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Liquid Liquid Extraction Acceptable Recovery STD DEV

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

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Hello all,

I have recently performed a Liquid Liquid Extraction with good recovery. To determine the recovery I used the average recovery values from three replicate extractions at the same concentrations. I then took the standard deviation of these 3, and I found my numbers to be around 75% Absolute recovery +/- ~10-15 as the standard deviation.

My question is simple. I am quite happy with my analytical recovery. The only question is about the standard deviation for recovery of the replicate extracts.

What is the acceptable standard deviation limits for recovery? Also, are there any guidelines from the FDA or any other resources analytical resource?

-Many Thanks!
I'm not sure about FDA guidances on precision, but some EPA method specify that. EPA methods typically require an Initial Demostration of Capability - 7 analyses spiked with analytes. Requirements vary by method, but two liquid-liquid extractions I know of are 551.1 <15% RSD and 552.2 <20% RSD.

EPA methods are available online at http://www.nemi.gov
Also, are there any guidelines from the FDA or any other resources analytical resource?
There are lots of guidelines out there. The answer to your question depends not so much on the technique being used (LLE) so much as the purpose of the analysis (15% RSD might be ok for a trace residue method in food but not for a pharmaceutical dosage form method). Go to http://www.fda.gov and pick the appropriate Center, then look at the Guidance for Industry issued by that Center.
All standard disclaimers apply. My posts are my opinions only and do not necessarily reflect the policies of my employer.
Thanks for the good point. I am performing analysis of a compound present in a topical formulation, only as an excipient and not the active ingredient. I can not seem to find any FDA guidance addressing extraction recovery RSD's for this issue, but your logic makes sense.
You might try looking at some general method guidelines from AOAC, in that case. Google "Horwitz curve" and you will get some ballpark ideas of what might be accept. The Horwitz equation is for interlab studies--your within lab RSD ought to beat those numbers by a comfortable margin.
All standard disclaimers apply. My posts are my opinions only and do not necessarily reflect the policies of my employer.
Thanks Kindly!
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