The solvent, show here in gray, rises up the TLC plate and carries with it samples A, B, and C, shown here in yellow, blue and green. Sample C is our analyte under examination, while samples A and B are two known compounds. Sample C separates into its component parts which are found to travel the same distance (approximately equal Rf's) as our two standards. Thus we are able to qualitatively determine what Sample C is composed of by running alongside it different trial compounds that we have reason to believe might be found in C. This is an excellent and necessary precursor to more conclusive analytical techniques.