Recovery issues

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

3 posts Page 1 of 1
Hi All,
We are using liquid-liquid extraction method with extraction solvent ethyl acetate. We have preformed recovery testing by comparing area ratios of analyte and IS in IS post-spiked (IS post spiked after QC extraction) samples with pure analytical solution. We got 17.4% and 20.4% CV for analyte 1 and analyte 2.
All other tests (Pr and Acc, stability etc.) passed.
We set 15% acceptance criteria on %CV.

According to FDA, recovery should not be 100%, but it should be precise at each level.

Even if the recovery is not precise, because LLE is a technique with high variability, IS can deviate from extraction to extraction: do we need to have criteria on recovery CV, if we are using SIL IS which will compensate for any deviation during extraction?

Could you say how you are doing recovery test?

Thanks in advance
"Could you say how you are doing recovery test?"


Do you dry down your LLE samples and reconstitute to increase concentration?
If you do,
you COULD extract a number of blanks along with your standards and QC's. Then reconstitute the blanks with solution with analyte concentrations equal to 100% recovery, compare to QC's.

Or you could spike the blanks after extraction so that they have analyte concentration representing 100% recovery and compare to QC's.....
Star Stella wrote:
Hi All,
We are using liquid-liquid extraction method with extraction solvent ethyl acetate. We have preformed recovery testing by comparing area ratios of analyte and IS in IS post-spiked (IS post spiked after QC extraction) samples with pure analytical solution. We got 17.4% and 20.4% CV for analyte 1 and analyte 2.
All other tests (Pr and Acc, stability etc.) passed.
We set 15% acceptance criteria on %CV.

According to FDA, recovery should not be 100%, but it should be precise at each level.

Even if the recovery is not precise, because LLE is a technique with high variability, IS can deviate from extraction to extraction: do we need to have criteria on recovery CV, if we are using SIL IS which will compensate for any deviation during extraction?

Could you say how you are doing recovery test?

Thanks in advance



Try a different brand of ethyl acetate. There is a bad batch out there that contains enzymes that attack some analytes.
Don Shelly
LGC Standards
3 posts Page 1 of 1

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