Estimating Limit of Detection of analytical instruments?

As the title says, how could you ESTIMATE the limit of detection of HPLC and UV-Vis instruments, ONLY by looking at the signals of the lowest standard used and the blanks? (ie, only ONE standard and ONE blank can be used)

Thanks

P.S. Sorry about the caps lock, just want to make it clear that the question I need to answer asks for an estimate using the above method.