Chromatography Forum

I just swapped out an Old DPM 16 port autosampler for a Not As Old Archon hooked up to an OI 4560 then on to an HP 5890 with an FID running in soil mode. It initially had a relatively small "solvent peak" (I've never really been able to figure out what it is but it comes out the same time as my C4 marker) but with the switch over to the Archon it has gotten huge

This is a before picture from the 16 port


And this is the Archon


where the red line is is the largest peak in the first image. The only real difference I can think of is the heated purge from the soil cup, I've turned that off and am waiting for results. Has anyone seen anything like this before or have any idea what this peak might be?

Update: turning off the soil cup preheat did nothing.

Added info i just though of:
I went from purging 5 mL on the DPM to 10 mL with the Archon both for 11 minutes. Is that a possible cause? With the OI water management system i wouldn't think it would have that much of an effect. we use the same Autosampler/P&T combo for our GC/MS set ups and have no major issues with water.
I am using butadiene as my C4 marker if that matters. We also have a Centurion autosampler that is having similar issues with the soil mode operation, could it just be inherent to the mode?
Unfortunately we need the soil side to work for air analysis.

I'm starting to think the peak is MeOH. Our standards are prepared with MeOH as the solvent and it appears to increase linearly with the amount of standard added. Going to purge a vial with only water and then one with a few uL of MeOH and see what we get.

Posting the conclusion in case this happens to anyone else. It is MeOH that is coming from the standards. No idea why the old DPM 16 port didn't pull as much over but we doubled the concentration of the standards to reduce the MeOH and it seems to be workable.

Did the DPM use the long sparge tubes like the Tekmar 2016? If so, it may be the MeOH was condensing on the cold tube, while the 40ml vial in the Archon has less area for it to condense on. Also be sure to turn off the internal standard injection on the Archon, and if you are not using it, leave the vial empty or fill with DI Water, since they can leak. If it is filled with MeOH it could be leaking into the soil sparging system and giving the extra MeOH.

Thanks for the input @James_Ball it was using the longer tubes and that likely had something to do with it. As for the Archon i have gutted the water mode side of the system and bypassed all i could. We're just using the soil side, there's less maintenance, though more prep work, and the LOQ we get is sufficient. The biggest effect was changing the trap type, we went from a Tenax only trap to a BTEX specific trap and it's been great.