Iridium (Ir)13 is the eighth element in Group VIII of the periodic table. It has an atomic number of 77, an atomic weight of 192.2, and valences of 1, 3, and 4. The average abundance of Ir in the earth’s crust is probably <0.001 ppm, and in groundwaters it is <0.1 mg/L. Iridium occurs uncombined with platinum and other metals. It is used in alloys with platinum in catalysts, thermocouples, electrodes, and wires.
The aqueous chemistry is controlled by complex compounds, although the solubility in natural waters is relatively unknown.
Perform analyses by the flame atomic absorption spectrometric method (Section 3111 B). The inductively coupled plasma/mass spectrometric method (Section 3125) also may be applied successfully in most cases (with lower detection levels), even though iridium is not specifically listed as an analyte in the method.