This standard specifies the method for the determination of fluorine in light burning mg by Ion selective electrode method. It is suitable for the determination of fluoride content in light burning mg, and the measurement range is 0.010% to 0.15% mass fraction. The sample is first analyzed by muriatic acid under microwave action, sodium citrate is added as a masking agent, and the measurement potential is carried out by fluorine Ion selective electrode and Calomel electrode at pH 6 to pH 6.5. The fluorine content in the sample is calculated by the measurement potential of the standard solution. The reagents used include muriatic acid solution (1 + 1), sodiumhydrate solution (200 g/L), and sodium citrate solution (1 mol/L).