Public Lab Research note

Spectrometry UROP last (for me) update

by Alex-McCarthy | May 30, 2011 14:35 30 May 14:35 | #305 | #305

The semester has ended, and so has my research with the PLOTs spectrometer, which will be picked up this summer by another student. I thought I would post a general outline of what I accomplished this (half) semester, and where I would have gone next.

One of my major goals was to create a new low cost spectrometer that is easier to build, photograph with, and with higher resolution. I am happy with the resulting product, "spectrometer 3.0" as it uses only card-stock, tape, and a CD, while providing a clean, sharp spectrum that can be easily photographed, in a repeatable fashion. My main testing ground for the quality of the spectra photographed was the spectrum of a fluorescent light, which I could compare to that of professionally taken spectrum.

In my research, I found that detecting PAHs using spectrometry, there were two methods. I could try to analyze the spectrum of fluorescing PAHs, which adsorb UV and fluoresce in the visible of near UV range. This proved difficult as the fluorescence PAHs, especially in the diluted state they would be tested in, is very weak. The other option was to photograph the adsorption spectrum of the PAHs in the UV range. With a modified digital camera that could photograph UV light (I am unsure how far into the UV this camera could sense) it was theoretically possible to photograph UV spectrum. My initial problem was that polycarbonate, from which the CD diffraction gratings are made, adsorbs UV significantly. Using a DVD, I created a new spectrometer with a reflective grating that would not filter out UV, during my last week of research.

Next I would try to use this new spectrometer to photograph the UV adsorption of various petroleum compounds, and also samples of gulf coast oil contaminated samples. There may still need to be work done in setting up a standardized testing set up- a way to mount the sample, spectrometer, and light source in a consistent fashion.


Great work, Alex -

I noted on this page that the UV cutoff of glass is supposed to be 350nm, according to my remote sensing textbook. Where are the aborbtion lines you're looking for in the UV range? As your last official act, can you post an image or link?

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