Hg discharge lamp

The common source for a uv detector is a Hg discharge lamp or a xenon discharge lamp with suitable filters to isolate the desired wavelengths. Compounds with benzene rings are detected readily using the Hg source, but other compounds are not. A way to improve this is by vacancy enhancement. What is done is to place a compound in the buffer that is readily detectable. When the sample passes the detector, the sample has created a "vacancy" in the liquid, and the detector response diminishes, indicating the presence of a compound. Chromate is a favorite at the moment as a high mobility ion. Phthalate and p-hydroxybenzoate are lower mobility ions. 

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. 

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. 

Source of Radiation The radiation source for FAAS instrumentation is quite similar to that of other AAS techniques, such as ETAAS or CVG-AAS (CV-AAS and HG-AAS). The one most commonly applied is the line source (LS), which generates a characteristic narrowline emission of a selected element. There are two principal LSs for AAS the hollow cathode lamp (HCL) and the electrodeless discharge lamp (EDL).8... 

The spectral characteristic of this light depends on the kind of the source the incandescent lamps are used primarily as sources of polychromatic visible light characterized by a continuous spectrum electrical discharge lamps produce band or line spectra in UV, visible and near-IR regions, whereas resonance lamps emit resonance radiation of atoms and their ions in the form of line spectra and can be used as sources of monochromatic light, eg Hg (184.9 and 253.7nm), Cd (228.8 and 643.8nm), Na (589.0nm), Zn (213.8, 330.0, 334.5, and 636.2nm), Kr (116.5 and 123.6nm), Xe (129.6 and 147.0nm) [1]. 

Emission Spectrum. Several sources are suitable for exciting the emission spectrum of I2. In previous editions of this text, the use of a low-pressure mercury discharge lamp was described, in which the green Hg line at 546.074 nm causes a transition from... 

Such down-conversion phosphors are needed for energy efficient Hg-free lamps, which are driven by a Xe/Ne discharge. In order to establish f-f transitions with VUV-excitation and to avoid band-to-band absorption by the host lattice, large band-... 

An alternative to HCL are electrodeless discharge lamps (EDI) whose light intensity is about 10-100 times greater but are not as stable as HCL. They are made of a sealed quartz tube that contains a salt of the element of interest along with an inert gas. An RF fields is used to excite the gas which in turn causes the metal to be ionized. These lamps are in general reserved for elements such as As, Hg, Sb, Bi and P. 

While some of the mid-IR sources emit light below 400 cm the intensity drops off. A more useful source for the far-IR region is the high pressure mercury discharge lamp. This lamp is constructed of a quartz bulb containing elemental Hg, a small amount of inert gas, and two electrodes. When current passes through the lamp, mercury is vaporized, excited. 

In the analysis of inorganic anions using acetonitrile-water (3-1-7) containing citric acid and hexadecyltrimethylammonium hydroxide as eluent. Wheals reported that bromide, cyanide, dithionite, ferrocyanide, iodide, metabisulfite, nitrite, perborate, peroxide, sulfide, thiocyanate and thiosulfate respond at a GCE (-1-0.75 V vs Ag/AgCl). Dou and Krull have further shown that post-column irradiation (low pressure Hg arc discharge lamp) can facilitate the EC detection of chromate, dichromate and perchlorate and give improved sensitivity for thiocyanate. Despite this work, however, the application of EC detection to the analysis of these ions in biological systems has not been reported as yet. 

Vapour discharge lamps have been available for some elements (e.g. Cd, Ga, Hg, In, K, Na and Tl) since the inception of commercial instrumentation, although such devices are limited to the volatile elements and are therefore not universal. 

Cathode ray tubes Equipment containing CFCs, HCFCs, or MFCs present in foam Gas discharge lamps Fluorescent coating must be removed Must be properly extracted and destroyed Mercury (Hg) must be removed... 

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