Atomic emission spectroscopy and the method of standard addition are used to determine the Na+ concentration and its uncertainty in an unknown sample. Increasing amounts of a 1.75 μg/mL standard Na+ solution are added to a series of volumetric flasks containing 15.00 mL of the unknown solution. The volumetric flasks are then diluted to a final volume of 200.0 mL. Atomic emission spectroscopy is then used to measure the emission intensity of each solution.