Chloromethane/Bromomethane contamination

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

15 posts Page 1 of 1
Hello,

I've been experiencing a strange problem. One of my instruments has been having Chloromethane and Bromomethane contamination in the blanks at around .5ppb-1ppb. It only occurs only when MeOH is present, even the ~2ul present with the ISTD. If I turn off the ISTD there is no response for those two compounds.

I have directly inject the MeOH onto the GC with no contamination (we also run it on 12 other instruments). I have eliminated the autosampler by spiking MeOH into DI and injecting it into the sparge tube.

I have replaced the mount, spargetube, sample pathway lines, sonicated the union and the 6 port value and replaced the traps multiple times.

Any ideas would be appreciated, I am completely stumped.

I am using Tekmar stratum concentrator an Agilent 7890A GC and a 5975c msd.
How do you know that it is those two compounds ?

Peter
Peter Apps
Hello

DReggio wrote:
Hello,

I've been experiencing a strange problem. One of my instruments has been having Chloromethane and Bromomethane contamination in the blanks at around .5ppb-1ppb. It only occurs only when MeOH is present, even the ~2ul present with the ISTD. If I turn off the ISTD there is no response for those two compounds.



So if you to turn off ISTD and run MeOH you see peaks or not?

Regards

Tomasz Kubowicz
I fought a chloromethane contamination problem with the 524 drinking waters I was running once. Waste waters was no problem but all the drinking waters were contaminated. Turned out to be the 1:1 HCl we used for preservative. Apparently a little methanol had gotten into the vial with the acid and the acid had the chloromethane in it. Making a fresh vial of 1:1 HCL fixed the problem.
The past is there to guide us into the future, not to dwell in.
Turned out to be the 1:1 HCl we used for preservative. Apparently a little methanol had gotten into the vial with the acid and the acid had the chloromethane in it. Making a fresh vial of 1:1 HCL fixed the problem.

It turns up in a voa of DI water spiked with 25ul of water (for 2ul per 5ml) but I should look into how the MeOH could be turning into chloromethane.

So if you to turn off ISTD and run MeOH you see peaks or not?

Thanks Tom. Yes, I see the peaks with the ISTD off and MeOH spiked into a VOA vial at the above concentration. It does not sow up if ISTD is off and just DI water is run.

How do you know that it is those two compounds

Hi Peter, the retention times, mass spectra match up and the primary and secondary ions match up. These are compounds we calibrate for (forgot to mention I am running 8260).
DReggio wrote:
How do you know that it is those two compounds

Hi Peter, the retention times, mass spectra match up and the primary and secondary ions match up. These are compounds we calibrate for (forgot to mention I am running 8260).


Less of a mystery if you are using these two compounds in the lab - something has been contaminated somehow. Finding out what is a systematic process of eliminating and substituting all reagents, solvents, glassware etc until they go away. It is tedious like hell, but only really "interesting" if you have multiple sources of contamination that single substitutions will not eliminate.

Peter
Peter Apps
Less of a mystery if you are using these two compounds in the lab - something has been contaminated somehow


Thanks Peter,

It would be odd for these two compounds to contaminate from our standards, as they are some of the lightest and most volatile.

It is not in the MeOH, since the compounds do not show up in direct injections or on other instruments.

It does not show up when MeOH is not present so is is an interaction between MeOH and something in the concentrator. I will try replacing some more parts.
DReggio wrote:
Less of a mystery if you are using these two compounds in the lab - something has been contaminated somehow


Thanks Peter,

It would be odd for these two compounds to contaminate from our standards, as they are some of the lightest and most volatile.

It is not in the MeOH, since the compounds do not show up in direct injections or on other instruments.

It does not show up when MeOH is not present so is is an interaction between MeOH and something in the concentrator. I will try replacing some more parts.


Light and volatile things float around in the air until they find a surface to stick to.

Peter
Peter Apps
Any resolution on this DReggio? We are experiencing almost word for word as you have described. Running 8260 on an agilent 6890/5973, Tekmar 3100 running a vocarb 3000 trap and an archon as. Have 8 other systems in the same room running the same configuration and they don't have the trouble. Our's is primarily Bromomethane formation with the presence of MeOH. It's not present with pure DI but add even a small quantity of MeOH in the voa and we are creating bromomethane above MDL levels. Curious if you can recall any resolution on the matter.
cat4lyst wrote:
Any resolution on this DReggio? We are experiencing almost word for word as you have described. Running 8260 on an agilent 6890/5973, Tekmar 3100 running a vocarb 3000 trap and an archon as. Have 8 other systems in the same room running the same configuration and they don't have the trouble. Our's is primarily Bromomethane formation with the presence of MeOH. It's not present with pure DI but add even a small quantity of MeOH in the voa and we are creating bromomethane above MDL levels. Curious if you can recall any resolution on the matter.
I have the same system except a Tekmar 3000. When this happens for me, its because of active sites in the sample pathway. It also gets worse if using hydrogen as a carrier. What you are seeing are breakdown products from some of the other chlor bromo substituted compounds.
Thanks for the response. This makes sense. We have re-plumbed the tekmar with exception to the bottom of trap heated assembly. So I was starting to wonder if anything else is contributing, like maybe thermal decomp at some hot spot in the system. The phenomenon is noted EPA 5030C purge and trap procedures in section 6.2.5.5.2. But they are only considering the trap, which has been changed several times already. I may need to expand my search to the archon flow paths. Considering your suggestion, I will likely continue down the active site path.
I clean by injecting P&T methanol through the transfer path (except trap) while warm ~50C. Make sure you follow up with 2-3 rinses with DIWater to get rid of the methanol. Leaving the methanol in seems to create active sites when it is heated back up to dryness. Hook up the path to UHP nitrogen or Ar or He but N2 cheapest) and dry it out, not exceeding 20psi. You don't want to damage any seals.

I always run a couple of BFB blanks after doing this to get the system back in moisture equilibrium before trying a CC or a calibration.
I should add, that I run my Archon entirely in soil mode because using the built in internal standards addition does not seem to give stable IS responses over the course of a run. So, I do all my prep off line and purge them right from the vials in soil mode.

So, pathways I clean are from the archon to the Tekmar and then also the transfer line to the 6890. For the transfer line, I push the methanol and water through the carrier line and valve then back out through the transfer line. Then I hook up inert gas to dry the lines out. For the Archon transfer line, I push the methanol and then water from the Archon through the valve and water management etc and out through the top of the trap fitting (with the trap disconnected of course).
So, interestingly we run our systems the same way and have done so for some time. In our case IS addition is not the primary reason for this; decreased carryover from the fresh sparge vessel (VOA) every run is the big advantage to this setup in my opinion.

Thanks for your tips, although I am very familiar with your methodology as we do basically the same thing.

Out of interest, you didn't mention the archon upper soil valve and what we call the U line that connects the sparge needle with the valve. I find they also need to be addressed. Usually disassembly of the valve then sonication in MeOH and I will typically just replace the U line when servicing. Curious if your up to the same things.
cat4lyst wrote:
So, interestingly we run our systems the same way and have done so for some time. In our case IS addition is not the primary reason for this; decreased carryover from the fresh sparge vessel (VOA) every run is the big advantage to this setup in my opinion.

Thanks for your tips, although I am very familiar with your methodology as we do basically the same thing.

Out of interest, you didn't mention the archon upper soil valve and what we call the U line that connects the sparge needle with the valve. I find they also need to be addressed. Usually disassembly of the valve then sonication in MeOH and I will typically just replace the U line when servicing. Curious if your up to the same things.
Copy that, on the decreased carryover.
I do take out the soil valve when I do this and I push methanol and then water through all the parts of that assembly after sonicating the needle. I re-use all the parts, not having replacements to hand. Most of the time if I need to sonicate the needle its because fine sand has clogged it and reduced flow.

I also leak detector check the gas fittings and the source gas filters in the Archon. I was having near zero flow and found they were nearly plugged. I swapped in a union and am looking around for an economical alternative filter to swap in there.
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