Spectroscopy Laboratory Quinine in Tonic Water with Fluorescence
Analysis of Quinine in Tonic Water using Fluorescence
Introduction:
Fluorescence is, in a way, the opposite of absorption. Rather than recording the light absorbed by a species, or the light necessary to excite its electrons, we measure the light emitted after the species has been excited and returns to its ground electrical state. Two spectra are produced: emission and excitation. Excitation is similar to absorption, where emission records the intensity of the radiation emitted by the species as it relates to wavelength. Fluorescence is highly sensitive method and can be used in many industries, including food analysis, pharmacy, and natural products. In order to fluoresce, molecules must be rigid, and unable to rotate so that the energy cannot be dissipated by any mechanism except light emission. The orbitals of a species must also not interact with each other so that there is no exchange of energy. There must also be a low concentration of paramagnetic species so that the signal cannot be quenched. The mathematical law used for fluorescence for relatively low absorbing species that can be represented in a linear fashion is as follows: I_F=[ϕ_F I_0 kabC] [1]
Where: I_F=Total Flourescence Intensity ϕ_F=Quantum Efficiency
I_0=Incident Light Intensity a=absorptivity coefficient b=path length
C=Concentration
k=instrumental parameter accounting for multiple directions of flourescence In this experiment, we used fluorescence spectrophotometry to determine the quinine concentration in Tonic Water. We did this by first preparing a blank and a set of standards to create a calibration curve and then used that calibration curve to determine the concentration of a tonic water sample.
Experimental Procedure: The materials required for this experiment were a 0.5M solution of Nitric Acid, 10 ppm standard of quinine sulfate, distilled water, Tonic Water, and 1M solution of Sulfuric Acid. The equipment required was a 500 mL volumetric flask, a
Introduction:
Fluorescence is, in a way, the opposite of absorption. Rather than recording the light absorbed by a species, or the light necessary to excite its electrons, we measure the light emitted after the species has been excited and returns to its ground electrical state. Two spectra are produced: emission and excitation. Excitation is similar to absorption, where emission records the intensity of the radiation emitted by the species as it relates to wavelength. Fluorescence is highly sensitive method and can be used in many industries, including food analysis, pharmacy, and natural products. In order to fluoresce, molecules must be rigid, and unable to rotate so that the energy cannot be dissipated by any mechanism except light emission. The orbitals of a species must also not interact with each other so that there is no exchange of energy. There must also be a low concentration of paramagnetic species so that the signal cannot be quenched. The mathematical law used for fluorescence for relatively low absorbing species that can be represented in a linear fashion is as follows: I_F=[ϕ_F I_0 kabC] [1]
Where: I_F=Total Flourescence Intensity ϕ_F=Quantum Efficiency
I_0=Incident Light Intensity a=absorptivity coefficient b=path length
C=Concentration
k=instrumental parameter accounting for multiple directions of flourescence In this experiment, we used fluorescence spectrophotometry to determine the quinine concentration in Tonic Water. We did this by first preparing a blank and a set of standards to create a calibration curve and then used that calibration curve to determine the concentration of a tonic water sample.
Experimental Procedure: The materials required for this experiment were a 0.5M solution of Nitric Acid, 10 ppm standard of quinine sulfate, distilled water, Tonic Water, and 1M solution of Sulfuric Acid. The equipment required was a 500 mL volumetric flask, a
References: [1]Andreescu, D. CHEM 223 Spectroscopy Laboratory Fall 2013 Edition; 2013; pp 77-82 [2] Swain, J. The Boston Globe, 2010. http://www.boston.com/business/articles/2010/03/01/ what_is_tonic_water/ Accessed 10/29/2013