The electronic energy level spacings for atoms are very specific for the element. As a result, the analysis of light emitted by atoms in an excited state can give information about the identity and amount of elements in a sample. In ICP, solutions containing metal ions are aspirated into an argon plasma in which they are converted to a free atom vapor. The high temperature of the plasma excites the atoms and they emit characteristic light upon relaxation to the ground state. The emitted light is analyzed and, in this way, the amount of metal present in the original sample can be determined. The ICP shown in the picture is a very sensitive technique for the determination of metals, and is used routinely in environmental work. For example, it can be used for the determination of lead in natural waters, soils or paints.