As mentioned before, this project required dyes that could be excited by UV light in the solid state, so 7-(Diethylamino)-coumarin-3-carboxylic acid and 6,7-Dihydroxycoumarin-3-carboxylic acid were selected. The two dyes are both soluble in organic solvents, so Dimethylformamide (DMF) which is common in the laboratory was selected as the solvent in this project. After testing, the suitable solution formula is as follows: The sample preparation method was similar to before, the sampling devices and sampling height were the same, but the difference was the sampling time, which was due to the different properties (viscosity and surface tension) of the organic solvent DMF and water.