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Measurement and Results - Uncertainty associated with limit of quantitation (LOQ)

 
I was reading your online guide http://www.inorganicventures.com/linearity-and-detection-limits and wanted to clarify your statement regarding the Limit of Quantitation.You said "Limit of Quantitation (LOQ) is defined as 10*SD (10x standard deviation) and will have an uncertainty of ~ 30% at the 95% confidence level." Does the uncertainty refer to the uncertainty of measurement at the LOQ, or is it how uncertain you are that the LOQ is accurate?
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The statement refers to the uncertainly in the LOQ. For example, if the LOQ is calculated as 100 ppt (parts-per-trillion), then the LOQ could be stated as “LOQ = 100 ppt +/- 30 ppt (with a 95% confidence interval). The concern when measuring near a LOQ is that it’s not possible to know if you are quantifying the analyte concentration, or simply measuring the noise around the LOQ. In the example above of a LOQ = 100 ppt +/- 30 ppt, it may be more appropriate to define the LOQ as being equal to 130 ppt, as there is only a small chance that a result greater than 130 ppt is not a real measurement of the analyte concentration.
Posted: 09/05/18 22:29:58

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