What I want to do
Scott Eustis and I and others have made a number of attempts to get clear fluorescence spectra by shining a green laser through mineral oil which has had small amounts of crude oil dissolved in it. But we've struggled to get enough brightness into a Desktop Spectrometer.
My attempt and results
Today over lunch I was fiddling with a UV laser (~405 nanometers: buy on Amazon here for $8) with Matt Hirsch and we suddenly realized that it produces a much stronger spectrum than green lasers had. This may be because a laser can only create fluorescence at longer (lower energy) wavelengths than its own -- so green lasers could never create blue fluorescence. See the setup in the lead image for how we did it -- it was pretty easy. But PLEASE be careful not to shine this in your eye, and don't look at the laser dot directly as this could be a strong UV laser and could damage your eye even though it's hard to see with the naked eye.
The spectra were remarkably strong:
This is very exciting because it has a pretty good signal to noise ratio, and it's a lot to work with for potentially matching oils.
Questions and next steps
We were also able to measure the spectrum of Bertolli olive oil and an unidentified fuel liquid which is probably paraffin. So one thing we should do is take a lot of spectra of different oils and see if we can reliably distinguish them! If you do this, tag your spectra with "oil" please!
Finally, I created a little black cardboard box with the whole setup taped down inside to streamline the process. It includes space to store your laser pointer and samples, and standardizes the position and orientation of the laser and sample container. It's VERY helpful in doing these sorts of tests, especially for reducing stray light:
Update: Link to sample containers I used: http://www.sciplus.com/p/WHITCAP-BOTTLE_48212
15 Comments
Jeff, nice experiment. Yes, UV is the right choice -- the shorter the wavelength the better. I'm assuming that the UV-light 'reference' was with water and the oil tests were with some small amount added to the water. Right? What is interesting is the dramatic drop in the UV carrier signal. This would make quantitative measurements difficult. At least there appears to be sufficient signal outside of the UV carrier signature. -Dave
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I would love to be able to characterize oils, olive oil in particular. Two areas of characterization: Adulteration and Quality.
A very high percentage of Extra Virgin Olive Oils (60% in a UC Davis study 4 years ago) are blended with either oils not from olives or from olive oil that has been extracted using solvents that are still in the oil. That Bertolli you tested probably has those solvents in it. I'd like to see a way for consumers to detect this easily, or at least a techy consumer. Palm oil is a very common blending oil in EVOO.
Another high percentage problem in store purchased EVOO is the oil is not really EVOO. The most common problem is storage failure: Too old, to high or low temperature during storage, or exposure to UV light that destroys the monounsaturated bonds in olive oil. Most of these defects show up as the presence of free fatty acids or in loss of polyphenol levels.
Disclaimer - I produce EVOO, and I try my best to make it the best, so finding a tool that makes it easy to see quality difference would benefit me and others like me.
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