UV-VIS Spectroscopy Flashcards
What is UV-Vis spectroscopy?
- Ultraviolet-visible spectroscopy, involves the absorption of UV/visible light by a molecule causing the promotion of an electron from the ground electronic state to an excited electronic state which have a wavelength between 190 & 800 nm
- It is the analysis of UV/VIS absorbance scans of amino acids
What does absorption spectroscopy show?
1) provides information about presence and absence of unsaturated functional groups
2) determines concentration (especially in chromatography)
3) provides structure proof, essential for further studies
4) NMR, MS not good for purity
What is meant by absorption?
The transfer from a lower level to a higher level with the transfer of energy from the radiation field to an absorber, atom, molecule or a solid
What is meant by emission?
A transition from a higher level to a lower level via the transfer of energy rom the emitter to the radiation field, if no radiation is emitted the transition from higher energy to lower energy levels is called non-radiative decay
What are the two main properties of an absorbance peak?
1) absorption wavelength (X-axis)
2) absorption intensity (Y-axis)
What is beer-lambert law?
Sometimes we want to know how quickly or slowly a chemical reaction will occur, but what is the reaction doesn’t use the product in a different phase than the solution? Here comes spectroscopy, the study of how light interacts with matter, all molecules absorbs and emits light differently based on the covalent bonds in the molecule. If the product and reactant interacts with light differently enough that there is a color change, we can monitor this process using spectrophotometer which can measure changing concentration giving us data in the form of an absorption spectrum which displays how much light through a band of frequencies is able to pass through a sample to reach the detector, where there is peaks in the graph it means that not as much light of that wavelength is getting to the detector which means that it is being absorbed by the sample, if we collect this data continuously over the duration of a chemical reaction we can gather data about how rapidly the absorption changes and thus how the concentration of a specific substance changes over time, in order to use this we use the beers-law (A “absorbance”=ebc) (e= molar-absorptivity “how well a compound absorbs a given wavelength of light”) (b= path length “distance the light must travel through the sample”) (c= concentration of the sample) which relates the amount of material in a sample to the absorption of the light passing through it. Absorbance measures the intensity of light as it enters the sample (I0) and the intensity as it leaves the sample striking a detector (I). A= log(I0/i) = log(io/i) = ebc
A compound has a molar absorptivity of 40.9cm^-1M6-1 at 203nm. If a 1cm cuvette is used, and the absorbance found to be 0.111, what is the concentration of the sample?
A=ebc
1) 0.111 = 40.9 * 1 * c
2) 0.111/40.9 * 1= c
3) c = 2.71 * 10^-3 M
