Which statement about the baseline in TLC is true?

Which statement about the baseline in TLC is true?

• A. It is the top of the plate.
• B. It is the line where samples are spotted.
• C. It marks the solvent front.
• D. It is the edge of the plate.

Answer: (D)

In TLC the baseline is the origin line from which all sample migrations are measured. It’s the line where the spots are applied, so it defines where the journey of each component begins as the solvent moves up the plate. The solvent front is a separate marker—the furthest point reached by the mobile phase during development, used to calculate Rf values. The top edge or outer boundary of the plate isn’t what defines the baseline.

In TLC the baseline is the origin line from which all sample migrations are measured. It’s the line where the spots are applied, so it defines where the journey of each component begins as the solvent moves up the plate. The solvent front is a separate marker—the furthest point reached by the mobile phase during development, used to calculate Rf values. The top edge or outer boundary of the plate isn’t what defines the baseline.