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How can I determine experimentally the quantitation limit of my method, i.e., the lowest amount that can be accuratly and precisely determined using the method I developed for my GC?

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Prepare standards at various levels and analyze each one in triplicate (or you can use more replicates). Calculate the %RSD of the 3 injections of each concentration of standard. If the % RSD for a certain concentration of standard goes above a certain amount (we use 3 %), you are at the quantitation limit. Actually the lowest level standard that is still below 3% RSD is what we consider to be the quantitation limit. This seems to work pretty well. Hope this helps.

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Conceptually, it might be easier to use the signal to noise ratio (S/N). S/N of 2-4 are usually considered to be the limit.

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We inject a blanco 6 times, calculate noise at the retention time of our peak, and 3.3 times the noise level = LOD, LOQ = 10 x noiselevel