32. Solving a chemistry problem

5. A meat sample weighing 0.15 g was burned in a muffle furnace, the residue was dissolved in hydrochloric acid and diluted with a solution of lanthanum salt to 5.00 ml to eliminate the interfering influence 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 Ca and the same amount of lanthanum salt as in the analyzed solution. The optical density of the analytical calcium line was measured at 422.67 nm using an atomic absorption spectrophotometer. Calculate the calcium concentration (mg/kg) using a calibration graph using the addition method if the following optical density values are obtained: Ax/2 = 0.050; A(x c1)/2 = 0.116; A(x c2)/2 = 0.185; A(x c3)/2 = 0.320.