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I am trying to measure the concentration of a Volatile Organic Compound (VOC) inside a liquid using Gas Chromatography (GC). The liquid contains particles that cannot be sent to a GC, so I am using the head-space method (allowing the organic compound to evaporate into the gas above the liquid--- see this link:http://www.chem.agilent.com/Library/applications/5990-3285EN.pdf)--

I let the contents of the liquid equilibrate with the air in the vial at 50 C-- and then I use the air as feed for the GC. However, the concentration in the air is rather small ~ 10-20 ppm. Is there a technique that can be used to increase the concentration of the VOC's?

I have wanted to use a smaller vial to collect my liquid, but the liquid splashes about and contaminates the cap of the vial, which makes me scared to inject a needle into it as I may wreck the needle.

Update

I tried to repeat the experiment with the vial at a higher temperature ~70 C. This lead to the needle clogging. I am unsure of the cause of the needle clogging but I suspect it may have something to do with water evaporating and taking some of the polymer particles with it. Once in the needle, the particles could get dry and solidify.

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Explaining your intended technique a little more clearly might bring in more people with the ability to answer. – dmckee♦ Aug 2 '11 at 19:25
@dmckee, could you tell me where I should expand? – picakhu Aug 2 '11 at 19:29
I had to deduce what you meant by "the head-space method". Admittedly that wasn't hard after I stopped boggling and started thinking, but it never hurts to make things easy for the guy who might help you. – dmckee♦ Aug 2 '11 at 19:30
@dmckee, I think using --'s fixes that. Does the question read better now? – picakhu Aug 2 '11 at 19:33
BTW--If the Experimental or Applied Physics proposal is to go ahead, I think this is the kind of question that would be better there than here. (Of course, I don't see any problem with one site that includes this question.) – dmckee♦ Aug 2 '11 at 20:01
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1 Answer

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Is there a technique that can be used to increase the concentration of the VOC's?

Presumably heating the container (gently!) will work. In the past I have found that a heat lamp is safe when one needs to heat a small quantity of liquid without allowing it to boil. You will--of course--need patience.

I have wanted to use a smaller vial to collect my liquid, but the liquid splashes about and contaminates the cap of the vial, which makes me scared to inject a needle into it as I may wreck the needle.

'Fraid I can't help you there.

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Patience and time I have. I just wish the concentration could be higher. I will try it again tomorrow at a slightly higher temperature, hopefully it will be better. – picakhu Aug 2 '11 at 19:35

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