Analyzing small volume of mixed waste DNAPL for PAHs

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

8 posts Page 1 of 1
Hello,

We have a small volume of a mixed waste DNAPL from an environmental investigation. A volatile analysis reported:

221,000 mg/l trichloroethene
3,090 mg/l toluene
582 mg/l tetrachloroethene
352 mg/l methylcyclohexane
and 12 other VOCs less than 100 mg/l

We believe there are PAHs in the mixture but we haven't had any analysis done. With a small volume of available sample (less than 2oz), how would you go about requesting analysis by a lab?

Thanks in advance,
Tom
Just ask the lab what they can do with your sample. If that is less sample than what they're used to, the analysis will probably be reported at a higher limit than usual (they dilute it to the routine volume).
Looks like parts washing solvent waste. I've seen lots of those. They will typically be designated as a chlorinated waste. Depending on what else is in it it may still flash. Of course I'm assuming that the analysis is for waste characterization.

PAH analysis will just be dilute/cleanup and shoot. The amount is plenty for what the lab will need. But with that much TCE/PERC, does it matter how much benzo(a)pyrene is in it? Any lab request should include what target level you would need to see.
Thanks for the input.

The reason we want to know the PAHs is more for our own interest. We investigated the site using an innovative tool that emits UV light to fluoresce PAHs (if present) as it is pushed/hammered into the subsurface. A down-hole camera detects and analyzes the fluorescence. Chlorinated solvents alone will not fluoresce neither will any of the VOCs that were detected. This DNAPL does fluoresce so we just want to know the PAHs present.
You may have a better result if the lab you choose does the PAH analysis by HPLC fluorescence. They can get low detection limits on the compounds that fluoresce well.
With such high levels and if it contains a lot of other cyclic organic compounds HPLC fluorescence may have too much interference to obtain super low detection limits. We have trouble all the time with such dirty samples on the HPLC. GC/MS SIM would probably cut through the crud if there is interference of that type.

Sample prep would most likely be as a Waste Dilution where you take 0.1g and dilute to 10ml in DCM for GC/MS or ACN for HPLC.
The past is there to guide us into the future, not to dwell in.
Heavy hydrocarbon background can make SIM a problem too. Some sort of cleanup is warranted. Even just a simple silica gel cartridge cleanup could make a big difference.
Yes, silica gel was what we used when we did a project for PAH in air samples on XAD cartridges in an area near coal mines/refineries. It takes a black extract and makes it quite clear.
The past is there to guide us into the future, not to dwell in.
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