Electrodeless discharge lamps

EDLs are very intense, stable emission sources. They provide better detection limits (DLs) than HCLs for those elements that are intensity limited either because they are volatile or because their primary resonance lines are in the low-UV region. Some elements like As, Se, and Cd suffer from both problems. For these types of elements, the use of an EDL can result in a LOD that is two to three times lower than that obtained with an HCL. EDLs are available for many elements, including antimony, arsenic, bismuth, cadmium, germanium, lead, mercury, phosphorus, selenium, thallium, tin, and zinc. Older EDLs required a separate power supply to operate the lamp. Modem systems are self-contained. EDLs cost more than the comparable HCLs. 

Most modern AAS systems have coded lamps that are recognized by the spectrometer software, which can then set up the analysis parameters automatically. The instrument knows that a copper lamp or a calcium lamp has been inserted and can apply the default analytical conditions without analyst intervention. 

Having explained why narrow line sources are needed for AAS, in Section 6.2.6, a new high-resolution AAS using a continuum source will be introduced. 

The atomizer is the sample cell of the AAS system. The atomizer must produce the ground-state free gas-phase atoms necessary for the AAS process to occur. The analyte atoms are generally 

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Electrical units 503, 519 Electrification due to wiping 77 Electro-analysis see Electrolysis and Electrogravimetry Electrochemical series 63 Electro-deposition completeness of, 507 Electrode potentials 60 change of during titration, 360 Nernst equation of, 60 reversible, 63 standard 60, (T) 62 Electrode reactions 505 Electrodeless discharge lamps 790 Electrodes antimony, 555 auxiliary, 538, 545 bimetallic, 575... 

EDL Electrodeless discharge lamp ETA AES Electrothermal atomisation atomic... 

Additionally, advanced tools for special applications are offered, including provisions for parallel reflux, solvent extraction, and hydrolysis, as well as electrodeless discharge lamps for photochemistry (Fig. 3.10). A detailed description of these accessories can be found on the Milestone website [11],... 

UV radiation, certainly not sufficient to disrupt the bonds of common organic molecules. We therefore assume that, essentially, photoinitiation is responsible for a chemical change and MW radiation subsequently affects the course of the reaction. The objective of microwave photochemistry is frequently, but not necessarily, connected to the electrodeless discharge lamp (EDL) which generates UV radiation when placed in the MW field. 

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... 

EDL stands for electrodeless discharge lamp. It is an alternative to the hollow cathode lamp as a light source in atomic absorption spectroscopy. 

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

Figure S.4 shows a calibration graph of arsenic concentrations obtained by using a Perkin Elmer 2100 atomic-absorption system bnked to a P.S. Analytical hydride/vapour generator (PSA 10.003). An electrically heated tube has been used in this work and the spectral source was an electrodeless discharge lamp. Alternatively, a flame-heated tube can be used.

As we have seen, a narrow line source is required for AAS. Although in the early days vapour discharge lamps were used for some elements, these are rarely used now because they exhibit self-absorption. The most popular source is the hollow-cathode lamp, although electrodeless discharge lamps are popular for some elements. 

A diagram of such a lamp is shown in Fig. 2.3 [taken from Barnett ai, At. Absorpt. Newsl. 15, 33 (1976). This paper gives a good account of the analytical performance of electrodeless discharge lamps]. 

High intensity is not a source requirement in AAS and therefore electrodeless discharge lamps will not replace hollow-cathode lamps. However, for those elements that produce poor hollow-cathode lamps (notably arsenic... 

Cutaway diagram of an RF-excited electrodeless discharge lamp. 

Q. What are the advantages of radiofrequency-excited electrodeless discharge lamps ... 

It has been shown that a high frequency of modulation of the electrodeless discharge lamp (e g. 10 kHz) is advantageous. This frequency is well away from the low frequency of flame noise. If the amplifier is locked-in to this high frequency via a reference signal, an optimum signal-to-noise ratio is achieved. 

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. 

Q. What advantages are offered to AFS by (i) electrodeless discharge lamps and (ii) lasers ... 

Vapour discharge lamp. See Electrodeless discharge lamp Vapour generation. 

By far the most common lamps used in AAS emit narrow-line spectra of the element of interest. They are the hollow-cathode lamp (HCL) and the electrodeless discharge lamp (EDL). The HCL is a bright and stable line emission source commercially available for most elements. However, for some volatile elements such as As, Hg and Se, where low emission intensity and short lamp lifetimes are commonplace, EDLs are used. Boosted HCLs aimed at increasing the output from the HCL are also commercially available. Emerging alternative sources, such as diode lasers [1] or the combination of a high-intensity source emitting a continuum (a xenon short-arc lamp) and a high-resolution spectrometer with a multichannel detector [2], are also of interest. 

Kl4n, P., Literdk, J. and H4jek, M., The electrodeless discharge lamp a prospective tool for photochemistry,... 

An atomic fluorescence spectrometric determination of selenium was first reported by Dagnall et al. [185] using a dispersive spectrometer equipped with an air-propane flame, giving a detection limit of 0.25 xg/ml of selenium on aspiration of aqueous solutions using a pneumatic nebuliser. Fluorescence from the 204 nm selenium resonance line was observed when the flame was irradiated by radiation from a selenium electrodeless discharge lamp, the optical axis of which was aligned at 90 °C to the optical axis of the monochromator. 

In AAS the hollow cathode lamp (HCL) is the most important excitation source for most of the elements determined. However, sufficient light must reach the detector for the measurement to be made with good precision and detection limits. For elements in this table with intensities of less than 100, HCLs are probably inadequate, and other sources such as electrodeless discharge lamps should be investigated. 

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