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I have a sample (for the purpose of this question let's call this Sample A) consisting of oil (edible olive oil) mixed with a contaminant (Contaminant B) from the Polycyclic Aromatic Hydrocarbons family.

I have tested pure forms of Contaminant B with gold nanoparticles and I am able to see great signals. (Surface Enhanced Raman Spectroscopy) 

When I try to perform SERS on Sample A I notice that the peaks are suddenly gone. I suspect the following:

  1. The signals from the PAH is being shadowed by the fluorescence of the oil 
  2. The signals from the PAH is being absorbed by the oil molecules, leaving no observable peaks 
  3. The oil molecules is preventing the PAH molecules from being in close physical proximity to the gold nanoparticles for SERS's enhancement 

Question ONE: Which of these is true?

Question TWO: How can I solve this problem? I can only think of: 

  1. Photobleaching (not really practical for the purpose of my paper)
  2. Chromatography on Sample A (tried Acetone and Methanol but to no avail)
  3. Adding an agent that could eliminate fluorescence from the oil molecules (I have no idea what could achieve this)
  4. Adding an agent to digest or destroy the oil in Sample A leaving just the PAH in the remaining solution (again, no idea what this could be)
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  • $\begingroup$ To answer, it would be helpful to have more technical details about your measurements. What wavelength of (laser?) light are you using for your Raman detection? When you say "the peaks are gone", is it because the baseline has gone up? Or because the baseline is the same and the signal is lower? $\endgroup$ – Curt F. Dec 28 '15 at 16:07
  • $\begingroup$ Also, what concentration of Contaminant B did you use in your studies of the "pure form" of B? 100%? What concentration range do you expect for B in Sample A? Parts per thousand? Parts per billion? Does that expected range overlap with what you used in your "pure form" studies? $\endgroup$ – Curt F. Dec 28 '15 at 16:08
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    $\begingroup$ @CurtF. 785nm laser. Peaks are gone = peaks are not there anymore but the baseline is not higher. In my pure form of study of Contaminant B I was able to pick up signals all the way from solid to 1 ppm. Sample A contains 100 ppm of Contaminant B $\endgroup$ – Sparrowcide Dec 28 '15 at 19:47
  • $\begingroup$ When you made solutions of pure Contaminant B to study, what solvent did you use? $\endgroup$ – Curt F. Dec 29 '15 at 5:11
  • $\begingroup$ @CurtF. We followed this paper: scribd.com/doc/294198642/… To answer your question: Methanol $\endgroup$ – Sparrowcide Dec 29 '15 at 8:22

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