Learning Objectives:

1. Determine the benefits of Raman and IR spectroscopies

2. Analyze similar compounds with vibrational spectroscopies

 

Introduction:

There are a variety of analytical instruments used to quantitively measure concentrations of atomic and molecular components in solution. It is typical to analyze atomic species with atomic absorption while molecular species are often analyzed using UV-Vis, HPLC, or GC. When determining the concentration of a molecule in solution by one of these methods there is typically rather significant sample preparation. For example, since UV-Vis utilizes absorbance of light in the visible and ultraviolet range, a complex must be formed that colors the solution in accordance with the molecule of interest. Methods such as HPLC and GC have further issues due to their long run times. All the methods previously listed are also destructive to the original sample. Vibrational spectroscopy such as IR and Raman can be more appropriate for analysis as they are nondestructive and quick. IR spectroscopy has its own issues, however, as water significantly obscures the signal. Raman does not have this issue. In fact, water is nearly invisible in Raman. Recent advancements in Raman spectrometry have made the process of obtaining Raman spectra fast, easy, and non-destructive.

 

In this lab, you will utilize Raman spectroscopy to quickly determine the mole fractions of methanol, ethanol, and water in a solution.