In this lab work we quantified quinine in tonic water using fluorimetric detection. We also observed the fluorescence of other products: curry, detergent, eosin dye, eggs and two cardiovascular drugs.
Curry and detergent were solids and we made a solution in methanol (volumetric flasks). Eosin dye is liquid, but we also made a solution in order to dilute it. Then we put a drop of these solutions in non-fluorescent paper. Using a UV lamp that can work at two wavelengths (254 and 365 nm) we studied the fluorescence. As you can see in the following picture, the results changed depending on the wavelength. Fluorescence is the emission of light that we observe when electrons that have been excited (moved to a higher energy level) return to a lower energetic level. Thus, the excitation wavelength is a critical parameter.
But, why are these products fluorescent? The answer is in some of their compounds: curcumin (see the nice infography at Compound of Interest), whiteners such as stilbens (they compensate for the yellowing of clothes), or eosin itself (a dye used for cell staining).
We also studied the fluorescence of some drugs. This is a very interesting property that can help us to quantify low concentrations of drugs in different matrices such as plasma or urine. As you can see in the picture, amiloride is fluorescence at both wavelengths. Indeed, this molecule has a maximum absorption that matches with the 365 nm wavelength. Propranolol fluorescence can only be slightly appreciated at 254 nm. Notice that the TLC plate we used to place the drug solutions has a green fluorescence. This is due to the addition of fluorescent substances that help to identify the spots when performing this kind of chromatography.
Finally, and under darker conditions than the ones we had during the lesson, I obtained this picture that shows the red fluorescence of eggs.
Which compound is behind this fluorescence? Surprisingly enough, it is a molecule connected to hemoglobin and chlorophyll... Once again, let me recommend you this web.
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