4. Describe the procedure for preparing a liquid sample lot infrared examination

Question

4. Describe the procedure for preparing a liquid sample lot infrared examination. 5. Although IR spectra of solids are most commonly run as KBr pellets, they are sometimes run as solutions. Even though most organic compounds are more soluble in acetone than they are in tetra chloromethane (CCI4), acetone is almost never used as a solvent in running IR spectra of solids. However, CCL, is very acceptable provided that the solid will dissolve in it. Briefly explain why CCI4 is the preferred solvent.

Explanation / Answer

Ans 4:

To prepare a liquid sample to IR analysis, firstly place a drop of the liquid on the face of a highly polished salt plate (such as NaCl, AgCl or KBr), then place a second plate on top of the first plate so as to spread the liquid in a thin layer between the plates, and clamps the plates together. Finally wipe off the liquid out of the edge of plate. You can mount the sandwich plate onto the sample holder. After finishing your experiment, clean the plates with isopropanol (No water!) and return them to the desiccators.

Ans 5:

Acetone absorbs strongly around 1700 cm^-1, which is an area of interest when analyzing organic molecules. CCl4 is the best, as it the only solvent that won't generate a peak in the important region of the IR graph (4,000-1500 cm-1). All the others would interfere with analysis of important functional groups of the compound that is being studied.

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