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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: ubcdumbass on February 09, 2019, 05:04:28 PM

(3)An assay method has a simple linear calibration: S = 0.50[A] –2.00, where S is the measured signal(arbitrary units)and [A] is the concentration of analyte in units of micromolar. A blank sample is measured five times and an average signal of 0.50 ±0.50(± one standard deviation) is obtained. What is the limit of detection for the method?
The answer is 8.0 uM. Unsure why as LOD= Smb + zo, wherein the textbook it says z is assumed to be 3 when no other assumptions can be made. (is this true?)
That would give 2.0uM
Could somebody run me through this? Thank you

Your formula would give 2.0 signal units. Put this into your calibration equation, and you get [A] = 8.0 µM.