I have been extracting organic compounds of my water samples using solid phase extraction (SPE) and evaluating them through various bioassays. I have many different tests to do and I have to keep the extracted samples for sometime. I am currently storing them at 4 degree Celsius and the solvent I used for elution was methanol. Does anyone know how long they can be stored and at what temperature condition?
I actually don't know my analytes since I'm testing effluents. Wouldn't the multiple thawing affect the samples as well?
It all depends on the analytes of interest. Some will be stable and others will not be stable. A storage stability study is often used to determine how the analytes will behave with various storage techniques.
For Pharmaceuticals and Pesticides, we stored them at -20C, to analyse them the next day...
I also would recommend storage at -20C, where Methanol will remain liquid, or if possibly at -80C, if available and if the storage vial is small enough. The rate of degradation should drop. Note however, that some molecules, such as proteins, will lose their 3-D conformation upon freezing at very low temps. This is probably less of an issue for small molecules. As other respondents have said, it really does depend on the compounds and the tests you are doing. Consider control spikes with a known amount of your analytes in your solvent, or if you have a control matrix, matrix spikes, these can provide holding time info that can allow you to estimate storage effects.
If you do not know the type of analyte studied, I would protect him from (1) light (caramel jar or covered with aluminum foil), (2) temperature (-20 or -80 C) and (3) microbial growth (lyophilizing the sample). Additionally, you can try the extracts before and after storing the sample in the freezer. Also, make a trial to evaluate the effect of lyophilization on the biological activity of the sample.
In addition to the recommendations above, I will suggest splitting samples into smaller quantifiable amounts to prevent refreezing thawed samples which seemed to be an added concern of yours. All the best!
Thank you all for all the recommendation. I will do as recommended with regards to the storing. I can't do much evaluation to my samples degradation though since I only have a limited amount and I have many required bioassays to perform on them. In addition, I really have no idea on the analyte present in my samples because they came from municipal domestic wastewater and I am doing a overall toxicity evaluation through bioassays. Hopefully storing them at -20C will help preserve my samples a bit for a few weeks.
Lea, I think that it's very important that you can storea a small sample for future studies of characterization of the analytes because you're going to lost a lot of environmental information (probably unrepeatable).
Might be interesting to answer this question scientifically. That is, take 10 samples via your SPE method, and store them in the freezer at -20 C. Then, each day for the next 10 days, take 1 sample out and analyze it. That way you will learn how the apparent concentrations of your target analytes vary with storage time. If you really made a study out of it, it might even be publishable, but that might require more time than it is worth....
I am also doing like this.May I have the method SPE if you don't mind,please send method to my e-mail ([email protected])
Hi dear Lea,
Could you please share this SPE method with me as well?
Thanks
Due to the volatility of the solvent, shorter storage length, I think is required to maintain the efficacy of the extract.
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