PAH by hexane/acetone microwave/ultrasonic extraction

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

5 posts Page 1 of 1
Is anyone doing PAH in soils using the 1:1 hexane:acetone mixture either with method 3546 (microwave) or 3550c (ultrasonic) methods? I'm thinking about trying it for PAH analysis via method 8270. I'd try to use my 5890/5971 GC-MS and a DB-5ms (19091S-433) 30m x 0.25mm x 0.25um column with helium carrier.

I've never done any of the 8270 analytes but I am starting to send out quite a few samples for PAH and I'm thinking PAH might be a nice subset to get some experience with the method. I want to use the hexane/acetone extraction because I'm trying to keep methylene chloride away from affecting my 8260 methods.
Normally when using this method you exchange into methylene chloride before injection, which takes a bit of doing since it boils so much lower than the other two solvents. I also have found exchanging into ethyl acetate to work very well and it works great for doing solvent effect injections since you can have the oven start at 70C instead of needing a far cooler starting temperature.

PAH compounds are fairly easy to get to work on a 5 phase column, just remember you need an injection temp of around 275C to get them to transfer quickly to the column, lower temps work but you get more tailing in the last eluting peaks.

We are getting ready to try the microwave extractions ourselves, we have done the sonication in the past with good results.
The past is there to guide us into the future, not to dwell in.
Too bad mineral oil would probably elute right in the PAH range. Back when I did pesticides and PCB's in the early 1990's by sep funnel extraction, I used to add a mL of isooctane which contained mineral oil (I think it was maybe 1 mL mineral oil per Liter of isooctane). This worked great for volume reducing the methylene chloride for injection. Even if it went dry, the pesticides and PCB's were still there in the mineral oil residue, and could be picked back up with fresh solvent.
James_Ball wrote:
Normally when using this method you exchange into methylene chloride before injection, which takes a bit of doing since it boils so much lower than the other two solvents. I also have found exchanging into ethyl acetate to work very well and it works great for doing solvent effect injections since you can have the oven start at 70C instead of needing a far cooler starting temperature.

PAH compounds are fairly easy to get to work on a 5 phase column, just remember you need an injection temp of around 275C to get them to transfer quickly to the column, lower temps work but you get more tailing in the last eluting peaks.

We are getting ready to try the microwave extractions ourselves, we have done the sonication in the past with good results.
I can see why exchanging to hexane is a problem since its the acetone/n-hexane azeotrope boils at 49.8C and the vapor is 41% hexane 59% acetone. I'll try and find some ethyl acetate azeotrope data. Sounds like ethyl acetate is not too harmful to have in a volatiles lab.
LALman wrote:
James_Ball wrote:
Normally when using this method you exchange into methylene chloride before injection, which takes a bit of doing since it boils so much lower than the other two solvents. I also have found exchanging into ethyl acetate to work very well and it works great for doing solvent effect injections since you can have the oven start at 70C instead of needing a far cooler starting temperature.

PAH compounds are fairly easy to get to work on a 5 phase column, just remember you need an injection temp of around 275C to get them to transfer quickly to the column, lower temps work but you get more tailing in the last eluting peaks.

We are getting ready to try the microwave extractions ourselves, we have done the sonication in the past with good results.
I can see why exchanging to hexane is a problem since its the acetone/n-hexane azeotrope boils at 49.8C and the vapor is 41% hexane 59% acetone. I'll try and find some ethyl acetate azeotrope data. Sounds like ethyl acetate is not too harmful to have in a volatiles lab.


I think the only time I have to report ethyl acetate is if the client asks for a full appendix 9 list so not often I worry about it. Evaporating in the hood takes care of most of the fumes and the high boiling point of the ethyl acetate makes it easy to exchange. I also like the lower toxicity of the ethyl acetate versus methylene chloride, I just wish more EPA methods would allow it.
The past is there to guide us into the future, not to dwell in.
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