Chromatography Forum

Hey all,

I need to take a sample from an exhaust vent off of a water treatment skid and try to ID methanol, methane and maybe any other VOC. I have never done any air sampling before. Only things I have onsite are 25 mL headspace vials and gas tight syringes. I have a 30m Stabiliwax column that I am planning on using.

I will probably take a sample for a few seconds in the exhaust stream, and a background sample far away. This is going to be a crude test. Any thoughts/help? Thanks

Are you using FID?

If the air is humidified a water peak will be close to the methanol. The hydrocarbons C1-C4 will have almost no separation, and their 'plug' may be distorted or 'flattened' by a large amount of water or methanol.

Methanol should elute after THF, acetone, and methyl acetate and almost coelute with MEK.

DCM should elute after methanol.

Good luck hunting.

Rod

Yes its FID with a SSL injection. I have another GC with On column injection port but my needles don't fit the stabiliwax ID. So i have to use the split splitless. I was afraid this column wouldn't separate the low carbon volatiles... and i forgot that water can interfere on the fid. There will most likely be some moisture carry over. I guess I will have to use something like a VOCOL column?

Vocol, or 1301 is a better choice, me thinks.

The water interferes at the head of the column, not so much at the FID end. But only if it is a large amount (steamy air would qualify). If it can separate at the head giving a narrow plug, it may spread out the hydrocarbons which will tend to smear as the HC won't retain forming a plug until they pass the water plug. (water and oil don't mix, right?)

good hunting

Rod

How about a PoraPLOT Q or similar? Should separate out the light components?