Caren Sullivan–November 18th, 2015

As the term draws to an end, of course it’s difficult to find time in the lab. However, I–pardon the expression as a vegetarian–killed two birds with one stone by doing my final project for Advanced Inorganic Chemistry on iron gall ink! Thanks to a paper I found on ACS (http://pubs.acs.org/doi/pdf/10.1021/ja5027612), I now have reference Raman spectra with a 785 nm wavelength laser of gallic acid powder and iron gall ink in solution that was purchased from the Art Institute in Chicago. So I gathered my own Raman spectra at both 532 nm and 785 nm excitation wavelengths of my iron gall ink solution so that I can compare to theirs. Furthermore, it would be really cool if we could utilize the 532 nm laser more than we have in the past, and through Shifted-Subtracted Raman spectroscopy (SSRS) that may be possible! The basic methodology behind SSRS is to collect three spectra of the same sample at slightly shifted spectrometer gratings. So, all three spectra would be collected using the 532 nm laser and at a particular grating (i.e. 600T). The first of the three spectra is collected at normal parameters. Then, the spectrometer is shifted manually by approximately 21 inverse centimeters and a second spectrum is collected. Finally, a third spectrum is collected by shifting the spectrometer 43 inverse centimeters from the original position. The first spectra is then subtracted from both the second and the third, respectively. Then, the process is repeated several times and the spectra are averaged. The spectra are then fitted using double Lorentzian functions and a best guess spectrum is produced. Ultimately, this technique subtracts the fluorescence and noise from the spectra by collecting multiple spectra that all contain the same noise. Lastly, my plan for Winter break is to continue making the news inks I’m fermenting and focus on applying to grad schools, while reading up more on this cool SSRS technique!

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