Cesium (Cs) is the sixth element in Group IA of the periodic table. It has an atomic number of 55, an atomic weight of 132.90, and a valence of 1. The average abundance of Cs in the earth’s crust is 2.6 ppm; in soils it is 1 to 5 ppm; in streams it is 0.02 mg/L; and in groundwaters it is generally <0.1 mg/L. Cesium is found in lepidolite and in the water of certain mineral springs. 137Cs, with a 33-year half-life, is widely dispersed on the earth’s surface as a result of the radioactive fallout from the atmospheric testing of nuclear weapons. Cesium compounds are used in photoelectric cells, as a catalyst, and in brewing. Some cesium compounds are fire hazards.
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 cesium is not specifically listed as an analyte in the method.