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Method
detection limit of 5 ng per sample for each target PAHs
was achieved. Uncertainties of method precision with
each PAHs compound were evaluated through the determination
of replicate precision by comparing the same compound
result in replicate injections. The replicate precision
is calculated as a fraction of difference over averaged
values of the replicates. Determining the uncertainty
of the collected data was done by multiplying it with
the average replicate precision. The uncertainty value
is calculated by the root-mean-square of the above plus
the analytical detection limit, where:
This
effectively adjusts the uncertainty so that it equals
the detection limit when the sample data is zero, and
when the sample data is high, the detection limit will
become insignificant in the calculation.
The
uncertainty in the flow values (generally taken as 5%)
has also been root-mean-squared into the uncertainty
value when the units are converted from ng per sample
to ngm-3. Ten field samples were used for the evaluation
of method precision including sampling and analysis
performance. Table 5.3a presents the uncertainty values
for each target PAHs and the percentage difference relative
to the mean value
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0.54
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