UV-Vis Spectroscopy (Exam 3) Flashcards
UV-Vis is useful for { } measurements when the type of compound to be analyzed is known.
Quantitative
UV-Vis is a fast, simple, and inexpensive method for determining the { } of an analyte in solution.
Concentration
What are the 3 sub-domains of the UV-Vis region?
Near UV, visible, and very near IR
Why do we perceive a red apple as red?
It’s complementary color light, green, is absorbed while the red light reflects back to our eyes
Lambert-Beer’s Law establishes a { } relationship between absorbance and concentration.
Linear
What are the 4 causes of non-linearity in a Lambert-Beer plot?
1) High concentration
2) Scattering/fluoresence/phosphorescence
3) Refractive index change
4) Nonmonochromatic radiation
How do you minimize non-linearity/deviation in a Lambert-Beer plot?
Use lambda max
What are the 4 changes/shifts that UV-Vis spectra are sensitive to?
1) Solvent
2) pH
3) Conjugation (molecular)
4) Temperature
What two lamps are used for UV-Vis spectroscopy? Name their associated region too.
1) Deuterium (UV)
2) Tungsten (Vis)
A shift to a longer wavelength commonly called red shift.
What is bathochromic?
A shift to a shorter wavelength commonly called blue shift.
What is hypsochromic?
Increase in molar absorptivity.
What is hyperchromic?
Decrease in molar absorptivity.
What is hypochromic?
How is the choice in solvent affect UV-Vis spectroscopy?
Solvents can cause changes in peak intensity and lambda max
What is the working principle behind solvent cutoff?
Choice of solvent should have a wavelength below which the solvent absorbs all light i.e. a sample that absorbs light at 350 nm should be paired with a solvent that absorbs light about 300 nm and below
