62. Solving a chemistry problem

5. For standard solutions of caffeine, theobromine and theophylline during thin layer chromatography, the values of retention factors - Rf were determined, which turned out to be 0.87, 0.65 and 0.46, respectively. Determine the qualitative composition of the analyzed mixture if its chromatogram under the same conditions has two spots at a distance of 3.9 cm and 2.1 cm from the start line, and the solvent has traveled a distance of 4.5 cm. Draw a view of the chromatogram of the test solution. How can spots of analytes be detected on a chromatogram?