Why can't you use an ink pen to mark a TLC plate?

Submitted by benny

Why is it that you are only supposed to use pencil to mark a TLC plate?
Why can't I use a pen?

Replies

Submitted by Matt

You can't use a pen because the ink will travel up the TLC plate with the TLC solvent, just like your chemical samples do.
You can only spot/label/mark TLC plates using a pencil. The graphite in a pencil will not run up the plate!
For an overview of TLC, see:
www.mendelset.com/articles/683/thin-layer-chromatography-tlc