GC/MS partial recovery loss

[rv3]

Hello All,

I'm having a strange issue with one of my Purge and trap systems. I am running EPA 8260 method on a 6890/5973 with an OI 4660 concentrator and Archon 8100 auto sampler. What has been happening is a loss of about 75% intensity on the first 2/3 of the chromatogram. Once we hit the heavier substituted benzenes, starting with ethylbenzene and going through 1,3,5-trimethyl benzene, the recoveries return to normal. All the internal standards follow the same trend. I've exhausted my knowledge on what could be causing this.

so far I have changed the trap, we use #10, changed the Sulfinert transfer lines the water management unit sonicated and baked the 6-port valve, sparge mount and 4 way cross filter. I have also replaced the pencil filter and purge needle for the auto sampler and finally I swapped the Volatiles Interface for the GC inlet.

I spent a few runs watching the pressure, flow and temperature readings on all parts of the system and everything is normal. I've also tried using both an electronic leak detector on external pieces and a duster can on the MSD seals and found nothing leaking.

An interesting note is that a few days ago the first calibration check, which we run at 25 ppb, would recover great and all subsequent runs were back down to 25% in the first 2/3 of the run and now even the first after a nights rest is showing the symptoms.

At this point I'm out of ideas. any insight would be hugely appreciated.

[gurlwithgcms]

I'm glad you posted this. I've actually been having similar troubles, but my loss is at the end- at bromoform and on. I, like you, changed the pencil filter, trap, sparger tube, and checked for leaks. I also ended up cleaning the source and switching out a filament because one looked busted. But no improvements. The only other thing I was thinking of doing is redoing the tune. Or a new column?

[James_Ball]

Take a look at the BFB tune checks from when the instrument was performing as it should and now when it is not. See if the balance of the high and low masses have changed since then. If 50 and 69 have decreased versus 95 and 174 has increased versus 95, then you would see a drop in the early eluting compunds, if the opposite is true then you will see a drop in the late eluting compounds. The limits are pretty wide on what passes so you can get quite a shift just because the mass balance of the tune has shifted.

Also are you running turbo or oil diffusion high vacuum pumps? Do you have a molecular sieve moisture trap just before the rough pump? What is your split ratio at the inlet? When was the last time pump oil was changed?

Those are just some of the starting points I look at when having such a problem.

[rv3]

If 50 and 69 have decreased versus 95 and 174 has increased versus 95...

Also are you running turbo or oil diffusion high vacuum pumps? Do you have a molecular sieve moisture trap just before the rough pump? What is your split ratio at the inlet? When was the last time pump oil was changed?

Those are just some of the starting points I look at when having such a problem.

Thanks James_Ball i hadn't considered a tune issue. I ran through the last few weeks of tunes and the 50/95 ratio is consistent, 15.5-16.7%, and the next closes 75/95 is also consistent between 45-48%. The abundances have been regular as well.

As for the pumps it has a Turbo for the high vac and Pfeiffer 2.5 for the rough, we do have a molecular sieve trap and i changed the oil about 3 months ago, it hasn't been in production long.

I'm running 50:1 split ratio at the interface with 0.8 mL/Min with a 30mX250umX1.4um Restek column I installed in May.

I'm off to run an Air/Water check and try a new tune and see how that goes. Thanks again for the input!

[01310040231]

You did not mention how old your water management is. We use the same system and we change the water management every three months. The way the water management is designed on this system, it makes it very difficult to clean. We rinse the sample path every week.

[gurlwithgcms]

If 50 and 69 have decreased versus 95 and 174 has increased versus 95...

Also are you running turbo or oil diffusion high vacuum pumps? Do you have a molecular sieve moisture trap just before the rough pump? What is your split ratio at the inlet? When was the last time pump oil was changed?

Those are just some of the starting points I look at when having such a problem.

Thanks James_Ball i hadn't considered a tune issue. I ran through the last few weeks of tunes and the 50/95 ratio is consistent, 15.5-16.7%, and the next closes 75/95 is also consistent between 45-48%. The abundances have been regular as well.

As for the pumps it has a Turbo for the high vac and Pfeiffer 2.5 for the rough, we do have a molecular sieve trap and i changed the oil about 3 months ago, it hasn't been in production long.

I'm running 50:1 split ratio at the interface with 0.8 mL/Min with a 30mX250umX1.4um Restek column I installed in May.

I'm off to run an Air/Water check and try a new tune and see how that goes. Thanks again for the input!

My pump/oil situation is the same as rv3. I looked the tunes and there was some decrease like James Ball suggested. I re-tuned using atune instead of tune wizard like I usually do. The new calibration looked good (all but 1 was on average of response factors instead of linear) and the LCS was within 5% recovery for all.

[rv3]

The Atune seems to have cleared things up, Thanks James_Ball. I never would've thought about the tune.

You did not mention how old your water management is...

01310040231 This has been an issue for us too. We have a monthly maintenance program that includes sonicating and baking out the Water management unit and various other bits and pieces, that really helps cut down on down time.

Thanks again everyone!

[rv3]

And it's back. the system was stable for a couple runs then the middle of the chromatogram fell out. vented the system and cleaned the source and replaced the filaments. after getting everything back up i had one solid recovery and everything dropped out again. Any suggestions?

[rv3]

And it's back. the system was stable for a couple runs then the middle of the chromatogram fell out. vented the system and cleaned the source and replaced the filaments. after getting everything back up i had one solid recovery and everything dropped out again. Any suggestions?