Interpretation of this sentence

[tlili]

Dear guys,

I am trying to figure out what the following sentence means:

"The limit of detection (LOD) was defined as the sample concentration resulting in a peak area of 3 times the noise level" . In this case, how much is the LOD? Appreciate if someone can help to explain this (if possible with some figures so as I can have a better idea).

This was extracted from J Chromatogr: rapid and simple determination of doxcycline in serum by HPLC pg 297.

[TOT]

Hi,
This sentence can be explained like following:
- Determine the noise of baseline from your chromatograph.
- Multiple this number with 3.
- Put this number in your calibration curve equation (y=mx+b) in the position of y, from that you calculate the value of x, this is limit of detection.
If you want to know th way to determine the noise, you can refer to USP, they have very clear demonstration there!
Hope that this explaination could hepl!

[tlili]

Thanks, Tot. Still not very sure.

You mention about USP. What does it represent? How do I go about to refer? Thanks for all the info.

[TOT]

Hi tlili,
USP= United States Pharmacopoeia.
Another way to interpret your sentence is: Prepare a range of solutions with different concentration. Record the solution which gives the response 3 times higher than the noise. The concetration of this colution is limit of detection.
Hope this time is clearer for you!