Chromatography Forum

I have capillary columns and a Varian ion trap with Combi-pal auto-sampler. Have been requested to quantify a few ppm hexane in THF. Cannot see hexane by 1H NMR. Hexane bp 88.7 THF bp 66C.
Suggestions for parameters? Thanks.

I haven't done this particular anlaysis before, so I'm just guessing. We also use a Varian Saturn 2000 ion trap system here, it is extremely robust.

Do you have an 1177 injector, a 1079, or both? If you have the 1079, I must suggest you can temperature program the injector to get rid of the THF and keep the hexane around. If you injected with the 1079 temperature set at 64C, set the split ratio to 100:1, and allow the system to remain in this configuration for approximately 1 minute after injection. Then, at one minute, program the split vent to close and heat the injector at 200C/min to say 280C. Make sure to set your column oven at 64C isothermal for at least the first two minutes of the run, then start a slow temperature ramp to elute the hexane.

Not sure if you will also loose the hexane during the initial injection with the injector at 64C and 100:1 split, but it's worth a shot?

-Aaron

Do you have a FID detector?

And do you have a PEG column like a Supelcowax?

The analysis would be straightforward if you did.

best wishes,

Rod

I have both 1079 & 1177. Have a Supelco WAX, but no FID.

If I connect the Wax to the 1079 and run it to the MS, would you agree with the 1st suggestion as far as methodology?

Also, is there another suggestion for column to the MS (an MS column?)

Thanks!

I think THF and hexane will travel together during volatilization.

Hexane will elute before THF on a Wax column so an injection of a large amount of THF is possible. With a FID there would be no problem with detection at ppm levels, even ppb levels.

best wishes,

Rod

Why not run the detector in selected/single ion mode? The seperation would not be so critical then.

Not having good luck at all temp-programming injector. THF is not pure. Cannot discern hexane from other baseline peaks.

Not running in SIM because: 1) molecular ion is small compared to fragments 2) one of the prominent fragment clusters is common to THF & the other is around 57 (which is pretty common). I thought maybe CI and look for m/z 87.

I'll come back to this later, but need to work on something else right now.


QUESTION: what's the advice on running a WAX to an ion trap MS? (

I'm using a 60m SPB-624 with 1.4µm film and have 6.5 minutes of separation between Hexane (16 min) and THF (22.8min). The oven is at 40°C for 20 minutes at the beginning of the run. This is headspace, but I would not expect the relative retention times to shift all that much with a direct injection.