Indium (In) is the fourth element in Group IIIA in the periodic table. It has an atomic number of 49, an atomic weight of 114.82, and valences of 1, 2, and 3. The average abundance of indium in the earth’s crust is 0.19 ppm; in streams it is <0.01 μg/L; and in groundwaters it is <0.1 mg/L. Indium often occurs in combination with zinc ores, and sometimes with pyrites and siderite. Indium is used in alloys for bearings, brazing, solder, and in electrical devices.
Indium exists as In3+ and as a number of complex ions. Its solubility is controlled by the formation of the insoluble hydroxide. The metal and its compounds are toxic by inhalation.
Perform analyses by the electrothermal atomic absorption method (Section 3113 B). The inductively coupled plasma mass spectrometric method (Section 3125) also may be applied successfully in most cases (with lower detection levels), even though indium is not specifically listed as an analyte in the method.