Dry Lab interpretation - Apply Your Knowledge **Reinterpretation of plate design

Question

Dry Lab interpretation - Apply Your Knowledge **Reinterpretation of plate designation may be necessary** Each stain and the functional groups it reveals:

1. Why do some spots react with the molybdenum stain and not ninhydrin? Why do some spots react with ninhydrin and not molybdenum?

2. Why are not all the positive iodine spots also positive with the molybdenum spray?

3. What can you say about the number of compounds in each pill/egg?

4. Why would we include gelatin and fruit pectin in the analysis?

5. In general terms, what can you say about the polarity of each of these spots?

6. Why do you think that these tests are all performed instead of just one?

7. In general terms, what does each spot mean on the TLC plate?

8. Using the data above , what functional groups can you definitively say are present in each spot for each pill/egg? Redraw the TLC’s below and write the functional groups that you think correspond to each spot.

Each stain and the functional groups it reveals: TLC Double Plate Molybdenum Phosphate #1 lodune Double Bonds 254 U TLC Plate DagendorffCholine #2 TLC Plate Ninhydrin #3 Free Amines (R-NH2 Ri C2 R2 Structure of Choline: R3 R4

Explanation / Answer

For colorless compounds, a visualizing technique is needed to observe TLC results. Stains can be applied by spraying or by dipping of a plate into solution. The latter is by far more convenient. However, in order to work, the right the stain solution SHOULD NOT dissolve analyte spots. For example, permangantate stain is perfect for most not-too-polar organic compounds while acetone-based nynhydrin stain is excellent for amino acids. If analyte solubility in stain solution is inevitable, try to dip the plate as quickly as possible, and then immediately wipe off an excess of stain. Still, there will be some artificial tails added to spots. Also, do not forget, if a compound that must be analyzed is volatile, it may evaporate before the stain visualizes it, especially if heating is required for visualization.

Related Questions

Navigate

• Browse (All)
• Browse D
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.