134 Understanding Your Agilent ChemStation
6 Peak Identification
Corrected Retention/Migration Times
Corrected Retention/Migration Times
To match peaks by absolute retention/migration times may be simple but not
always reliable. Individual retention/migration times may vary slightly due to
a small change in conditions or technique. As a result peaks may occur outside
the peak matching windows and therefore are not identified.
A technique to deal with the inevitable fluctuations that occur in absolute
retention/migration times is to express component retention/migration times
relative to one or more reference peaks.
Reference peaks are identified in the calibration table with an entry in the
reference column for that peak. The relative peak matching technique uses the
reference peak or peaks to modify the location of the peak matching windows
in order to compensate for shifts in the retention/migration times of sample
peaks.
If no reference peak is defined in the method or the ChemStation cannot
identify at least one reference peak during the run, the software will use
absolute retention/migration times for identification.
Single Reference Peaks
A retention/migration time window for the reference peak is created around
its retention/migration time. The largest peak falling within this window is
identified as the reference peak. The expected retention/migration times of all
other peaks in the calibration table are corrected, in proportion to the ratio of
the expected retention/migration time to the actual retention/migration time
of the reference peak.
Multiple Reference Peaks
Correcting retention/migration times with a single reference peak is based on
the assumption that the deviation of actual retention/migration time from the
expected retention/migration times changes uniformly and linearly as the run
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