Public Lab Research note

Replicating the Grading of oils with UV Fluorescence on other cameras pt 1

by mathew | September 22, 2014 03:20 22 Sep 03:20 | #11168 | #11168

What I want to do

replicate the results of my previous note using different other cameras. I want to know if the shift in the location of a spectra's peak from blue-green as a measure a series of heavy-to-light oils is reproducible. I took the spectra in the previous research note with a Syba camera that shipped in our first and second Desktop spectrometry kits, Here I compare to the Sanm camera found in the current Desktop Spectrometer and the infragram Webcam.

I want to see a replication of this pattern, where heavier = bluer. preferably at the same location.

  • 5W-30 has a peak at 444nm
  • 20W-50 at 436-8nm
  • 80W-90 at 432-435nm

My attempt and results

I started measuring the styrene cuvettes I'd used in my previous trials, but some of them were melting (yes, melting) from contact with the oils and especially the diesel.

The Infragram Webcam has been deconstructed, and its blue filter removed, and the surface of the CCD cleaned off with denatured alcohol. Its focal length is set to 9." It is quite a bit more sensitive than the syba cam, and produces bright spectra. That becomes an issue. It could perhaps be attenuated with an optically-printed slit. It seemed like I got a lot of "blown out" spectra.

I tried some spectra through a polarized grating to attenuate it. it seemed to match the dimmer spectra taken off-center from the fluorescing oil.

just looking at and trusting (becuase they look nice) the lower peaks, I'm not able to grade the oil:

I'm not really seeing a clear difference in the peaks between diesel and crude either:

Sanm cameras

the crude peaks, even the "clearest" looking ones between syba, sanm, and infragram cameras are all different.

comparing crude to diesel on each leads to differing conclusions. The infragram camera and sanm cam both have a bluer peak fro diesel than crude, the opposite of what I'd expect, and neither is in the same place.

Questions and next steps

testing all the other cameras I have here built into spectrometers.

Why I'm interested


this camera has these rounded diesel and oil curves. ND crude is decidedly greener than diesel in these spectra.

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It sounds like the cuvettes absorb some oils (not quite the same as melting, but bad none the less). Plastic cuvettes are made for use with aqueous solutions. My guess is that the gel caps did this as well, and probably to a greater extent.
The cure for that is to go with glass. Here is a glass cuvette for $16 with shipping. You could try working with a more polar solvent. Perhaps isopropanol (rubbing alcohol). I dont know if the plastic would stand up to that solvent but it might be worth a shot. If you do try it, you should know that fluorescence can be sensitive to changes in solvent polarity. Good luck. Jack

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Mathew's notes on how overexposure/clipping can mess up curve shape are very important here and underscore @stoft's encouragement that we screen for, and do our best to avoid, clipping. Just looking at this set:


There, only the first one -- "IRCAM North Dakota Crude" seems to be clipping. It is quite different in shape, too. Clipping shown when you use "RGB mode" while looking the spectrum alone:


Perhaps we should display in-graph warnings anytime there's clipping - without looking at RGB, it's easy to miss when it happens.

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