Chromatography Forum

I am trying to improve the resolution of a gas sample that contains about 13 different HFC and CFC refrigerant components. Essentially my problem is this: I have 5 FID chromatographs, all shimadzu, all different models. I have a standard I use to determine ARF and RRF values. On 3 of the chromatographs, I am able to get good separation of all components with no coelution. However, one machine in particular has been giving me trouble, and I am unable to get two of the components to form separate peaks (they elute as one peak). I have tried everything I can think of, changing one variable at a time, and seen no changes. I even changed the column (identical packing and size just new). Besides carrier flow rate, temperature program, sample size, and column length, even increased sensitivity to make sure I wasn't missing the peak, what else can I try? The two components are R-152 (1,2-difluoroethane) and R-125(penthafluoroethane). Any help would be much appreciated.

Instrument: Shimadzu GC-17A
Column: Supelco Stainless Steel column with Porapak B 60/80, 1/8" x 24 ft,
Detector: FID

Thanks

Check out the AHRI (was ARI) method for R22 using packed column
http://www.ahrinet.org/search+standards.aspx
in standard 700. The example chroms are in AHRI700D. The column, in plain speak, is 1% SP-1000 on Carbopack B 60/80 meash, 1/8" x 24ft. This is a great column for pretty much anything in the world of refrigerants, and a 0.1ml injection gives a good balance of ppm sensitivity with narrow-ish peak width. I had a go with micropacked too but I can't remember how that went.

Yea- that's the exact column I'm using, but I can't get separation between those two components of my AHRI standard.

You said you were using Porapak? The separation is close but does work. Are they small peaks or big ones you're trying to split?

I would ask for another column made with an older lot of packing, or a different lot of packing.

There might be a difference in packing lots, either in the carbon, or in the mesh size distribution.

best wishes,

Rod

My recollections of that column were that it can easily be damaged - at 24 feet, that column must require some fairly high operating pressures?