the final product ions of interest are produced.
In the nth stage of mass analysis, the final product ions are stored in the mass
analyzer. Ions of one or more mass-to-charge ratios are selected and all other
ions are ejected from the mass analyzer. Then, the selected ions are
sequentially scanned out of the mass analyzer to produce a CRM final product
ion mass spectrum.
In CRM, the specificity increases as the number of consecutive reactions that
you monitor increases. However, the sensitivity decreases as the number of
consecutive reactions that you monitor increases—especially if there are
many fragmentation pathways available to the ion.
ZoomScan
The determination of the mass of an ion from its mass-to-charge ratio may be
complicated by the fact that the charge state of the ion may be unknown.
ZoomScan is a high resolution MS scan type in which LTQ performs a high
resolution scan that allows you to determine the charge state and molecular
weight of an ion. LTQ conducts a high resolution scan of 10 u width and
evaluates the
12
C /
13
C isotopic separation of a specified ion or ions. If the
isotopic peaks are 1 u apart, the ion has a charge state of
±
1. If the isotopic
peaks are 0.5 u apart, the ion has a charge state of
±
2. If the isotopic peaks are
0.33 u apart, the ion has a charge state of
±
3, and so on. You can then
determine the molecular weight of the ion from a knowledge of the charge
state and mass-to-charge ratio of the ion. You can conduct a ZoomScan
analysis of up to ten ions by specifying the mass-to-charge ratios of the ions.