Spectradyne nCS1, Operation Manual, Page: 33 / 40

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33
Version 2.5.0 Revision 3, July 2020
Identifying False Positives Among the Measured Peaks
False positives generally are characterized as follows (example shown in Figure 18):
➢
Diameter:
o
Diameter near or below the small size limit of detection of the cartridge.
➢
Transit time:
o
A group of small diameter particle events having a broad distribution of transit
times.
➢
Symmetry:
o
Symmetry outside the range of 0.2 – 4.0 (approx.)
➢
Signal-to-noise (S/N):
o
S/N < 15 (cartridge dependent).
o
A general sense for an appropriate S/N cutoff can also be obtained by inspecting
peaks in the raw data (Figure 17 and
“ Viewing the Results of Raw Data
Processing ,” page 26).
Figure 18. Representative Scatter plot of Diameter vs. Transit Time showing two distinct
populations of true particle detection events (red) and false positives excluded from the data set
(blue).
False positive detection events are characterized in part by having diameter close to the
minimum detectable size for the cartridge (here approx. 130 nm) and a broad distribution of transit
times.