How to calculate extraction efficiency

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

8 posts Page 1 of 1
I'm looking for any methods/literature that can be used to calculate the extraction efficiency of various extraction methods. I would like to determine how efficient current extraction techniques are that are being used to analyze specific analytes in plant samples.

Unlike with soil samples I cannot spike the matrix.
Welcome to the forum.

If you cannot add a known quantity then an alternative is to do the extraction twice on the same sample and compare peak areas - the area of the peak from the second extraction as a fraction of the area of the first peak is the fraction of analyte that was not extracted by the first extraction.

Peter
Peter Apps
Thank you Peter. The extraction consists of 200mg plant tissue and 10 ml of solvent. For the second extraction would I just pour off the remaining solvent from the first extraction and then add new solvent to the vial?
You have to be very thorough in removing all the solvent from the first extraction, because it contains extracted analyte that will show up in the second extraction.

You cannot remove the last traces of solvent by evaporation because that will just put the extracted analyte back into the sample.

Peter
Peter Apps
Thank you, that was the issue I was wondering about. I wasn't sure how to completely remove the solvent from the first extraction. I'll try pouring out the solvent and try to drain the remainder under a slight vacuum.
I'm actually working on something like this now. It is likely that you won't get it all in one extraction anyway so it doesn't matter so much that you can't remove all of the residual first extract. Just do the best you can. You will probably end up pooling your extracts in the end.

I am using a water soluble solvent (methanol). I extract once (mix sample + 10 mL MeOH in a centrifuge tube, close the tube and sonicate for 10 minutes), centrifuge the sample to get the solid material to go to the bottom of the tube, thus making it easier to remove the solvent with a glass Pasteur pipette. Don't disturb the bed of plant matter as you remove the solvent. Repeat and keep the individual solvent layers separate. My plant material is very concentrated in "oil" so I take 1 mL aliquots of the individual extracts and dilute them separately to 100 mL with water. When I analyze for the volatiles in the solvent/water mixes, I see successively smaller amounts of the analytes in each extract. I carry this out until I get what I want out (usually 99% on the most difficult material to extract). That tells me how many times I need to extract the sample to get quantitative recovery. I was able to get 99%+ in 3 extractions (0.26 g plant matter and 10 mL shots of methanol). I pool the 3 for subsequent, more comprehensive analyses.

If you have a particular target molecule that is more easily extracted and you don't really care about the rest, then you might not have to extract as many times. Some analytes in my mix are no longer detectable after the first extraction but I can still detect them in the pooled extract. Good luck!
Hi

I don't know how relevant this is but the experience/analogy that I have is of the extraction of fluoride from toothpaste with water.

It is a triple extraction.

The first extraction of 0.6g of sample with 10mls of water after mixing will extract 90% of that which it is possible to extract

Centrifuge and decant.

Add a second aliquot of solvent and repeat - that removes a further 90% of that which it is possible to extract

Centrifuge and decant and combine with the first extract = a running total of 99% of total extractable material

Add a 3rd aliquot of solvent and repeat - that removes a further 90% of that which it is possible to extract

Centrifuge and decant and combine with the the other 2 extracts = a running 99.9% of total extractable material

So, in this example a triple extraction with the best solvent is efficient but please note that this is the total amount of extractable material and not necessarily the amount of target analyte in the sample. Some will always remain adsorbed on the silica abrasive.

For toothpastes there were 3 measurements
Total amount in the sample
Total available by triple extraction
Available fluoride under the conditions operating in the mouth, which is not exhaustive.


Regards

Ralph
Regards

Ralph
Hopefully, it is obvious that you can't use so little solvent that the plant matter absorbs it all in the first extraction. The solvent must be in a fair excess - like what I've described in my experiment.
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