[baglock1]

Caveat: I'm not a chemist.  I'm not a student of chemistry.  The last time I balanced an equation was high school chem in 1995.  With that said, if you go into a long discussion of specific chemical reactions and how they react with other elements you are likely to be rewarded with a post consisting of the single word, "Huh?"  With that said...

I am building a collection device that will be taking atmospheric samples.  My dilemma is collecting the sample while eliminating the possibility of cross-contamination.  There are many different ways to skin this cat, but for the purposes of this conversation let's assume a few givens:

• 1. Air must be drawn through a length of tubing prior to reaching the collection media.
• 2. Fittings will be needed to connect the tube to the collection vessle.
• 3. The tubing must be flexible.
• 4. The tubing will not be cleaned in between samples.

Given that, is there anything out there that meets this requirement?  Ideally, it'd be a length of flexible hose, less than .500" in diameter, internally coated with some compound that contaminants would not adhere to.  At one end, a stainless (or similar, non-reactive metal) fitting would be used, also internally coated if required.  Some limited searching on the internet turned up nothing of value but as I said, my chemistry experience is dated so I may be looking for the wrong thing.  Is there anything out there that fits this need?

Thanks for the help.

Dan

[Mr Peanut]

What components are to be analyzed in the air sample?

[lemonoman]

What about "Undeactivated Fused Silica".  It's used as Transfer Capillary for Gas Chromatography.  Nothing will adsorb to it, and so it won't cross-contaminate.  Your only problem MIGHT be finding it in a diameter large enough.

[baglock1]

What components are to be analyzed in the air sample?

Let's assume that I'm analyzing the composition instead of looking for something specific.  If it was a specific compound I was after, it would be easy enough to find a material inert to that one compound.

What about "Undeactivated Fused Silica".  It's used as Transfer Capillary for Gas Chromatography.  Nothing will adsorb to it, and so it won't cross-contaminate.  Your only problem MIGHT be finding it in a diameter large enough.

Thanks for the tip.  A quick search found tubes in the .5 mm ID range but this is indeed too small as you mentioned.  My sample rate is relatively high so it has to be large enough to support the flow without too much of a pressure drop.  This is definitely the sort of info I'm after however.  If it comes down to it, I might have a intake custom built with this lining.  Thanks for the *delete me*

[Mr Peanut]

Assuming temperature near ambient.

If by composition you mean fixed gases (eg. O2, N2, CO2, Ar) then Tygon will be OK.

If vapor phase organics that will not condense under the sampling conditions are the target then go with Teflon. You will have to clean or replace between samples.

If you are sampling for particulates or organics that may condense try to keep the sampling media at the head of the sampling train (drawing the air directly on the media). Otherwise use glass and rinse the sampling tube into a vial to combine with the media in final analysis..

There really are quite a few possibilities and permutations. There isn’t any “one-size-fits-all” air sampling apparatus. Usually, several techniques need to be employed for a general screening.

Once you get it narrowed down a bit more I would certainly be glad to refer you to a standard method that most closely approximates your matrix, analyte, and conditions.