The SN/T 5051-2018 standard specifies a method for the determination of fluorine, chloride, sulfate and nitrate ions in water-soluble phosphoric acid salts using Ion chromatography. It is suitable for the determination of fluorine (F), chloride (Cl), sulfate (SO4 ^ 2-) and nitrate (NO3 ^ -) in sodium dihydrogen phosphoric acid and potassium hydrogen phosphoric acid, with lower limits of 2.0 mg/kg, 4.0 mg/kg, 5.0 mg/kg and 5.0 mg/kg, respectively. Measurement ranges are 2.0 mg/kg to 1000 mg/kg, 4.0 mg/kg to 1000 mg/kg, 5.0 mg/kg to 2000 mg/kg and 5.0 mg/kg to 2000 mg/kg respectively. The standard describes in detail the sample pretreatment, including sodiumhydrate dissolve and Ion Chromatography operation steps. All reagents used must meet the analytical purity requirements, and the water is first-class water in accordance with GB/T 6682.