Spectrometer

Purpose

Chemists use expensive tools called spectrometers (there are several kinds) to analyze unknown solid or liquid samples. We are working on a cheap version which we hope to use to identify oil contamination in water and soil, as well as a range of other possible toxins.

Spectrometers can also be used to identify species of plants or crop diseases, assess plumes from smokestacks, and have many other applications.

What's spectrometry?

What we often perceive as a single color actually consists of multiple blended colors- just as green paint can be made from mixing yellow and blue paint. A spectrometer is a device that splits light into the various colors it is composed of, which we otherwise cannot distinguish with the naked eye.

The particle upshot of this is that by viewing a substance through a spectrometer, one can distinguish the exact mixture of colors, which correspond to specific wavelengths of light, that make up the perceived color of the sample.

The Tool:

The PLOTS spectrometer is a DIY tool made from simple materials: cardboard, tape, a CD, and a digital camera. The CD is the key component: the tightly packed grooves in the CD act as a diffraction grating. When light enters a diffraction grating, the different wavelengths of light are bent to different degrees, proportionally to their wavelength, splitting the light into its component wavelengths.

There are several versions of the spectrometer:

• Tube spectrometer
• Webcam-based "Video spectrometer" - currently the latest version

The Application:

It is the ultimate goal for this research to use the PLOTS spectrometer to identify contaminants stemming from fossil fuels in water and air samples. With these capabilities, the spectrometer could be used to identify pollution due to oil spills (Gulf Coast), industrial activity (Gowanus Canal, NY), or natural gas extraction. One group of toxins common to fossil fuel contamination are PAHs, polycyclic aromatic hydrocarbons, which are generally carcinogenic. The PLOTS spectrometer aims to be cheap, easy to manufacture, and easy to use, which could empower people concerned about fossil fuel contamination by giving them the tools to test for pollution, and raise awareness about the problem.

The spectrometer has also been the subject of a public workshop by Jeff Warren and Nadya Peek at Escuelab in collaboration with FabLabLima in Lima, Peru:

http://publiclaboratory.org/report/diy-spectrometry-workshop-lima-peru

Online spectral analysis

Along with the physical tool itself, the PLOTS team has also developed an online application which allows anyone to upload a spectrum photographed with a digital camera to the website, and use the online tool to analyze the intensity of the spectrum. The intensity of the spectrum at each wavelength adds a second dimension to the data, allowing for more accurate comparisons to known spectrums.

Another tutorial:

Resources, Downloads, FAQ

Access the online tool (still a prototype) at: http://spectrometer.publiclaboratory.org

You can find instructions for making your own spectrometer by Alex McCarthy here:

Make a Spectrometer

And another prepared by the PLOTS team for our workshop at the Whitney Museum, here:

plots-spectrometer-guide-small.pdf

Finally, a FAQ with some insights about actually using your spectrometer can be found here:

Spectrometer FAQ