how are detection limits related to standard deviations and why does this relationship exist?

Question

how are detection limits related to standard deviations and why does this relationship exist?

Answer 1

All instruments have some inherent noise. If you measure a sample, even if it's a blank, there is going to be some noise from the instrument. If you measure a blank sample three times you can get the average of the noise and then the standard deviation of the noise. If you take the signal of the blank and add three times the standard deviation of the noise to it, this gives you a 95% confidence interval that you have a signal that is different from the noise of your instrument.