In a spectrometer, white light shines through a sample solution. The solution absorbs certain wavelengths of light. A diffraction grating then spreads the light into its colour spectrum like a prism. Chemists analyze the spectrum to tell them about the properties of the sample.
In Scheeline's device, a single light-emitting diode (LED) powered by a 3-volt battery (as used in key fobs to remotely lock a car) is used as the light source. Diffraction gratings are available from scientific supply companies, as are cuvettes, the small, clear containers to hold the sample solutions. The mobile (cell) phone is used to take a photo of the spectrum obtained. Then the JPEG photo is analyzed using a software program freely accessible online:
- Build a spectrometer as per the instructions given in here : http://www.asdlib.org/onlineArticles/elabware/Scheeline_Kelly_Spectrophotometer/HSFiles/3.html
- Follow the instructions in the preparation of a solutions of different concentrations, including a blank.
- Record each spectrum produced by taking a photo of it.
- Upload the photos into the programme which you should download using the link above.
- Data will be available as an exported csv file for excel.
- Plot absorbance versus concentration.
- Obtain a solution of unknown concentration.
- Use the plot above to determine the concentration of this solution.