Non-Fitted Calculations
Lynx II DSA User's Manual – 7096089 193
FWHM and FWTM
The Full Width at Half Maximum (FWHM) and Full Width at Tenth Maximum (FWTM)
algorithms calculate the current peak width at one-half (one-tenth) of its maximum
amplitude.
The current ROI determines the search limits and the background. The highest channel
within this ROI, corrected for the sloped background, is located using 3-point smoothed
data.
The Half Maximum value equals the counts in the highest channel (determined by a 3-
point smooth) background corrected and divided by 2.
The Tenth Maximum value equals the counts in the highest channel (determined by a 3-
point smooth) background corrected and divided by 10. The background is a straight line
connecting the four-channel averaged endpoints of the ROI.
Using data in the highest channel, proceed down each side of the peak to locate the
channel whose background-corrected counts fall below the designated Half Maximum
(Tenth Maximum) value.
The left and right FWHM (FWTM) points are the interpolated channels between the
counts of the channel below the Half Maximum (Tenth Maximum) value and the counts of
the channel above the Half Maximum (Tenth Maximum) value.
Smoothing the data of the wider peaks can improve the performance of the FWHM,
FWTM, and Centroid calculations, but results may be misleading or insignificant if data is
smoothed on narrow peaks. Therefore, raw (unsmoothed) data is used for peaks of 20
channels or less.
Area
The net peak area for a single peak is calculated as follows
(2) S = G – B
where
S is the net peak area,
G is the sum of gross counts in the peak ROI, and
B is the continuum.
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