Can a simple household oil less compressor be used for GC?

[lgchrom]

For GC-FID in particular. If yes what is the best way to dry the air before sending it into the purifier. The air here is pretty moist. The lab is close to the sea.

thanks

[chromatographer1]

It sounds like an awful expensive way to save money.

Be that as it may:

Pump the air into cylinders and much of the water will dew out. What is left will be mostly consistent in concentration of water. More of an issue is the trace amounts of hydrocarbons giving a possible noisy baseline on a FID.

Your pumping system and water dewing traps and hydrocarbon traps which are followed by a catalytic converter to remove methane won't be cheap.

If you want to buy a commercial system try one of the process analyzer companies or one of the gas producers companies and purchase a quality system.

If you want quality results you have to pay the piper.

good luck,

Rodney George

[lgchrom]

so what are your alternative more cost effective suggestions?

bottled air?

GC specific air compressor?

any options on the used market?

thanks

[WK]

Hi All,
We have recently been taken off the main factory air supply.
So now we have an oil-less compressor leading to a filter system (large coalescing filter - then a large dessicant filter). When the air enters the lab I have an moisture indicating trap and then fuel gas filters before the GC.
Are you saying that the hydrocarbon trap part of fuel gas filter will let methane pass through?
(I have moisture indication trap too because large traps outside have no indicator).
WK

[larkl]

If you're committed to trying this, I would search the internet for setups (try compressed air for painting). Lots of "home-brewed" systems that can achieve a reasonable dewpoint, think long lines with low point bleeds. Follow this up with a moisture trap and maybe an indicating trap and you might be OK.

[AICMM]

mariosapm,

The simple answer is yes, you can. The more complex answer is that it depends a lot on what you are trying to do. If you are trying to measure low levels then remember that compressed room air has methane in it and it will affect your background signal. (See all the discussion of methane in air and methane in air blanks in this forum.) Remember, too, that fairly high concentrations of complicated mixtures with large splits can start to be down near the noise level. Breathing air was offered up as an alternative at one facility I visited but it too has hydrocarbons. If you are doing very precise work at very low levels, then buy UHP air.

On the other hand, if you are doing high level hydrocarbons then a compressor should work fine, especially if it is a short term or portable application. If so, put a good, large volume indicating moisture trap right before the GC and check it every day. Also, drain your compressor vent every day or two to make sure you don't accumulate too much water in the compressor tank.

Best regards.

[lgchrom]

The air compressor I currently have is a small all-round oil-less generic type of compressor.

The analyses I am interested in include Fatty Acid Methyl Esters, PAHs, PCBs and an assortment of generic applications.

The compressor will not be located indoors.

I would't like to be killing moisture traps each 50 runs of course. They cost a lot as well.

[chromatographer1]

wk

I know of no hydrocarbon trap that will stop methane. If you know of one please post it on the Forum.

Catalytic conversion of methane to CO2 is the only way I know to remove methane from air completely.

If your air is contaminated with natural gas fumes or is downwind from a dairy farm, your levels of methane may vary.

Rodney George

[CE Instruments]

Many of our customers use/used compressors such as the Jun-Air (other suppliers also exist) These are oil free compressors and can be used without filters. Any Hydrocarbon background (Methane) will be pretty constant and will serve only to increase the background noise. For most samples this should not be an issue for low levels and conformation I would advise GC/MS rather than FID. Just make sure you empty the water that builds up in the reservoir

[Stepan]

Many of our customers use/used compressors such as the Jun-Air (other suppliers also exist) These are oil free compressors and can be used without filters. Any Hydrocarbon background (Methane) will be pretty constant and will serve only to increase the background noise. For most samples this should not be an issue for low levels and conformation I would advise GC/MS rather than FID. Just make sure you empty the water that builds up in the reservoir

100% agree. I use oil-free pump from hardware store. 1/2 HP or more is plenty for any reasonable number of GC's (you should expect 3-7L/min of air per every 1 HP). Pump must be able to generate 60 PSI at the exit. It pays for itself, all lines and valves in 4 months.

Our pump works in the storage area next to cleaning supplies: we did not noticed any interferences. We use homemade Silica Gel and Charcoal traps. GC-FID Split/split-less operation. Detector noise level is equivalent to 100 ng/ml injection. Air as good as "Medical Grade Air".

The only limitation: the hardware grade pumps last 1-3 years and when brake can overheat. We do not leave them running when nobody is around.

[Phycal]

PCB's do not burn well - so a ECD is used for detection not an FID.

[Nathan Sharp]

I found a great online resource to browse and compare similar products: http://www.medicalexpo.com/medical-manu ... -7268.html

[MSCHemist]

Could you just use a hydrocarbon filter and bake it out or replace it frequently?

[osp001]

I've been using a Harbor Freight compressor with hydrocarbon and water traps, and it works fine. But I live in the desert, with ~9% RH most days, so I don't expect the moisture trap to do all that much work.

[MSCHemist]

Many moisture traps have indicating material and you can either replace the material in the trap, the whole trap, or bake it out. I'd see if you can get traps that you can either bake out or replace the material cheaply, hydrocarbon and moisture. Still We get charged $60 a pop for zero grade air that compressor

http://www.harborfreight.com/air-tools/ ... 68067.html

is only $200.