1,4 dioxane carry-over problem

[cmoral]

Hi,

We are using a purge&trap system: HP5890 series II GC hooked up to a Tekmar 3000 concentrator and a 2016 and 2032 autosamplers for the analysis of VOCs in groundwater. We are analyzing for 20 compounds, two of which are THF and 1,4 dioxane. We use NaCL to enhance the purging of 1,4 dioxane at 50 oC. Over time, we have noticed that our water blanks contain small amounts of 1,4 dioxane and we have been able to flush the system with success so that no 1,4 dioxane shows up in our system. But lately, we can't seem to get rid of it and the same is true for THF. We have tried everything from baking the column to changing the trap to cleaning out all of the purge lines with water but we aren't having any success. Does anybody out there have any experience with this problem and, if so, could you suggest a solution.

Thanks.

[Don Shelly]

I've seen this before. Heated purge & trap is notorious for gunking up a concentrator. Start by putting your sparge vessel in a muffle furnace and baking out a 400 C to remove all organics. Give it a good wash. Then you need to work your way through the concentrator until you get to the trap and clean everything. Use methanol for cleaning.

I may be biased, but I prefer SPE for 1,4-dioxane. Less down time.

[cmoral]

Hi Don,

Thanks for replying to my query. We haven't tried just pressing the run button on the GC to check if it is a GC problem but I am pretty sure it isn't. I believe it is either the concentrator or the autosamplers that are contaminated. Do you believe it more likely that it is the concentrator rather than the autosamplers? Our next steps will be to try to clean out everything with methanol but may focus primarily on the concentrator.

As for the SPE, we are kind of stuck with using our purge & trap and it did work well until this problem arised.

[Don Shelly]

I doubt it's the autosampler. The heated purge forces all sorts of gunk into the concentrator. It's that gunk that the analyte gets hung up on. I always like to keep my sparge clean also.

Don

[cmoral]

Thanks Don. We will definitely concentrate on the concentrator and see how things work out.
Will let you know.

[chromatographer]

How do you do the SPE analysis of 1,4-dioxane? Is it SPE clean-up followed by purge and trap?

[Don Shelly]

Follow EPA method 521. It is an extraction using activated carbon.

[Steve Reimer]

The extraction method eliminates the water which creates no end of problems, as you are finding out.
I haven't used a Tekmar concentrator but my guess is that you are collecting salt water in your water management system on the concentrator.

[cmoral]

I believe we are collecting salt water in the concentrator but not sure the best way of removing it. We have been flushing everything as much as possible.

One other problem that arose at the same time we started having the 1,4 dioxane problem - all of a sudden we lost our chlorobenzene, mp-, and o-xylene peaks at our lowest standard. Everything else appeared to be comparable, i.e. all the peaks eluting before these three compounds came out at the normal retention time and with comparable area counts. Although this might be coincidental, all the problems appeared to start immediately after we had a major power outage - while the GC was in the middle of a run.

Anybody have any idea what could make this happen all of a sudden?

[cmoral]

We are still having problems with our 1,4 dioxane carry-over and it definitely seems to have occurred after our run was interrupted because of a power failure. Does anybody know what kind of mechanism would occur that would allow the salt water, which we are using for 1,4 dioxane analysis to become trapped in the concentrator or autosamplers when this happens.

Also, at the time the xylenes disappeared, the technician had replaced an old guard column at the head of the volatiles column and it was immediately after that that our xylenes at low levels disappeared. Does anybody have any idea as to why that could have occurred? The old guard column was replaced by an unused one that had been sitting around for several years.

Any ideas would help.

[Don Shelly]

Have you tried replacing the trap?

[cmoral]

Hi,

Yes, we have replaced the trap. Am wondering now if it is a leak in the junction between the analytical column and the guard column for the xylenes problem. We are looking into that. Still working on the 1,4 dioxane carry-over problem.

[cmoral]

Hi all,

For anybody interested in whether we resolved this problem, the answer is sort of. We have spent a lot of time cleaning everything out with methanol and heat and although these have reduced the problem somewhat, these two things themselves did not solve the problem.

It appears with time that the problem is slowly getting better after running many water blanks. So, still not absolutely sure we have gotten rid of all the contamination but one other thing we did was to forego using the salt and that has helped to reduce the contamination without really sacrificing our detection limits. The limit now is 15 ppb, which for our purposes, is fine.

So thanks to all for your help and suggestions.