For preparation of tablet samples, three pieces of bismuth subcitrate tablet were powdered
in a mortar and homogenized. Each tablet contains bismuth subcitrate equivalent to 120 mg of bismuth oxide. Then,0.01 g of powdered sample was immersed in water and 1.0 mLconcentrated sulfuric acid. The mixture was dispersed under ultrasonication for 30 min then centrifuged and the supernatant solution was diluted with deionized water to the mark in a 100.0 mL volumetric flask