Do surfactants affect Purge & Trap recovery

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

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I am having a problem with toluene-d8 and chlorobenzene-d5 having low recoveries when surfactants are present in ground water samples. Has anyone else observed this problem?
LALman wrote:
I am having a problem with toluene-d8 and chlorobenzene-d5 having low recoveries when surfactants are present in ground water samples. Has anyone else observed this problem?


If they cause bubbles in the sparger then it is possible they would interfere with the purge efficiency. I know anti foam agents can cause lower recovery.
The past is there to guide us into the future, not to dwell in.
The odd thing is my CC, blank and GRO check all pass. Then I run the same sample 4 times, it will be fine one time and be completely out on one or more surrogates or internal standard the other three times.

I had some samples come in from sites that had been flushed with surfactants and soon after, my peaks started doing this area variation or even double peaking. I've watched one of these purge and they are not foaming. But I wondered if something got on the trap that has got it doing this.

I have swapped in a new trap to see if this problem goes away. I kept thinking maybe my trap was leaking during desorb (because that will do this) and I would check, loosen and retighten or replace the teflon ferrule and it seemed to be tight.

If the trap swap does not work, I may be cleaning lines and/or valves. I suppose it could be sticky valves too. I just got in three new valves yesterday.
A new trap made no difference beyond proving the old trap is still good. I checked out my Tekmar 3000 and although I did not check individual flows, the solenoid valves all seem to be working properly and the total flow seems to be about right.

I'm recalling that I had to replace the proportional valve in an EPC a while back. That EPC is now in my GC-FID. I swapped the GC-FID EPC into my 8260 system because it had a cleaner baseline. I wonder if it is failing and causing variable splitting ratios during desorb? I've put in a call for assistance in testing the darned thing since I don't remember how to do it. There was a timed leak test and another test for controlled column flow with a huge vent flow. I would not be surprise and actually relieved if it failed. This has been plaguing me off and on for a few months.
LALman wrote:
A new trap made no difference beyond proving the old trap is still good. I checked out my Tekmar 3000 and although I did not check individual flows, the solenoid valves all seem to be working properly and the total flow seems to be about right.

I'm recalling that I had to replace the proportional valve in an EPC a while back. That EPC is now in my GC-FID. I swapped the GC-FID EPC into my 8260 system because it had a cleaner baseline. I wonder if it is failing and causing variable splitting ratios during desorb? I've put in a call for assistance in testing the darned thing since I don't remember how to do it. There was a timed leak test and another test for controlled column flow with a huge vent flow. I would not be surprise and actually relieved if it failed. This has been plaguing me off and on for a few months.


5890 or 6890? Haven't had many problems with EPC in 6890s but 5890s can be a real pain. I do have a 7890 that is normally run split with the purge and trap on it, but when I try to do a splitless injection on it now, it just won't hold consistent pressure for the column flow, it bounces a few tenths of a psi and never reaches a ready state. I think that one has a leaking split solenoid.
The past is there to guide us into the future, not to dwell in.
Its a 6890N, I swapped in a known good EPC and the problem of variable IS and Surrogate recoveries persists. Although, oddly, I necessarily had to R&R the inlet while changing out the EPC. For some reason, the intensities of all peaks are 50% of what I had, across the board. So, now I can rule out the EPC for variability. Maybe the column position in the inlet is that critical? I was careful to cool the inlet and transfer line before shutting down the GC for the changeover. And I capped the column. I'm pretty sure I did not oxidize my 5973 MS source.

I think now, that its got to be a flow problem in the Archon or the Tekmar. I ran a couple samples using the Tekmar 3000 glassware. The signals were higher 90% of normal. So provisionally, I think its a problem with flows from the Archon autosampler running in soil mode. I removed and cleaned the needle assembly so I can now rule that out. Tomorrow, I will try cleaning the transfer line and check to see if the in-line gas filters might have been compromised and have too high back pressure. Boy do I wish I had a digital flow meter.
Sunday, I swapped back the EPC since that did not affect flows. I disassembled the Tekmar 3000 and checked lines for free flow and disassembled 6-way valve to check for blockage; It was clean.

NOTE: The little number "1" stamped on the rotor tab should be aligned towards the notch cut out in the bottom half of the rotor body. Much to my disgust, I assembled it wrong the first time.

Found a mostly blocked pencil filter between the flow regulator and the purge needle. I swapped it temporarily for a bulkhead fitting since I had no replacement and I'm using N2 from a dewar for purge gas. Checked the frits in the regulators of the tekmar and the archon. Swapped the green frit in the archon for a spare grey color frit like I have in the Tekmar. Now have full range of purge gas flows. Previously pegging it gave you just over 30mL/min. I still set it for a smidge above 30 mL/min as before.

After all this, I saw no improvement in stability.

I checked the tune on the instrument and found that the 219/69 ratio was about 36%. This is way off the 57% I started at. I retuned (ATUNE) +47EV and set the ratio to 58%. I ran some standards and they were perfect. CCV all 100 +/- 5%. Thought I had this licked.

But I came in this morning and after 10 samples with near perfect ISS recoveries everything went wrong again for the last 10 samples. Checked the 219/69 ratio and its back down to 36% and no amount of retuning will make it better. Despite all ramp curves being smooth and 502 looking pretty good I went ahead and broke vacuum and cleaned the source. Gotta say it looked pretty shiny and not dirty. But I hope this solves the problem.
When was the last time you changed the sample mount on the Tekmar. For a time I ran a Velocity and the mount needed changing every 18 months. Never ran a 3000.
Could it be a water problem? What trap do you use,and steps you take to manage water? Desorb flow controlled by gc? Split inlet? Ratio? Liner?
6mm draw out lens in the ms?
Purge flow is low compared to what 524 specifies (40cc/min).
LALman wrote:
Sunday, I swapped back the EPC since that did not affect flows. I disassembled the Tekmar 3000 and checked lines for free flow and disassembled 6-way valve to check for blockage; It was clean.

NOTE: The little number "1" stamped on the rotor tab should be aligned towards the notch cut out in the bottom half of the rotor body. Much to my disgust, I assembled it wrong the first time.

Found a mostly blocked pencil filter between the flow regulator and the purge needle. I swapped it temporarily for a bulkhead fitting since I had no replacement and I'm using N2 from a dewar for purge gas. Checked the frits in the regulators of the tekmar and the archon. Swapped the green frit in the archon for a spare grey color frit like I have in the Tekmar. Now have full range of purge gas flows. Previously pegging it gave you just over 30mL/min. I still set it for a smidge above 30 mL/min as before.

After all this, I saw no improvement in stability.

I checked the tune on the instrument and found that the 219/69 ratio was about 36%. This is way off the 57% I started at. I retuned (ATUNE) +47EV and set the ratio to 58%. I ran some standards and they were perfect. CCV all 100 +/- 5%. Thought I had this licked.

But I came in this morning and after 10 samples with near perfect ISS recoveries everything went wrong again for the last 10 samples. Checked the 219/69 ratio and its back down to 36% and no amount of retuning will make it better. Despite all ramp curves being smooth and 502 looking pretty good I went ahead and broke vacuum and cleaned the source. Gotta say it looked pretty shiny and not dirty. But I hope this solves the problem.


20% change in the relative of 69/219 is quite large over such a short period of time. Probably shifting the response of the target versus the IS enough to throw off the recoveries. Do you have a hi-vacuum gauge and if so does the source pressure remain steady, or does it rise a little over time, shifting with the shifting relative ratio of the tune? If so it could be too much water making it to the pump. I run a moisture trap on all of mine just before the rough pump that contains molecular sieve to help keep moisture out of the oil, it helps with any moisture passing through the system. On a 5975 I have, I have had to run an overnight sequence of blanks to equilibrate the system before doing a calibration because if it sits too long between sample runs it will "dry out" and needs some run time to become steady again. Once it gets equilibrated with some moisture it will run steady for days if running non-stop.
The past is there to guide us into the future, not to dwell in.
I indeed have noticed something like that. When it has not run over the weekend or for several days; I run a "BFB" to wet everything up again. I had noticed that CCV's tended to pass better if a couple samples had run and figured it was a "trap" thing. But I have noticed that on such days, vacuum is 3.2E-5 mTorr or lower.

Right now a couple days after the source cleaning I am still seeing absolute pressure of 5.0E-5 mTorr yesterday, 4.2E-5 mTorr today and it runs best when it gets down around 3.5E-5 mTorr. Air and water checks are <1% and background is 1000 counts of mostly mass 44.

Also, I may be getting more water on the trap after finding that clogged purge gas filter in the Archon and replacing it with a bulkhead.

I think I have found yet another source of variation, confirmed by my vial supplier. Apparently my last 8 cases have septums that were not glued but were also too soft so they deform easily even though the autosampler needle is quite sharp. I have noticed before that the slightest leak (say a grain of grit in the cap) will cause large losses. They are sending me new caps for my remaining cases and assured me that the new cases have stiffer better sealing septums.
I have had chipped vial tops that caused similar problems due to leaks so that could be one problem. I have also had the purge needle on the soil position on an Archon become clogged with soil or other types of polymer sample we run that caused flow problems during purge. We made an adapter to connect the gas inlet line of the needle to an HPLC pump, and used the high pressure to blow out the plug as sometimes it was just too tight to remove by sonication or simple flushing. It was either that or wait for a new needle to arrive. You definitely need some type of flow meter to check the flow when using the soil purge position even if it is a soap bubble in a burette. I made one like that using a Tee connected to the tip of a burette with some tygon tubing and tubing going from the side of the Tee to the gas outlet and a an eye dropper bulb filled with soapy water attached to the bottom of the Tee. Makes it easy at 40ml/minute since it will take almost a minute for the soap bubble to travel up to the top of a 50ml burette.
The past is there to guide us into the future, not to dwell in.
I use another approach to water mitigation.
I do EPA 524 which says "desorb for about 4 min" I desorb for 3 min and at 1.5 min., I set my gas saver to 150 ml/min. I then hold the oven at the end ramp for 10 min. This way the oven is set to go just before the P&T ends it's dry purge step. I only have one P&T in my system. I timed how long it took for the oven to get to ready after the run stops. Your times may vary.
Bigbear wrote:
I use another approach to water mitigation.
I do EPA 524 which says "desorb for about 4 min" I desorb for 3 min and at 1.5 min., I set my gas saver to 150 ml/min. I then hold the oven at the end ramp for 10 min. This way the oven is set to go just before the P&T ends it's dry purge step. I only have one P&T in my system. I timed how long it took for the oven to get to ready after the run stops. Your times may vary.


Another reason I want to switch to 524.3 is because they dropped the 4min desorb requirement. 1 minute is now the low end of the acceptable range with I think 0.5 being acceptable as long as you show proof you are not losing analyte recovery. 4 minute desorb as been obsolete for over 20 years since people switched to VOCarb3000 traps and using the Split inlet instead of direct connection to a 0.53mmx 105m column with jet separator. EPA is just now catching up with technology :)
The past is there to guide us into the future, not to dwell in.
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.
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.
The past is there to guide us into the future, not to dwell in.
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