Dejan,

Answer to your question is not simple since the question is not well specified. I do not know what you mean by linear external calibration. 

Briefly,  PAHs exist in the air in gaseous and particulate  phases. This phase distributions is temperature dependent. Particulate PAHs concentration depends also aerosol particle diameter. Finally, each PAH has its own vapor pressure which determines gaseous/particulate equilibrium having on mind aerosol particle diameter. So, you have to reflect those facts in your question and than you may obtain good answer.

Jan

Dear Dejan,

I agree with what Jan Hovorka wrote to you. I attached two papers by us for your references, in which there are relative estimations for gas and particle phase PAHs concentration.

Best,

Bin

Okay. What I am doing is collecting PAHs on PM10 filter. At the end of the sample prep I have 1 ml extract. I inject in GC-MS and get some value (signal). I trend the line from mine external calibration curve and end up with (X ng/ul concentration). I divide this buy air volume that has been sampled and multiply by 1000 to get ul to ml. 

Because I cannot find in any literature formula for calculating concentration (ng/m3) (all formulas are associated with internal calibration). Thats why I want to double check if I am doing it correctly.

Hope this makes you more clear.

And thank you for help

You have to account for your injection volume, say 0.5 µl. The mass in ng in the injected liquid is then: X multiplied by 0.5. Convert this to your 1 ml extract (here multiplication by 2000), This is the mass you must correct if necessary for part of your filter extracted, and finally divide this by your sample air volume and correct for dimensions.

Hi Dejan,

I understand your question, but let me know if I am wrong.

I use an external calibration using ng/mL concentrations and generate my calibration curve either in ng/ml or in ug in my injection volume (usually 20uL). To quantify the amount of PAH on my sample extract I measure the exact volume of the extract,  and inject the same volume as for the e.s. From the amount obtained using my calibration and recalculate the total PAH amount in my extraction. As I know exactly how many m3 I extracted (whole filter,  half a filter) I can finally make the correction.

Let me know if you this answers your question. If not you can directly send me an e-mail and we can go in more detail.