Chromatography Forum

hi,

We are running Thermo trace 1310 GC-FID. We couldnt get benzene peak. Could you please recommend GC condition. We used NIOSH 1501 method and no success.

thank you very much in advance,

Regards,
Mungun

It has a rather small retention index coming off at 650 or so on db-1 column (same area as hexane so the solvent peak (what solvent are you using) could cover it up. A thicker film would be better.

642 DB-1
648 OV-1
663 CP-Sil-8CB
936 Supelcowax-10™
938 DB-Wax

Liquid injection or headspace?

I get excellent retention and peak shape for benzene on a Rtx-624 (Restek). The one I use most is the 60 m x 250 µm x 1.4 µm version. It's a thicker film (MSChemist's suggestion) so if you have late eluters, it might be problematic. My conditions:

Inlet: 240 °C, helium carrier gas at 15.5 psig
Oven: 40 °C for 2 min. 40-240 °C at 10 °C/min., 240 °C for 18 min.
Detector: FID, 30:300:25 H2:Air:helium makeup, 240 °C

99% of the time, I'm sampling the headspace. Usually solid-phase microextraction.

It has a rather small retention index coming off at 650 or so on db-1 column (same area as hexane so the solvent peak (what solvent are you using) could cover it up. A thicker film would be better.

642 DB-1
648 OV-1
663 CP-Sil-8CB
936 Supelcowax-10™
938 DB-Wax

thank you, we use TG-Wax MS column (film thickness is 0.25) and methanol as solvent. Do we have to use thicker column?

Liquid injection or headspace?

I get excellent retention and peak shape for benzene on a Rtx-624 (Restek). The one I use most is the 60 m x 250 µm x 1.4 µm version. It's a thicker film (MSChemist's suggestion) so if you have late eluters, it might be problematic. My conditions:

Inlet: 240 °C, helium carrier gas at 15.5 psig
Oven: 40 °C for 2 min. 40-240 °C at 10 °C/min., 240 °C for 18 min.
Detector: FID, 30:300:25 H2:Air:helium makeup, 240 °C

99% of the time, I'm sampling the headspace. Usually solid-phase microextraction.

Thank you very much,
it is liquid injection. Only difference from yours is the column length and film thickness. Do we have to buy another column:(

It is certainly an option. We run water samples for VOC's on a thin-filmed wax like this and it doesn't give the best peak shape for benzene. I've done benzene on a wax (30 m x 530 µm x 1.0 µm) with a flame detector before with good success (SPME sampling):

http://s1285.photobucket.com/user/rb6ba ... g.html?o=2

The phase ratio for the thin-filmed wax might be too large:

http://www.separatedbyexperience.com/li ... aspx?id=34

For your column (250 µm i.d.) it is 250. For my column (mentioned above) it's 132.5. That means in my case, there's more stationary phase in the column compared to the inner diameter of the tube. For the Rtx-624, the phase ratio is 44.6 (lots more stationary phase compared to the volume of the tube).

I did this really quick. Gives you an idea of the peak shape I'm getting on the Rtx-624.

http://i1285.photobucket.com/albums/a59 ... gsrrgi.jpg