Glossary of Terms 324
V4.2 LabChip GX User Manual PerkinElmer
Slope Threshold
The Slope Threshold setting represents the amount of change in
response over time required to differentiate between a peak and
baseline noise. Changing this setting may cause certain peaks that
were previously detected to be ignored or to interpret noise as
peaks. For details, see “Understanding Peak Finding” on page 108.
The Slope Threshold setting can be changed in the Peak Find Tab.
Smear
Specifies a size range in which to detect the region of the
fluorescence signal instead of specifying a specific size for a peak.
Use a smear to detect a broad mix of molecules of similar but
distinct sizes in a sample. The concentration or fractional presence
within a specified range of molecule sizes is measured. Specify the
Start Size and End Size of a smear in the Assay Analysis Window
on the Smear Analysis Tab.
The Smear Properties can be viewed in table form in the Well Table
View. To view the Smear Properties in the table, add the desired
property to the Well Table View. The properties extracted from the
smear match those of a peak, having start and end points, area,
concentration, etc. % Purity is the ratio of smear concentration to
total sample peak concentration, exclusive of markers, system
peaks, and excluded peaks. Excluded peaks are not excluded from
analysis calculations such as concentration or area within the
smear region, so the limits must avoid excluded peaks. An
additional Peak Count property is available for smears. Peak Count
is the number of non-excluded sample peaks in the region, where
the center of the peak is inside the smear limits.
In the Graph View, the smear regions display with the start and end
points drawn at the base of the smear in the chosen color and the
trace highlighted with the smear color. Override the smear baseline
by dragging with the mouse in the Graph view. The baseline start
and end points can be adjusted in the graph to change the height of
the baseline or the size range of the smear. Smears can overlap to
include the same region in multiple smears.
In the Gel View, the smear region is shown on the gel as a colorized
region. The color is a transparent version of the color selected for
the region, so that the fluorescence intensity shows through.
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