Source: modified from Xvlun ().Ītomic emission spectroscopy is ideally suited for multielemental analysis because all analytes in a sample are excited simultaneously. This is accomplished by the tangential flow of argon shown in the schematic diagram.įigure 10.58 Schematic diagram of an inductively coupled plasma torch. At these high temperatures the outer quartz tube must be thermally isolated from the plasma. The resulting collisions with the abundant unionized gas give rise to resistive heating, providing temperatures as high as 10 000 K at the base of the plasma, and between 60 K at a height of 15–20 mm above the coil, where emission is usually measured. An alternating radio-frequency current in the induction coils creates a fluctuating magnetic field that induces the argon ions and the electrons to move in a circular path. Plasma formation is initiated by a spark from a Tesla coil. The sample is mixed with a stream of Ar using a nebulizer, and is carried to the plasma through the torch’s central capillary tube. The ICP torch consists of three concentric quartz tubes, surrounded at the top by a radio-frequency induction coil. Because plasmas operate at much higher temperatures than flames, they provide better atomization and a higher population of excited states.Ī schematic diagram of the inductively coupled plasma source (ICP) is shown in Figure 10.58. A plasma’s high temperature results from resistive heating as the electrons and argon ions move through the gas. The plasmas used in atomic emission are formed by ionizing a flowing stream of argon gas, producing argon ions and electrons. We also expect emission intensity to increase with temperature.Ī plasma is a hot, partially ionized gas that contains an abundant concentration of cations and electrons. From equation 10.31 we expect that excited states with lower energies have larger populations and more intense emission lines. Where g i and g 0 are statistical factors that account for the number of equivalent energy levels for the excited state and the ground state, E i is the energy of the excited state relative to a ground state energy, E 0, of 0, k is Boltzmann’s constant (1.3807 × 10 –23 J/K), and T is the temperature in kelvin.
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