IV. ANALYTICAL TECHNIQUES

7. Ultraviolet/Visible Spectroscopy (UV/VIS)

1. What kind of electrons must a compound have to display UV/Vis activity ?
2. In UV/VIS, why does the absorption spectrum of a molecule appear as a broad band?
3. What is the intensity of absorption in UV/VIS dependent upon?
4. What is the usual source for UV radiation?
5. What is the usual source for visible radiation?
6. What criteria should be considered when choosing a solvent to dissolve your sample in prior to obtaining an ultraviolet absorption spectrum of the solution?
7. What is a chromophore?
8. What is an auxochrome?
9. In addition to auxochromes, what other things can affect the UV absorption of a molecule?
10. Can UV spectrophotometry be used for quantitative analysis?
11. What characterizes a good chromophore?
12. When referring to electromagnetic (EM) radiation, how do frequency and wavelength relate to each other?
13. What is a wavenumber? How does it relate to frequency and wavelength?
14. What is the Beer-Lambert Law?
15. What is є? What units does є use?
16. What is the order of the Beer-Lambert equation and how does this impact on its applicability in quantitative analyses.
17. Why is UV-Vis not considered as discriminating as GC-MS or IR?
18. Traditionally, what is the typical solvent used for UV-Vis in drug analysis? Can other solvents be used? If so, what are the benefits and drawbacks of their use?
19. What scientific law governs UV-Vis as a quantitative technique?
20. What are the benefits of quantitation with UV-Vis, compared to other drug analysis techniques?
21. Can multiple analytes be quantitated in a single sample? What conditions have to be satisfied for this to occur?
22. What materials can the cuvette be made from? What are the most common materials?
23. What’s the difference between a single-beam and a double-beam UV-Vis spectrometer? How does this difference manifest itself on a practical level?
24. How are solid samples prepped for UV-Vis analysis?
25. How are solvent samples prepped for UV-Vis analysis?
26. List some of the common preventive maintenance practices for a UV-Vis spectrometer.
27. What is the most common cause of poor spectra with a UV-Vis spectrometer?
28. List some circumstances in which UV-Vis spectrometry is a superior analysis technique.
29. What are the limitations of UV-Vis spectrometry?
30. Can the UV-Vis spectrum of a pure compound be related to its electronic structure and the chromophores present?
31. Describe the transition of a pi electron from its ground state molecular orbital to its excited state.
32. How does the radiation energy in the form of frequency or wavelength interact with the molecular orbitals states?
33. Describe the components of UV-VIS spectrometer (detector, source, sample introduction) and their limitations.
34. How does a change in solution pH affect the change in the transitions between molecular orbital energy states?
35. What are the strengths of the UV-VIS experiment in drug analysis in differentiating different abused street drugs? What are the limitations?
36. If a compound has a strong chromophore in the UV range but is a white crystalline material, what can be said about the visual spectrum. In theory, what is required to change on the original chromophore to produce a visual spectrum?
37. Why is a diode-array UV detector commonly used in LC experiments?
38. What role does the choice of solvent play in a UV/Vis experiment (i.e., if toluene, hexane, acetone where possible choices)?
39. Is there high specificity in your UV/VIS experiment to differentiate two similar compounds?
40. Describe the use and limitations of a library of UV spectra from the diode-array experiment for drugs of abuse.
41. Define the following terms: single beam, double beam, diffraction grating, monochromator, photomultiplier, scan speed, slit width, resolution, frequency wavelength amplitude, intensity, absorbance, transmittance, electronic transitions, hyperchromic shift, bathochromic shift, hypochromic shift, auxochrome, chromophore, R-bands, K-bands, diode array, radiation source.
42. Draw a schematic of a diode array UV spectrophotometer. Label each part and explain what each does.
43. Explain ultraviolet spectroscopy to a jury. You may pick a particular drug to explain, if it helps.
44. Explain ultraviolet spectroscopy to a group of your peers. This should be a more technical explanation.