Purge and Trap issue

[Yama001]

Hi folks, I would like to see if the board can shed any light here on the following:

We use an OI 4660 concentrator with an OI 4551 autosampler and an Agilent 6890/5973. The column is a RTX-624, 0.25mm ID, 1.4 um film, 30 m length. The inlet is set for a 40:1 split, column flow is 1 ml/min. The temperature program is 1 min at 40 degrees, 15 degrees per min to 220, total run is 20 min.

The P&T is set to purge 11 min, dry purge 3 min, Desorb 1.5 min at 240 degrees, bake 7 min at 250. Desorb flow is 40 ml/min, using a VOCARB trap.

When we use this for EPA 8260 work, we routine have trouble with the first two surrogates, Dibromofluoroethane and 1,2-Dichloroethane-d4. The associated internal standard is Fluorobenzene.

We get acceptable initial calibrations, but as samples run, the Fluorobenzene internal standard recovery drops, driving up the two surrogate recoveries. Note that we do not use an internal standard spiking module; we hand spike everything. Note also that the rest of our internal standards and surrogates behave well. The system passes all the leak checks. We get acceptable data when the 4600 is used with a 4552 (Archon) autosampler.

I suspect the hand spiking of the internal/surrogates has something to do with it, but I cannot see where.

Thanks, Tim

[Bigbear]

Could be water building up in the MS. Do the surrogate recoverys improve after the MS "rests" for a while? Do you use the 6mm drawout plate? I used the same setup ( Agilent) for a while, everything was good until everything fell out!
I now use a 20MX0.18X1 column. Column flow is 0.6cc/min and a 150:1 split. This reduces the water getting to the MS. I also set my GC oven to hold at the final ramp temp for 10 minutes, with my P&T parameters the GC is waiting when the P&T is set to desorb. I also set my gas saver to 150 cc/min @ 1.5 min ( I have to desorb for 3) , for your parameters I suggest seting this to 0.8 mi. I feel this dries my transfer line as I have my P&T in series with the GC inlet.

[James_Ball]

Does the first internal standard recovery come in near 100% with the next standard you run then fall off again?

[Steve Reimer]

I see that behavior with my Archon when the seal to the standard vial leaks. It was also very evident when the rotor face in the addition valve was leaking.
How are you injecting the standard mix? Maybe a better question, if you inject one vial and let it sit overnight is the fluorobenzene much smaller on analysis?

[Yama001]

Gentlemen, thanks for your replies. I will be working with the techs next week; I will continue the conversation then.

Quickly, OI tech support emphasizes the water issue, the IS drop is consistent and does not rebound (note - only the first internal is affected). The spiking is done by adding 20uL at 100 ug/mL into a 40 mL vial. Steve we have not carefully checked how a used vial behaves.

It has been tough to see a good track record of what this instrument does, as the tech mostly use it to screen samples and do not pay much attention to results. We are trying to make it a production instrument again, but this recovery issue seems to keep confounding us when we go that route. I refurbish it once or twice a year after the screening wrecks it, then I hassle the techs to be more careful. They are too busy to pay attention and can justify ignoring it as they struggle to get reportable data with this beast. Long term arguement here .

Thanks again folks and have a good weekend.

[James_Ball]

Gentlemen, thanks for your replies. I will be working with the techs next week; I will continue the conversation then.

Quickly, OI tech support emphasizes the water issue, the IS drop is consistent and does not rebound (note - only the first internal is affected). The spiking is done by adding 20uL at 100 ug/mL into a 40 mL vial. Steve we have not carefully checked how a used vial behaves.

It has been tough to see a good track record of what this instrument does, as the tech mostly use it to screen samples and do not pay much attention to results. We are trying to make it a production instrument again, but this recovery issue seems to keep confounding us when we go that route. I refurbish it once or twice a year after the screening wrecks it, then I hassle the techs to be more careful. They are too busy to pay attention and can justify ignoring it as they struggle to get reportable data with this beast. Long term arguement here .

Thanks again folks and have a good weekend.

If you are having a lot of foaming samples on this instrument then that can cause all kinds of problems. Also if you use an anti-foam agent it can gum up the tubing inside the instrument and cause carryover and other problems similar to what you are seeing. After we ran some PVC monomer samples that tend to foam and we were using anti-foam agents also, we had to have EST refurbish our Encon because we were having terrible problems with carryover and very non linear calibrations and the internal standards were not stable. Once they replaced the entire flow path, everything looked like it should again.