Matrix contamination of PAH analysis

[wrighty]

Hi all,

I am currently working on a method for PAH analysis of marine oil to be analysed by GC/MS.

Having searched through previous topics i can see that this field has arisen before with different techniques being proffered.

I am currently using the following method:

-Dissolve oil in hexane and mix with conc sulphuric acid
-Centrifuge contents and remove upper layer
-Run upper layer through supaleco dioxin column
-Concentrate sample down to almost dryness
-Re-suspend contents with 100ul toluene

However, i am experiencing poor recovery (<50%) and there is still quite a lot of noise on my traces from the oil matrix not being removed completely.

If anybody has any experience with this subject i would be grealty of any advice.

Thanks

Steve

[AICMM]

wrighty,

I have never done the acid cleanup step on PAH's so I cannot comment on that. However, I would recommend you divide the problem. Spike you hexane with one deuterated PAH before acid and spike it with another deuterated PAH after the acid but before the Dioxin column. Look at the recoveries of each deuterated component to identify source of the problem. I would also add some toluene before blowdown (perhaps 50 uL.)

Have you thought about GPC cleanup?

Best regards.

[wrighty]

Is the general idea of adding the toluene to act as a barrier from completely blowing the sample dry? thats a good idea

I have considered using LC to analyse the sample but the majority of applications use acetonitrile and considering the cost of purchasing the stuff (i'm talking about regular HPLC grade) is phenominal giving the current stocking. I am unsure about how to use GPC to clean up the sample

I have entertained the idea of using Supercritical Chromatography to collect fractions but this field is new to me and my colleagues- although we have an instrument lying around upstairs somewhere.

Thanks for your suggestions

Steve

[AICMM]

Wrighty,

Yes, the toluene is to retain components, not allow them to blow dry. GPC is a solvent intensive method but not subject to some of the chemical issues that silica gel or florisil cleanup sometimes encounters. There is an EPA method that discusses this process (3640 I believe.) Can be readily set up in house if you have an appropriate solvent pump. If you get serious about setting it up, ping me offline and I can provide more info....

Having said that, if I were in your shoes, I would not give up yet on the method you are using, rather I would try to figure out where I am losing the PAH's.

Best regards.