Electrodeless discharge lamps microwave-excited

A microwave-assisted, high-temperature, and high-pressure UV digestion reactor has been developed by Florian and Knapp [44] for analytical purposes. The apparatus consists of the immersed electrodeless discharge lamp operating as a result of the MW field in the oven cavity (Fig. 14.8). An antenna fixed to the top of EDL enhanced the EDL excitation efficiency. Another interesting MW-UV reactor has... 

Where vapour discharge lamp sources exist (for volatile elements such as Hg, Na, Cd, Ga, In, T1 and Zn) they can be used. Hollow-cathode lamps are insufficiently intense, unless operated in a pulsed mode. Microwave-excited electrodeless discharge lamps are very intense (typically 200-2000 times more intense than hollow-cathode lamps) and have been widely used. They are inexpensive and simple to make and operate. Stability has always been a problem with this type of source, although improvements can be made by operating the lamps in microwave cavities thermostated by warm air currents. A typical electrodeless discharge lamp is shown in Fig. 6.3. 

In the hollow cathode lamps of these relatively volatile elements self-absorption at low discharge currents may also be considerable and even self-reversal may take place. This is not the case with electrodeless discharge lamps. They consist of a quartz balloon in which the halogenide of the element is present. The analyte spectra are excited with the aid of a high-frequency (MHz range) or a microwave field (GHz range), supplied e.g. through an external antenna. 

High-intensity sources other than hollow cathode tubes also have been investigated. Most promising are the microwave-excited electrodeless discharge lamps. These lamps produce very high-intensity, sharp line spectra but suffer stability problems and generally have short lifetimes compared to hollow cathode tubes. 

Electrodeless discharge lamps EDLs employ either microwave energy (microwave-excited EDLs) or radiofrequency energy (radiofrequency-excited EDLs)... 

Electrodeless discharge lamps are used less frequently than the hollow-cathode lamps except for analytes such as arsenic and selenium. These lamps may be excited using either microwave energy (although these tend to be less stable) or radiofrequency energy. The radiofrequency-excited lamps are less... 

Ideally, the emission line used should have a half-width less than that of the corresponding absorption line otherwise equation (8.4) will be invalidated. The most suitable and widely used source which fulfils this requirement is the hollow-cathode lamp, although interest has also been shown in microwave-excited electrodeless discharge tubes. Both sources produce emission lines whose halfwidths are considerably less than absorption lines observed in flames because Doppler broadening in the former is less and there is negligible collisional broadening. 

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