Chromatography Practice Test

In TLC, the number of compounds in a mixture is determined by the number of distinct spots that appear on the plate after development. Each component interacts differently with the stationary phase and moves with the mobile phase to a unique extent, so it typically forms its own spot at a characteristic distance from the baseline. The solvent front distance is just used to calculate the Rf value for each spot; it does not count how many compounds are present. If all components happened to travel together with the same affinity, they would merge into a single spot, making it look like only one compound is present. When the separation works well, you’ll see multiple spots, each corresponding to a different compound; sometimes two or more compounds may co-elute and appear as one spot, in which case a different solvent system or visualization method can reveal additional spots.