Why is the wavelength of ultraviolet detector for the determination of acetylsalicylic acid 254nm?

the wavelength of the ultraviolet detector for measuring the content of acetylsalicylic acid is 254nm because

the drawing of the ultraviolet absorption spectrum: accurately weigh 5m g of acetylsalicylic acid, put it in a 1mL volumetric flask, add an appropriate amount of anhydrous ethanol, shake it to dissolve it, then dilute it to scale with anhydrous ethanol, shake it evenly, accurately measure 2mL, put it in a 5mL volumetric flask, add (. 1 m mol L L L sodium hydroxide solution 5mL, Shake well and scan at 19 ~ 358 nm by ultraviolet spectrophotometry to obtain the absorption spectrum of acetylsalicylic acid. From Figure 1, it can be seen that the appropriate wavelength is 296nm. Results and discussion 2. 1 Linear range determination.