4G Detection Limits
The focus of this chapter has been the evaluation of analytical data, including the
use of statistics. In this final section we consider how statistics may be used to characterize
a method’s ability to detect trace amounts of an analyte.
A method’s detection limit is the smallest amount or concentration of analyte
that can be detected with statistical confidence. The International Union of Pure
and Applied Chemistry (IUPAC) defines the detection limit as the smallest concentration
or absolute amount of analyte that has a signal significantly larger than the
signal arising from a reagent blank. Mathematically, the analyte’s signal at the detection
limit, (SA)DL, is
(SA)DL = Sreag + zσreag 4.25
where Sreag is the signal for a reagent blank, σreag is the known standard deviation
for the reagent blank’s signal, and z is a factor accounting for the desired
confidence level. The concentration, (CA)DL, or absolute amount of analyte,
(nA)DL, at the detection limit can be determined from the signal at the detection limit.
