Abstract: A test strip for determining the concentration of a component in a liquid composition is disclosed. The test strip comprises a carrier sheet coated with a layer of an adsorbent, and a chemical dye deposited on the test strip near but spaced apart from a bottom edge of the test strip. In some embodiments, the test strip is a thin-layer chromatography (TLC) plate, and the retention factor of the chemical dye varies according to the concentration of the component in the liquid composition. A user can determine the concentration of the component based on the migration distance of the chemical dye on the test strip in a chromatography process. The test strip can be used to perform a fast and visual test to determine the ethanol content in a fuel sample.