I need some help with some poor separations that I'm getting

[chromatics]

The PI in the lab I'm working for has commissioned me with the task of creating standard curves of GC chromatographs of acetone, acetonitrile, and ethanol with water as the solvent. An easy task in and of itself, but I can't for the life of me get any sort of separation between them. Their retention times are nearly identical and I'm getting no baseline resolution. I've lowered my carrier gas flow (from 2.2 mL/min to 1.0 and 0.5), adjusted my inlet temperature (70, 110, and 220 degrees C), and have tried all sorts of oven temperature gradients (starting as low as 30 degrees C and as high as 70 for four minutes, and then finishing at 110 for four more) with little luck. Normally I'd report back to my boss, but he's on vacation this week and I'd like to have some data for him when he comes back. Any advice, chromatographers?

FYI I'm using an Agilent 6850 GC with an FID detector and helium as my carrier gas.

Thanks for all your help.

[Karen01]

What column?

Are you using headspace? If so which sampler/loop size (if that type) and what is your split ratio?

FYI: This was done by Isothermally by static headspace:



- karen

[chromatics]

Agilent DB-1ms (dimethylpolysiloxane stationary phase). No on headspace, but my split ratio is 200:1.

[Karen01]

Never used that column... Sorry.

The reason I mentioned headspace and split ratio is that i was wondering if the sample was getting on the column in too big a band.

Maybe try injecting less?

- karen

[Peter Apps]

You need a column with a different stationary phase - check out column manufacturer's websites to find one that can separate the compounds that you are interested in - at a guess a PEG (wax) phase or a 50% phenyl might do it.

Peter

[fsistere]

Hi
Try a DB-624 column (or similar), very good for volatile compounds
And isothermal temperature programe.