Organic solvents containing miscellaneous atoms, usually with strong end absorption. Therefore, when used as solvents, they can not be used less than the cutoff wavelength. For example, the cut-off wavelength of methanol and ethanol is 205nm. In addition, when the solvent is impure, it can also increase the interference absorption. Therefore, before testing for testing, should first check whether the solvent used in the vicinity of the wavelength used to meet the requirements, the solvent will be placed 1cm quartz absorption pool, the air is blank (that is, no matter in the blank light path) to determine its absorbance. The absorbance of the solvent and absorption tank shall not exceed 0.40 in the 220~240nm range, shall not exceed 0.20 in the 241~250nm range, shall not exceed 0.10 in the 251~300nm range, and shall not exceed 0.05 above 300nm.