[tsd3]

Hi Everyone-

 I am a graduate student working on the chemical ecology of a yeast - fungus interaction. We have recently learned that our yeast colonies are producing carbon disulfide (CS2) in headspace, and we are trying to test how this compound influences fungal growth.

 The problem is:

  Since CS2 is extremely volatile, we need to dilute CS2 with another compound so that we can achieve a reliable elution rate. Our colonies also produce ethanol in headspace, and CS2 is soluble with alcohols.

 My question is:

 How would I go about creating a dilution of CS2 that I could get a reasonable elution rate from, maybe somewhere in the realm of 0.1 M? Or can we just combine by volume (eg 1% solution of CS2). Also, what is the appropriate compound to mix it with? We are nervous to foul up since CS2 is pretty toxic.

We are just biologists pretending to be analytical chemists, so any help would be greatly appreciated!

 thanks,

 seth

[Mitch]

Do you flow any gases to your colonies or just leave it to air? I was thinking you could bubble a gas through the carbon disulfide to enrich the air around the colonies. A picture of your setup would be beneficial, we're chemists not biologists.

[tsd3]

The basic setup is as follows:

 We are using partitioned petri dishes, with growth medium on one side and empty on the other. The side with growth medium has a standard amount of fungal colony placed on it, the blank side has a 2 ml microcentrifuge vial with either water, ethanol, d-3-carene, or (hopefully) CS2 or a CS2/Ethanol solution.

 A tiny hole has been burned through the top of the centrifuge tube to ensure that the compounds elute. We have had no trouble getting reliable rates with ethanol and d-3-carene, but the CS2 elutes in minutes.

 The idea is that the (synthetically derived) headspace volatiles are influencing fungal growth in some way. We performed the exact same experimental design using partitioned petri dishes with fungal colonies and yeast colonies, and showed that the presence of yeast-produced volatiles enhanced fungal growth.

 When we performed a GC of the headspace volatiles produced by yeasts, we came up with ethanol, d-3-carene, and CS2.

 Thoughts? Our main problem is just making a CS2/Ethanol solution, or finding some way to work with the CS2 so that it doesnt elute within minutes. Ideally the solution or compound would volatilize gradually over about 15 days.

 thanks.

[demoninatutu]

I'm not sure how reliable/reproducible it would be but it sounds like a membrane would be worth a try. Something like cellophane or parafilm stretched thin.

[DrCMS]

Please stop using the word elute when you mean evaporate.

http://en.wikipedia.org/wiki/Elute

[tritiger]

you can titrate it by KMnO4 after dilution.