When preparing a TLC slide of a reference standard material (RSM), a solvent or mixture of solvents is used to dissolve the RSM and transfer it into the TLC plate. How does its polarity affects the Rf of the RSM?

The better the RSM dissolves in the solvent, the higher the Rf (retention factor) will be, and the further the RSM will move. If the RSM is a polar compound, increasing the polarity of the solvent will increase the Rf of the RSM. If the RSM isn't a polar compound, an increasingly polar solvent will decrease the Rf.