A simple design for a multichannel spectrometer couples a monochromator with multiple detectors that can be positioned in a semicircular array around the monochromator at positions corresponding to the wavelengths for the analytes (Figure 10.59).įigure 10.59 Schematic diagram of a multichannel atomic emission spectrometer for the simultaneous analysis of several elements. This sequential analysis allows for a sampling rate of 3–4 analytes per minute.Īnother approach to a multielemental analysis is to use a multichannel instrument that allows us to simultaneously monitor many analytes. If the instrument includes a scanning monochromator, we can program it to move rapidly to an analyte’s desired wavelength, pause to record its emission intensity, and then move to the next analyte’s wavelength. 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. Sonntag, in Process Technologies for Water Treatment, Ed. The average total VUV-UV output radiation power reached 7 W. The optimum partial pressure of xenon is within 600–800 Pa, and that of bromine vapor, within 50–100 Pa. The operation regime was optimized with respect to the energy supplied to the glow discharge and the working gas mixture pressure and composition. An increase in the partial pressure of xenon in the working mixture from 130 to 800 Pa is accompanied by a decrease in the intensity of emission lines due to atomic bromine and an increase in the intensity of emission from xenon bromide molecules. The emission spectrum is formed by the molecular lines of xenon bromide at 282 nm and 220 nm and the atomic resonance lines of bromine at 163.3 and 157.6 nm. The working medium-a mixture of xenon and bromine vapor-was excited in a longitudinal glow discharge in a quartz tube with an interelectrode distance of 100 mm. The output characteristics of a small-size gas-discharge lamp emitting in the 160–300 nm wavelength range are reported.

Xenon atomic emission spectrum