Do surfactants affect Purge & Trap recovery

Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.

20 posts Page 2 of 2
What I don't get is how you can do a respone factor calibration with a bottom value that is that noisy without ruining the whole curve.
James_Ball wrote:
Bigbear wrote:
I looked at .3, but was not impressed with all the QC requirements. Matrix spikes again?? Did enough in the past to see that drinking water matrices had no affect on VOC's.


MS/MSD has not given me problems with .3 but having to analyze the low CCC immediately after the calibration and hit +/-50% can be tight and also doing the MRL test. Once you do get the system to run those two checks though, you are confident that you are actually reporting true non-detects and that hits just above the MRL are accurate. I don't like going to CCV every 10 samples instead of 12 hours, but you don't have to check the tune unless you recalibrate so that saves you one injection at the start of each day, though I normally run one just to wake the instrument up.
I have BFB and the other surrogates in my internal standard mix (allowed for 8260). With optimization, I was able to get BFB separated 0.05 min from isopropyl benzene on a 20m x 0.18mm x 1um DB-VRX column. So, I can do a tune check on my 40 ppb CCV.
This has been a perfect trifecta of converging problems...

Last weekend we stripped down the Tekmar 3000 unit. We removed and tested the sample, vent, bypass, and hpc solonoids and associated lines. After that excercise, the system was holding pressure and showing proper purge flows. It worked great for a few days. Then it started dropping surrogates again. Trap back to apparently not holding pressure. After fiddling with the trap a couple times (unsucessfully); I decided to take the trap assembly out of the problem. I short circuited the trap and bottom assembly by bridging the two ports on the 6-port valve with a used moisture control loop. I was still not getting any pressure. I checked for leaks and its the 6-port valve. Apparently the seal is failing. It would seal for some samples and leak for others. The air leakage into the valve might be the cause for tuning drift. Although, air and water checks were always under 1.5%. Last night, I swapped the 6-port valve from an idled 4560 P&T unit and this problem I think is now solved. Air and water check is now under 0.4%.

I'm not absolutely sure but this may have been the root cause of most of my recent problems with this unit and GC-MS.
I have one older Evolution that the 6 port valve will stick about once a month. Gives a front inlet shutdown error because it blocks the flow long enough to shut it down. When we are lucky it happens on the tune shot and stops the run at a very good position, other times it stops it just after the CCV :(
The past is there to guide us into the future, not to dwell in.
James_Ball wrote:
I have one older Evolution that the 6 port valve will stick about once a month. Gives a front inlet shutdown error because it blocks the flow long enough to shut it down. When we are lucky it happens on the tune shot and stops the run at a very good position, other times it stops it just after the CCV :(
I called Valco and resurfacing the valve is pretty reasonable. A new valve is $600 but resurfacing is $165. Is your valve sticking or is it the valve rotator? might be time to investigate getting a new switcher. Although, with that low a frequency, and volatiles seem to be robust enough to be restarted the next morning; maybe its not worth the trouble.
20 posts Page 2 of 2

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