Question

In TLC, what will happen if the initial spot is very large when preparing a plate?

Answer 1

The biggest problem you will encounter, poor resolution. If the spot is too big because the sample is too highly concentrated, then the resolution will be poor because too much compound has been loaded onto the the TLC plate. The tell-tale sign that this has occurred is if the spot streaks all the way up the plate. However, if the sample is too dilute and the spot is too big because multiple superimposed applications of the sample had to be made in order for it to be seen, then the resolution of the plate will decrease because the baseline is too wide and, therefore, not level.