by accurately weighing 20 mg of calcium thioglycolate trihydrate
into a 1.5 mL of sample vial. 1 mL of water was added and then vortex-mixed. A series of standard solutions at the final concentra- tions of 0.006, 0.025, 0.125, 0.250, 0.500 and 1.000 mg mL−1 were
made and kept in dark to avoid possible photodissociations [16].