Inductively coupled plasma (ICP) torches are used in atomic emission spectroscopy, atomic absorption spectrometry, and Mass spectrometry. Plasma is considered the 4th state of matter. A Plasma is charged particles of gas and can reach extremely high temperatures; a star is an example of a plasma. In ICPs the energy to ionize the gas is supplied by electric currents produced by an induction field (a magnetic field varied over time). When samples are introduced into the plasma the elements in the sample are ionized and emit and absorb at specific wavelengths of light. A photo detector is used to detect the absorption or emission. The specific wavelength will identify the element and the amount of absorption or emission is directly proportional to concentration. ICP is preferred over flame emission or flame absorption due to the lower background of the ICP. In ICP MS the ICP is used to ionize the sample before it enters the magnetic field of the Mass spectrometer.