137. Solving a chemistry problem

137. Solving a chemistry problem

A sample of animal tissue weighing 0.25 g was burned in a muffle furnace, the residue was dissolved in hydrochloric acid and diluted with a lanthanum salt solution to 5.00 ml to eliminate the interfering effect of phosphate ions. To four equal portions of the analyzed solution were added equal volumes of standard calcium solutions containing C0 = 0, C1 = 2.0 C2 = 4.0 C3 = 8.0 μg / ml calcium and the same amount of lanthanum salt as in the analyzed solution. The optical density of the analytical calcium line (422.67 nm) was measured on an atomic absorption spectrophotometer. Calculate the calcium concentration (μg / ml) in the following samples, using the construction of a calibration graph by the addition method, if the measured absorbance values ​​are Ax2 = 0.100, A (x C1) / 2 = 0.185, A (x C2) / 2 = 0.260 A (x C3) / 2 = 0.410, respectively.