GB/T 7485-1987 is a water quality testing standard. Spectrophotometric method, specs-trophotometry is used to determine the total arsenic content in water. Arsenic is a toxic element that may exist in both natural water bodies and industrial wastewater, and is extremely harmful. The standard specifies the whole process from the digestion of water samples, the reaction with reagents to generate red colloidal silver, to the determination of Absorbance by spectrophotometer and the calculation of total arsenic content. The operation specification and reliable results are suitable for all kinds of water sample testing, providing key technical support for water quality monitoring, drinking water safety and pollution prevention.