The GB/T 1 2690.16 - 2 010 standard specifies a method for the determination of fluorine content in rare earth metals and their oxides. This method is suitable for rare earth samples with fluorine content ranging from 0.010% to 0.50%. During the determination, the sample is dissolved with dilute nitric acid and then sodiumhydrate is added to separate fluorine from Miscellaneous elements. In a solution at pH 6.5~ 7.0, the potential difference of fluoride ions is measured by the fluoride ion selective electrode, and the fluorine content is calculated in combination with the Grignard mapping method. The standard details the required reagents, including the fluorine standard storage solution and the preparatory method of the standard solution, to ensure the accuracy and Reliability of the analysis.