Chapter 5: Limit of Detection and Limit of Quantitation | CHM 214 | 040

[@ThePigeonBrain]

For those wondering what to do when you can't measure blanks (for example, a gcms returns no value if there's no peak), it's a bit more finicky. You make some measurements to figure out what the lowest you can go is, then measure that sample, say, 10 times. Convert to concentration, and find the average concentration x. Then, LOD=x+5*standard deviation.

[@배연욱-q7t]

Thanks for your effort!

[@chaerunraudhatulislam5990]

Thank you so much! Great video!

[@afuwakagoya1356]

Thank you so much. This is really helpful. My question is; which slope do we use? Do we use the slope for the blanks or for the calibration curves of the standards

[@jacobstewartchem]

You will use the slope of the calibration curve of the standards. Glad that you found the video helpful!

[@loyalperformance3139]

Thank you so much !!! this video really helped me very much

[@paulinabelvoncikova1921]

Hi, I am struggling to understand, what should I do if my slope is negative? Can I use absolute value of it? Thank You

[@regardalestair8728]

use the negative value..

[@ralarcon337]

Thanks! This is super useful :)

[@jacobstewartchem]

Glad I could help.

[@zbfa9224]

Hi Jacob, your explanation is very straightforward! I was wondering should I interpret the SD of the signal from a blank as the "SD of the intercept" of the linear regression formula?

[@jacobstewartchem]

Hello, glad the video was helpful. To answer your question, no those are two different things. You would get the SD of the signal from a blank by measuring the signal from a blank sample multiple times and calculating the standard deviation of those values. Doing this measurement gives and idea of how much your signal varies just from the instrument or technique you are using. This is different than the SD of the intercept that you'll get from a linear regression formula.