Lost alcohols on P&T GCMS

[rv3]

Hello Again Everyone!

I'm having a problem with the alcohols not getting to the GC. I'm running a 5890 S II with a 5972 MSD an Archon Sampler and OI 4560 P&T. We had been having Alcohol resolution problems for a while but didn't think much of it as the instrument was due for maintenance. Then they just disappeared. We're running our waters in soil mode for a variety of unrelated reasons. the first thing i did to check was direct inject 1 uL of our working EtOH TBA standard and sure enough right where they're supposed to be. So far i've done the following maintenance in this order:

1: inlet new liner septa gold seal and column trim 2: New Trap (#10) 3: new transfer lines (sulfinert) 4: new water management unit and assay line 5: new soil purge needle and pencil filters on Archon 6: sonicated the sparge mount and 6-port valve in MeOH replaced the line from the sparge mount to the 6-port valve new sparge tube replaced all valves on the manifold.

After all this i still can't see the alcohols, not even a "might be it" blip. we run the P&T at standard conditions with a 0.5 minute desorb 11 minute purge at 40 C. At this point i have no idea what else to even look at. does anyone have any thoughts?

[ThoSt]

Ok so as far as i got your problem you don't have a peak, do you see any other peaks at all? is the background good? (typical background ions?)

[Steve Reimer]

If you put something more easily purged, e.g. DCM or ACN in the vial do you see that? Are you adding anything from the standard vials on the Archon?

I'm wondering if you are losing the water soluble components along the way, in the Archon or the water management of the 4560.

[rv3]

Ok so as far as i got your problem you don't have a peak, do you see any other peaks at all? is the background good? (typical background ions?)

Yes I have all the other peaks I am looking for, we run 8260B on this instrument and I have the full compliment except for the alcohols EtOH and TBA. One of our internal standards is deuterated TBA, -d9, which is recovering about 20% of the last calibration. Even the Ketones are recovering decently, ~75%, just the alcohols are problematic.

Are you adding anything from the standard vials on the Archon?

We spike in the VOA vial since we're using soil mode, EtOH at 250 ppb and TBA at 125 ppb, about the mid point of the curve. I just ran a 2,000 ppb EtOH and can get something, but it is about 1/20th the area count that it should be. It seems to be getting stuck somewhere but with all the maintenance I have done I figured the entire sample pathway has been replaced, what else could it be?

[James_Ball]

Physically check all the heated zones to make sure they are all working correctly, could be cold spots adsorbing the alcohols.

If the ketones are falling too, it could be the column. I had times where every other analyte looked great but was losing Acetone and MEK(wasn't running alcohols), tried everything. Replaced the column and bang, just as they should be.

[mckrause]

Have you checked your purge flow? I've seen low purge flows give you really low alcohol recoveries, even with ketone recoveries (they're not as soluble).

[rv3]

Have you checked your purge flow? I've seen low purge flows give you really low alcohol recoveries, even with ketone recoveries (they're not as soluble).

You nailed it. i started tracing the flow coming out of the 6-port valve into the trap and it was at 8 mL/min all the way back to the flow control module on the Archon. Which is, at least for me, a first. we'll see if it fixes the issue but i'd guess that going from 8-40 mL/min will make a huge difference. Thanks again all who responded.