Chromatography Forum

Hi guys,

I'm not very familar with thiols in GC analysis and I hoping someone can shed some light on this. I am to start a direct inject method evaluation that contains 5 solvents, two of which are 1-dodecanethiol and dodecanethiol methyl ether. I have no idea of the chemistry of these thiols in the inlet, whether or not these decompose or not.

System is:
Column - Rxt-1701 30x.53x1
Flow - He @ 2.3 ml/min constant flow
Inlet - 265°C, split 15-20:1
Detector - FID @ 300°C
Oven - 45°C for 4 min, ramp 3°C/min to 55°C hold 1 min, ramp 10°C/min to 180°C hold 6 min, ramp 30°C/min to 250°C hold 5-15min

I've never used this column either. The other residual solvents are MeOH, acetone, IPA. Will I have a problem or shall I begin somewhere else?

thiols are acidic and reactive, avoid excessive heat.

a thick film 5% phenyl or 100% methyl silicone might be better although 1 micron 1701 is not a bad choice to start. A G43 column comes to mind.

Do not try porous polymers.

What is your dissolution solvent?

best wishes,

Rod

I did some work several years ago and I seem to recall that they did not have a very good linear response...I think the response was quadratic.

GCguy

Well, lets see. The diluent is DMSO and the method seems to also be implimenting an internal standard (1,4-dioxane). I need to quote this work and if these thiols are problematic, I will obviously adjust the quote accordingly. This is a full validation including linearity. If these compounds are not linear (thanks gcguy), I would need to discuss this with the client.

Rod, how do porous polymers affect the thiols?

Burt

they won't elute from the porous polymers, too large.

The quadratic response GCguy refers to is probably due to concentration dependent reactivity, which may change due to temperatures involved etc.

They should be linear with a FID and if you are not causing any reactions to occur.

best wishes,

Rod

Alchemist5,

You have three very polar solvents and two really heavy thiols. If the 1701 can separate the methanol, acetone, and IPA (and I am not sure if they can), then the 1701 might be a good choice for the thiols. My guess is that both ot the thiols will elute after the DMSO (Rod?)

I concur with Rod, they should be linear since they are mostly hydrocarbon anyway. I think that Gcguy may have been using an FPD.

Best regards.

Should I be concerned with any tailing and/or disulfide formation?

A 1701 should separate MeOH, acetone, and IPA.

Depending upon concentration of the afore mentioned solvents, fronting/tailing could be a real problem.

A thicker film could help with that ... or a higher split raito.