Polychromator system

The nebulized sample is exitated in an argon-plasma at approximately 10000 Kelvin. A spectrometer with a polychromator system can determine several elements by measuring their specific emission wavelength with photomultipliers as sensitive detectors. The system requires one photomultiplier for each detectable element. The detection limits of this modem technique are usually between those of the Graphite-Furnace- and the Flame-AAS. The advantages of this system are the very high... 

Botto, R.l. (1981). A proposed dual polychromator system for reducing interferences in multielement ICPES. ICP Inf. Newslett., 6, 527-543. 

Commercial DC arc emission spectrometers and commercial spark spectrometers are available as stand-alone laboratory instruments. This list is not comprehensive, but examples include a DC arc ClD-based EcheUe system from Thermo Elemental (www.thermoelemen-tal.com), a multiple polychromator spark system with PMT detectors from Spectro Analytical Instruments (www.spectro-ai.com), and a spark spectrometer polychromator system with PMT detectors from Jobin Yvon, Inc. (www.jyhoriba.com). Many instrument companies make portable spark instruments, some small enough to be handheld, for use in sorting metal alloys at scrap yards, confirming the identity of alloys received at loading docks. 

The selection of non-interfered lines is more critical for polychromator systems due to the limited number of channels. The major requirement is that the line is not spectrally interfered and provides sufBcient sensitivity. However, for the determination of minor and major components less sensitive lines must also be included to allow for a better dynamic range. 

The second main type of system is the polychromator system for simultaneous scanning. The polychromator systems scan many wavelengths simultaneously, i.e., several elements are determined simultaneously at higher speeds than are possible with monochromator systems. It then moves on to the next sample. A typical system is shown in Figure 11.5. 

Figure 11.5 Polychromator system for inductively coupled plasma atomic emission...

Direct-reading polychromators (Figure 3b) have a number of exit slits and photomultiplier tube detectors, which allows one to view emission from many lines simultaneously. More than 40 elements can be determined in less than one minute. The choice of emission lines in the polychromator must be made before the instrument is purchased. The polychromator can be used to monitor transient signals (if the appropriate electronics and software are available) because unlike slew-scan systems it can be set stably to the peak emission wavelength. Background emission cannot be measured simultaneously at a wavelength close to the line for each element of interest. For maximum speed and flexibility both a direct-reading polychromator and a slew-scan monochromator can be used to view emission from the plasma simultaneously. 

Figure 25-20 Photodiode array ultraviolet detector for HPLC. (a) Dual-beam optical system uses grating polychromator, one diode array for the sample spectrum, and another diode array for the reference spectrum. Photodiode arrays are described in Section 20-3. (fc>) Reversed-phase chromatography (using C18-silica) of sample containing 0.2 ng of anthracene, with detection at 250 nm. Full-scale absorbance is 0.001. (c) Spectrum of anthracene recorded as it emerged from the column. [Courtesy Perkln-Elmer Corp.. Norwalk. Cl]...

Schramel [103] discusses the conditions for multi-element analysis of over 50 trace elements, giving detection limits. Wolnik [104] described a sample introduction system that extends the analytical capability of the inductively coupled argon plasma/polychromator to include the simultaneous determination of six elemental hydrides along with a variety of other elements in plant materials. Detection limits for arsenic, bismuth, selenium and tellurium range from 0.5 to 3 ng/ml and are better by at least an order of magnitude than those obtained with conventional pneumatic nebulisers, whereas detection limits for the other elements investigated remain the same. Results from the analysis of freeze-dried crop samples and NBS standard reference materials demonstrated the applicability of the technique. Results obtained by the analysis of a variety of plant materials are presented in Table 7.10. 

Hahn et al. [105] used a hydride generation/condensation system with an ICP polychromator for the determination of arsenic, bismuth, germanium, antimony, selenium and tin in plant materials. 

Figure 7.6. Hydride generation/condensation systems interfaced to an ICAP polychromator. D1 and D2 desiccant tubes I, II and III three-way valves. From [115]...

The detection system can be either single channel, detecting one element at a time, or multi-element, with a polychromator detecting many elements simultaneously. Initially the GC-MIP systems were not popular. This was due to the lack... 

Comparison of Fig. 1, which depicts a conventional CD system, and Fig. 4 shows the primary difference in the two approaches to be in the type and location of the wavelength dispersion device. For multichannel detection, the monochromator has been replaced by a polychromator which does not possess an exit slit to define a wavelength interval. For multichannel detection, the location (pixel) on the multichannel device defines the wavelength of interest. In conventional approaches, the monochromator is placed after the source in order to limit the UV exposure of the sample. However, in the multichannel arrangement, the polychromator is located after the sample to allow the sample to be... 

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