11.3 Calcium Solution, Standard (1.00 mL = 0.400 mg calcium)— Suspend 1.000 g of calcium carbonate (CaCO3), dried at 180°C for 1.0 h before weighing, in approximately 600 mL of water and dissolve cautiously with a minimum of dilute HCl. Dilute to 1000 mL with water in a volumetric flask.
11.3.1 Alternatively, certified calcium stock solutions are commercially available through chemical supply vendors and may be used.