28. Solving a chemistry problem

69th century A neutral aqueous solution of riboflavin (vitamin B2) is characterized by an absorption spectrum with a maximum at a wavelength of 450 nm and a fluorescence spectrum with a maximum at 535 nm.
For the fluorimetric determination of vitamin B2 in a crystalline preparation using the single standard method, a sample of the preparation weighing m was dissolved in water in a volumetric flask with a capacity of Vk(A), the volume of the solution was adjusted to the mark with water, and the analyzed solution was obtained (solution A). An aliquot of solution A with a volume of Va(A) was taken into a volumetric flask with a capacity of Vk(B), diluted with water to the mark, and the test solution (solution B) was obtained. 8-10 ml of the test solution was transferred to the fluorimeter cuvette and its fluorescence intensity Ix was measured (in arbitrary units - according to the instrument readings) with pre-selected primary and secondary light filters.
Under the same conditions, the fluorescence intensity Ist of a standard solution with a precisely known concentration of vitamin B2 Cst was measured.
Using the data below, calculate the mass fraction (%) of vitamin B2 in the crystalline preparation. What condition is mandatory for the fluorimetric determination of a substance in the studied concentration range using the single standard method?
What is the principle of choosing primary and secondary filters for fluorimetric measurements?
variant c) m, d Vk(A), ml Va(A), ml Vk(B), ml Ix Cst, μg/ml Ist
0.0150 500 1.00 100 72 0.30 74