Tetryl analysis in soil

[jackhandy]

How do you deal with the photolysis of tetryl in your analyses? We do fine in the LCS, meet our limits well. However, when doing a 'known' soil pe study, we did not recover the tetryl.

Since the LCS was successful, I'm concerned that the pe sample is being exposed to light or heat prior to getting to extractions. I know that tetryl is gone with in approx 20min of light degradation.

The weird piece is that the water pe study we recovered tetryl just fine.

Too weird. TIA

[Uwe Neue]

How about adsorption to the soil being the problem, rather than degradation?

[bisnettrj2]

If you suspect UV degradation, then all your extracts should be in amber glass containers during extraction and kept in a refrigerator (I believe EPA 8330B say 2-6 Celsius) until analysis.

To Uwe's point - are you getting spiked soil from a manufacturer that you're then extracting, or are you getting an ampoule of spike solution that you're adding to soil? If you're getting a container of spiked soil, is it stored in a refrigerator or freezer until you perform the extraction? Is it in an amber container? And the manufacturer must have recovery limits posted for the PE study - how wide are the limits for Tetryl? Tetryl is a known 'poor performer' according to the NELAC and the DoD, and as such the recovery limits for Tetryl in soil are about 10-150%, with a 'marginal exceedance' lower limit of 0%. So, even if you're not recovering 100%, you probably don't have a problem with you're extraction as long as you're within limits on the other analytes in PE sample. So, are you getting good recoveries for the other analytes in the PE?

Also, just because there's Tetryl in the water PE doesn't mean the manufacturer put Tetryl in the soil PE. So, unless you have been told that you failed the PE by the manufacturer, and that you should have recovered Tetryl, you might be worrying over nothing.

[jackhandy]

It's an interesting concept that you can fail tetryl and still pass the PE. We did fail for tetryl, twice. We did not fail the PE, but we have a bit of a perfectionist in the QA department, so even one failure is too many. Granted, I'm just annoyed enough to want to figure this out.

The PE came in prespiked soil, appropriately refridgerated. We used a LCS in Ottawa sand that recovered well. Amber glassware all around. The only part we need to investigate further is the hand off from receiving to extractions. We're doing a mock run next week.

Thanks for your input. It really helps to have validation of my ideas and clear additional points to consider.

[bisnettrj2]

I've never had problems recovering Tetryl (reasonably - it is a crap analyte) in my normal analysis. Even my worst recovery has been above 30% in soil, and I've never failed a PE for Tetryl. So, I have a few questions...

1. What are you using for your extraction solvent?

2. How are you handling your extract after the extraction is finished?

3. What is the extraction process you are using?

4. How did you do on the other analytes in the PE? Did you recover within the specified control limits?


If I may, a suggestion for your process of evaluation:

1. Obtain two PEs from the same lot (make sure they've been spiked with Tetryl).

2. Obtain different spiking media (Ottawa sand, glass beads, perhaps some sieved, baked soil from around the lab (I'm serious)).

3. Create your own PEs by spiking the different media with a known amount of surrogate and Tetryl, log them in as samples, and give them to your receiving staff.

4. When extraction gets all the weird PE samples, have them surrogate the two PE samples only (since you already surrogated the other ones). Have them spike Tetryl into the second PE at an amount you expect to see in the PE (probably 1 mg/kg?). Then extract all the PEs as normal.

5. Also have your extraction staff add your extraction solvent to an extraction container without any solid media, and then add surrogate and Tetryl in the same amount that was added to the second PE, and extract it along with the other PEs.

6. After extraction, segregate all extracts into two aliquots in identical container types. Take another two of these container types and add your extraction solvent and the same amount of Tetryl and surrogate as added to the extraction container that you had the extraction staff 'extract' without any solid media.

7. Process one of the set of extracts in the way you typically handle and analyze them.

8. For the other set, try to think of a completely different way to prep them for analysis (e.g., if you normally filter extracts, try to just centrifuge them, or vice-versa).

The results should (I think) tell you whether you have an issue with the sample handling, the extraction, or the sample prep. For example, if everything recovers poorly except the two spiked in extraction , then you have a sample handling problem in receiving/extraction. If all your extracts except the one spiked into the solvent-only jar are bad, then perhaps you have a soil adsorption problem. If one analysis prep method causes Tetryl to fail over the other, it may be the way you're handling the samples. And if everyhting fails all over the place, it may be the containers you're storing the extracts in.

Since your LCSs recover well, I think the telling results will be in the PEs you create and give to your receiving staff, and in the PE spiked with Tetryl in extraction. Could give rise to a complete overhaul of how your receiving and extraction staff handle samples, which is troubling in its own right.


I hope I've helped. Good luck with your investigation.