Glossary of Terms 174
P/N CLS151164 Rev. B LabChip GX Touch/GXII Touch User Manual PerkinElmer, Inc.
Peak Baseline
A local peak baseline is calculated for each peak. For isolated
peaks, the local peak baseline is a straight line connecting the start
point with the end point. For peaks that are very close together, an
average baseline is used when the value between the peaks does
not drop to the actual baseline. The peak baseline for two peaks is
shown in Figure 64.
Figure 64. Peak Baselines
The peak baseline algorithm starts at the earliest peak and checks
whether the end point is within a certain distance from the start of
the next peak. When a cluster of peaks is detected, the peak
baseline is the line joining the first peak's start to the last peak's
end. The start and end points of adjacent peaks in the cluster are
averaged to the same point so that no gaps exist between peaks.
Peak Identification
From the smoothed data, peaks are identified using a hill-climbing
algorithm running along the smoothed data and its first derivative.
The peak baseline is drawn across the peak bottom by taking local
averages just outside the peak start and end points and connecting
the two points. The peak height, measured from the apex down to
the peak baseline, must exceed the minimum peak height specified
in the analysis settings for the bump to be identified as a peak.
Analysis settings can only be changed when reviewing LabChip GX
Touch data in the LabChip GX Reviewer software.
The peak start, end, and baseline can be viewed in the EGram Tab
by selecting the Show Peak Baselines option in the Graph
Settings. The area of each peak is determined by trapezoidal
integration of the peak signal between peak boundaries and above
the peak baseline.
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