Assume your sample spots are 1 cm above the bottom of the TLC plate. What happens if you put the plate in a developing chamber that has 1.2 cm of developing solvent?
A. The solvent will move up the plate by capillary action faster.
B. The sample spots will become more concentrated.
C. The compounds to be analyzed will end up in the developing solvent.
D. The pencil marks will dissolve in the developing solvent.
Wouldn't you think C.
D is the answer. :)
It is C.
To answer this question, we need to understand the principles of thin-layer chromatography (TLC) and capillary action.
1. Thin-layer chromatography (TLC): TLC is a technique used to separate and analyze different compounds in a mixture based on their differential migration rates on a thin layer of adsorbent material (typically silica gel or alumina) coated onto a support (usually a glass plate or plastic sheet). During TLC, a sample is spotted onto the plate, and then it is placed in a developing chamber with a solvent.
2. Capillary action: Capillary action is the movement of a liquid within a narrow space or a porous material due to the forces of cohesion and adhesion. In TLC, capillary action is responsible for the solvent moving up the plate, carrying the compounds with it.
Now, let's analyze the given situation:
Assuming the sample spots are 1 cm above the bottom of the TLC plate and the developing chamber has 1.2 cm of developing solvent, we can infer the following:
A. The solvent will move up the plate by capillary action faster: This statement is incorrect. The height of the developing solvent in the chamber does not directly affect the speed of capillary action. Capillary action primarily depends on the properties of the stationary phase (adsorbent material) and the mobile phase (developing solvent), as well as the composition of the mixture being separated.
B. The sample spots will become more concentrated: This statement is also incorrect. The concentration of the sample spots is determined by the initial amount of material spotted onto the plate, not by the height of the developing solvent.
C. The compounds to be analyzed will end up in the developing solvent: This statement is incorrect. In TLC, the compounds being separated are retained on the stationary phase (adsorbent material) as the developing solvent moves up the plate. The compounds will typically form separate spots at different heights on the plate, allowing for analysis.
D. The pencil marks will dissolve in the developing solvent: This statement is uncertain. Whether the pencil marks dissolve in the developing solvent depends on the solvent used and the specific characteristics of the pencil marks. In general, pencil marks are relatively stable and not easily soluble in most common developing solvents used in TLC (such as hexane, ethyl acetate, methanol, etc.).
Based on the analysis, none of the options accurately describes what would happen if the plate were put in a developing chamber with 1.2 cm of developing solvent.