P and F contained in organic compounds were determine by using lanthanides after decomposition in an O flask. All lanthanides(III) could be used for determing P by direct titration, of which Dy-Lu lanthanides could prevent the interference of S. P in F-contg. sample could be determine by adding concentrated H2SO4 into the absorption medium and concentrating to remove F-. La-Dy lanthanides were used for determing F. The excess lanthanides were determine by EDTA back-titrn. The percentage of F can be obtained after the amount of P and the total content of P and F were determine The max. error of determing P was ?.20%, and F ?.30%.

Key words: COMPLEXOMETRY, FLUORINE, THULIUM, ORGANO PHOSPHORUS COMPOUNDS, LANTHANON, PHOSPHORUS, CERIUM, ORGANO FLUORINE COMPOUNDS, LANTHANUM, SIMULTANEOUS DETERMINATIONS, GADOLINIUM, DYSPROSIUM, SAMARIUM, EUROPIUM, LUTETIUM, EDTA TITRATION, TERBIUM, PRASEODYMIUM, ERBIUM, NEODYMIUM, HOLMIUM, YTTERBIUM