In paper chromatography, why must the starting line be drawn with pencil?

Thanks!

If you drew it in ink the solvent would move the components of the ink (at different rates of course) up the paper to various levels and your "starting line" wouldn't be there anymore.

In paper chromatography, the starting line is typically drawn with a pencil because pencil marks are insoluble in water and most organic solvents. This means that when the solvent (mobile phase) moves up the paper, it won't dissolve the pencil line and cause it to spread or blur.

To draw the starting line using a pencil, follow these steps:

1. Place the paper chromatography paper on a flat surface.
2. Use a ruler to mark a line near the bottom of the paper where you want the solvent to start.
3. Take a pencil and lightly draw the line on the marked spot.
4. Make sure the line is thin and straight.
5. Allow the pencil line to fully dry before proceeding to the next steps.

By drawing the starting line with a pencil, you ensure that it remains intact and visible throughout the chromatography process. This allows for accurate measurement and analysis of the results. If pen or marker is used instead, it may dissolve or spread during the chromatography process, making it difficult to interpret the separation of components.