Radio-frequency EDLs

Electrodeless discharge lamps (EDLs) emit radiation as a result of radio frequencies providing the exciting energy. 

A typical EDL consists of a hermetically sealed quartz envelope containing an inert gas (Ar) at very low pressure and the element or salt of the target element. In order to ionize the inert gas, micro-wave radiation (approximately 100 MHz) or, as is usually the case, radio frequency (RF) radiation (from 100 kHz to 100 MHz) is applied. Commercially available RF EDLs have a built-in starter, run at 27 MHz, which provides a high voltage spark to ionize the filler gas to initiate the discharge. 

Electrodeless discharge lamp (EDL). This is a tube which contains the element to be measured in a readily vaporized form (often as iodides). A discharge is produced in the vapour by microwave or radio frequency induction. The lamp emits very intensive characteristic radiation of the analyte. 

Radiofrequency EDLs. The intensity of these lamps may be lower than that of microwave lamps, but they give better short and long term stability without the need for a thermostat. The radio frequency commonly employed is 27.12 MHz. Radiofrequency EDLs are available for about 15 elements, and they are particularly suitable for routine applications of the volatile elements arsenic, selenium, antimony, tellurium, and phosphorus. 

Electrodeless discharge lamps (EDL), powered with energy in the radio-frequency range, were used as early as 1928 by Jackson, and in 1948 Meggers used them to determine hyperfine structure of atomic spectra. These lamps produce narrow-line, high-intensity spectra with little self-absorption. They would appear, therefore, to be promising sources for atomic absorption. 

EDLs are available commercially for fifteen or more elements. Their performance is not as reliable as that of the hollow-cathode lamp, but for elements such as Se, As, Cd. and Sb, EDLs exhibit better detection limits than do hollow-cathode lamps. This occurs because EDLs for these elements are more intense than the corresponding hollow-cathode lamps, and thus, EDLs are quite useful in determining these elements. Figure 9-12 is a schematic of a commercial EDL, which is powered by a 27-MHz radio-frequency source. 

Gunning, Pertel, and their coworkers reported the photochemical separation of mercury isotopes [92-95] in a flow reactor which consisted of a microwave-operated discharge lamp [52, 96] cooled by a flowing film of water. A filter cell and a circulation system, to prevent heating of the filter solution and the cell, were placed concentrically and coaxially with the lamp. A similar reactor, for small-scale laboratory photolysis of organic compounds in the solution or gas phase, has been proposed by Den Besten and Tracy [91]. In this arrangement the EDL was placed in a reaction solution and was operated by means of an external microwave field from a radio or microwave-frequency transmitter (Fig. 19.11). The quantum output of the lamp was controlled by changing the output of the trans-... 

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