Question

While Prepping Eluent Chambers and TLC Plates, why does the chemist carefully trace a baseline with a pencil straight across the plate at least 1-2 cm from the bottom of the plate? Check all that are true.

a. The baseline must be above the solvent level in the TLC chamber so that the baseline spots do not dissolve into the mobile phase at the bottom of the chamber.
b. The baseline needs to be the same distance from the bottom of the plate for all of the spots in order to calculate accurate Rf.
c. The baseline does not need to be straight; the mobile phase will move the spots along the stationary phase regardless of where the baseline starts. You can spot wherever you want.
d. A pencil is used instead of a pen because a pen will result in ink streaking across the plate, making analysis of the plate difficult or impossible.

Answer 1

The chemist traces a baseline with a pencil straight across the TLC plate at least 1-2 cm from the bottom of the plate for several reasons: to prevent dissolving of the baseline spots into the mobile phase, to calculate accurate Rf values, and to avoid ink streaking.

Step-by-step explanation:

The chemist carefully traces a baseline with a pencil straight across the TLC plate at least 1-2 cm from the bottom of the plate for several reasons:

1. The baseline must be above the solvent level in the TLC chamber so that the baseline spots do not dissolve into the mobile phase at the bottom of the chamber.
2. The baseline needs to be the same distance from the bottom of the plate for all of the spots in order to calculate accurate Rf (retention factor) values.
3. A pencil is used instead of a pen because a pen will result in ink streaking across the plate, making analysis of the plate difficult or impossible.