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Detection limit
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The detection limit, LD, answers the question:

"If you were to measure a sample, what would the count rate have to be for, say, 95% certainty of detection?"

A distribution of counts, were we to measure the sample a large number of times, would have a standard deviation of sD. We need to be certain, to a degree determined by kb, that the chance of not detecting the activity when it is really there is only b, i.e.

LD = LC + kbsD = kas0 + kbsD 

When ka and kb correspond to the 95% confidence level

\ LD = 2.71 + 4.65s

where s is the standard deviation of the background counts.

If the calculated peak area is less than LC then we must quote a limit of measurement. Otherwise we can quote the estimate uncertainty.



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1999, 2000 The University of Liverpool, Department of Physics

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