4. When determining niobium, the fluorescence intensity of the Nb complex with lumogallion IREA was measured at liquid nitrogen temperature. To eliminate the influence of aluminum, ammonium oxalate was introduced. Standard solutions contained 0.025; 0.05; 0.10; 0.15 µg Nb in 1 ml. After adding the same reagents to 1 ml of the standard solution as in the case of the test, the fluorescence intensity of the frozen solutions (I) IS 4; 7; 13 and 21 rel.un. calculate the mass fraction (%) of niobium in the sample, if a weighed portion of the sample weighing m(g) was dissolved in a volumetric flask with a capacity of 100 ml, 1.0 ml of the resulting solution was taken for analysis and the fluorescence intensity Ix was measured.
Option 1.
m (g) 520
X8

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