Selected Reaction Monitoring; Autosim; Data Types - Thermo Scientific TSQ Series Hardware Manual

Selected Reaction Monitoring

AutoSIM

Data Types

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SIM can improve the detection limit and decrease analysis time, but it can also reduce
specificity. Because SIM monitors only specific ions, any compound that fragments to
produce those ions will appear to be the target compound. The result can be a false positive.
Selected reaction monitoring (SRM) monitors a particular reaction or set of reactions, such as
the fragmentation of an ion or the loss of a neutral moiety.
SRM monitors a limited number of parent or product ion pairs. In product-type experiments,
a parent ion is selected as usual, but generally only one product ion is monitored. SRM
experiments are normally conducted with the product scan mode.
As does SIM, SRM provides for the very rapid analysis of trace components in complex
mixtures. However, because SRM selects two sets of ions, it obtains specificity that is much
greater than what SIM can obtain. Any interfering compound would not only have to form
an ion source product (parent ion) of the same mass-to-charge ratio as the selected parent ion
from the target compound, but that parent ion would also have to fragment to form a product
ion of the same mass-to-charge ratio as the selected product ion from the target compound.
In the scan type known as AutoSIM, the mass spectrometer automatically selects the most
intense masses (m/z values) in a survey scan, builds a SIM scan list for them, and then acquires
and records ion current at only these selected masses. AutoSIM scans can be performed on any
full scan in any scan mode but not on data-dependent scans.
There might be times when the scan ranges of two (or more) selected masses overlap. If this
happens, both masses are placed in one SIM window. In EZ Tune, the SIM table in the
Define Scan dialog box displays the center mass for this new scan window, not each selected
mass.
You can acquire and display mass spectral data (intensity versus mass-to-charge ratio) with the
TSQ mass spectrometer in one of two data types:
• Profile Data Type
• Centroid Data Type
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Introduction
Data Types
TSQ Series Hardware Manual 11