By sampling headspace of plant volatiles by using PET oven bags we have sometimes measured contaminations by decanal and occasionally by different plant volatiles. Did you make similar experiences with such contaminations? We think the decanal is directly emitted by some charges of PET foil, while plant volatiles seem to penetrate the foil. This could be caused maybe due to quality differences of the product.
Hi Jurgen,
We use Teflon or Tedlar bags to minimize possible contamination (see J Agric Food Chem 2008 56, 2759 or 2009 57, 3749). We have not noticed decanal from our bags or SPME fibers. Have you run a blank control to confirm that it is from your bag, solvent/SPME, or from your ad/absorbent? We have noticed decanal as a fatty acid breakdown product. Does your matrix possibly have any fatty acids?
Good luck.
John
Hi Jürgen,
I have also had contamination problems and have used glass vials instead of plastic bags. Of course that means more cleaning and originally buying vials but you should not have any contamination then.
Bis bald
Taina
Hello Jürgen,
we also encountered problems with contamination using Tedlar bags which we were able to reduce by repeated conditioning of the tedlar bag with clean air at increased temperature. Partners however prefer cheaper PET-oven bags, claiming that they (after conditioning with clean air at elevated temperature) contain much less contaminants than the tedlar bags. In both cases contaminations with decanal were not observed.
Depending on the concentration range you're looking at neither Tedlar nor oven bags would be sufficient. If you go into the ppbV - range it might become necessary for you to use canisters instead.
Greetings,
Christopher
Hello Jürgen,
Decanal is a volatile compound which is present in PET as others alkyl adehydes. It could be leached out and contaminates the stuff in contact.
Moreover you used PET-oven bag, maybe these bags are plasticized to render them flexible. So in this context, glass transition of PET is lower and tranfer of volatiles is emphasized in the other way, from plant to polymer material, as you mentioned it :"while plant volatiles seem to penetrate the foil"
Maybe it is better to use canisters as Christopher mentioned it.
Have a good day
Some papers to read about PET/volatile compounds:
Bach et al., Water res, 2012, 46, 571-583
Ducruet et al;, Food Addit contam, 2007, 24, 1306-1317
Fabris et al, Food Sci Technol.2010, 30, 1046
Kassouf et al, Talanta, 2013, 115, 928-937
I do not understand. What is PET? polyethylene terephthalate?
I guess so, sample with those bags always contaminate plants. In case you do volatile sampling is best done in glass, no phthalates but to a lesser extent. I have a glass jar for potted plants adapted to volatile plant foliage is sampled only and is not sampled the soil. Do you want me to send a photo?
I agree, Decanal could be from fatty acids. I have attached a picture of some data we took to a conference a couple of years ago. It is flux of 2 compounds through several films and thickness. Tedlar, PET, and some commercially available refuse bags were used. We were trying to see if compounds were trapped on the film or if they were moving through the film.
Here decanal comes from processing of PET as the others alkyl aldéhydes present in the polymer.
Optimization and increase of the barrier properties of dense polymers as PET, polyolefins etc..towards organic molecules is a challenging task where we are involved in our research group. To decrease permeability , action can be done on diffusion coefficient and solubility coefficient. Different levers exist to decrease the diffusion coefficient however the action on solubility coefficient appears more complex.
Hi Violette,
thank you very much for your huge amount of information regarding my problem. It seems that you are very experienced in asessment of polymer foils. This is very helpful. I am currently attending a meeting and have no possibility to read the papers you mentioned, but I will do next week. I will talk to you later.
To all,
thank you very much for all the ideas and recommendations. Unfortunately I am working with trees and I cannot out them in glass vials but have to wrap the twigs in a foil (Taina, Violtte). But a pretreatment as suggested by Christoph could be helpful. Or change to other foils as Teflon suggested by John.
Dear Norma,
yes PET is polyethylene terephthalate. I am very interested in a photo and description of your modified glass jar sampling system for potted plants. I would be happy if you could send. Best regards
I send a study presented at a conference, here comes the photo. The article is not yet published. For Dynamic Headspace, the basis for separating the floor of the container is a square of acrylic with a hole to let the stem, the glass on top has a clean air inlet and outlet Super Q trap to catch Headspace compounds. The flow is provided with a vacuum pump, is controlled by a flowmeter (1L/min).
For static headspace, you can collect with a SPME fiber.
Best regards.
Hi Jurgen,
We have been using glass-jars for collection of volaitles from plant source. Its easy to handle and contamination-free mostly, apart, its easy to decontaminate. However, we have also had decanal. However, as per previous comments above, i think its the degradation of certain acids in the plants mostly. A control would be pivotal in such cases.
best regards
Hi Andreas,
I hope everything is alright!
Thanks a lot for your many helpful comments and also the article.
Dear Jürgen,
we use glass vials for headspace collection and still get both decanal and nonanal as contaminants; we also use push and pull, thus introduced clean air into the collection chamber, thus it is a bit of a mystery for us where they come from...
Glass vials can still affect your headspace sampling, e.g. by adsorption. You can deactivate the glass adsorption sites using silanization (e.g. you can wash the glass with (3-Aminopropyl)triethoxysilane in aceton).
All the best,
Dear Florian,
When you said that you introduced "clean"air , how are you sure that it is clean as compressed air can be polluted by pumping ssystem as an example tubing made with PVC or Polyolefins.
Regards
Hi Loic, Violette,
yes silanisation is importnat, we use Sigmacoate, a ready to use solution from Signal Aldrich. We also filter the incoming twice with activated charcoal, so i guess it can be considered "clean".
F
Hi, I think you can identify and remove the contamination by comparing headspace collection of your sample with a control sample (without plant), with some replicates of course.
Dear all,
I want to thank you very much for your very helpful comments!
Cheers, Jürgen
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