Instrumentation echelle spectrometer

It should also be noted at this point that a multichannel detector can have multiple detector elements along two axes, one parallel to the direction of wavelength dispersion, and one perpendicular. The latter is parallel to the entrance slit in most dispersive instruments. For example, a CCD may have 1024 pixels along the wavelength axis and 256 along the vertical axis, for a total of 262,144 independent elements. This second dimension of the detector may be used in a variety of applications involving Raman imaging, multiple detection tracks, or echelle spectrometers. 

In addition, Echelle spectrometers are often used [50], By combination of an order-sorter and an Echelle grating either in parallel or in crossed-dispersion mode, high practical resolution (up to 300 000) can be realized with an instrument of fairly low focal length (down to 0.5 m) (Fig. 94). Therefore, the stability as well as the luminosity are high. By using an exit slit mask with a high number of preadjusted slits, highly flexible and rapid multielement determinations are possible. 

Most commercial AAS systems have the monochromator, optics, and detector designed for the measurement of one wavelength at a time they are single-element instruments. There are a few systems available that do perform multielement determinations simultaneously, using an Echelle spectrometer (discussed in Chapter 2) and a bank of HCLs all focused on the atomizer. The limitation to this approach is not the sources or the spectrometer or the detector, but the atomizer. The atomizer can only be at one set of conditions, and those conditions will not necessarily be optimum for all of the elements being measured. There will be a tradeoff in detection limits for some of the elements. 

Sequential and simultaneous ICP systems of many types are available from numerous instrument manufacturers. Most are available in radial or axial view, or both. Most spectrometers can be purged to reach 160 nm. Examples of some of the companies who make ICPs and DCPs are given. Jobin Yvon, Inc. makes a line of PMT-based high-resolution sequential systems, simultaneous systems, and combination sequential-simultaneous systems. PerkinElmer Inc. makes a scanning ICP with CCD detection, and a line of simultaneous CCD-based Echelle systems. Leeman Laboratories, Inc. makes an Echelle ICP spectrometer with an aperture grid available as a sequential system with rapid scanning PMT detection, a simultaneous system with a PMT array, and a combination system. Varian, Inc. makes a sequential ICP with PMT detection and a simultaneous system with CCD detection. ThermoElemental offers ICP Echelle spectrometers with CID detection and a sequential diffraction grating instmment with PMT detection. 

Spectrometer systems are now available with nitrogen purged, sealed optics for routine analysis from 120 to 800 nm. ICP systems that have this capability include instruments from Jobin Yvon, Inc. and from Spectro Analytical Instmments. There is one commercial DCP available from ThermoElemental, an Echelle spectrometer with CID detection. The ability to use lines in the vacuum UV permits the determination of the halogens and other elements whose most intense lines occur at < 160 nm. 

Figure 124 Plastic overlays for the qualitative analysis by an Echelle spectrometer (Fison Instruments)...

Stray light can be reduced and higher resolution obtained by using double monochromators. An echelle spectrometer equipped with a predisperser has been used. As the two instruments are operated in tandem, the exit slit of the predisperser is the entrance slit of the monochromator. 

As described in Chapter 2, spectral resolution determines the amount of detail that can be seen in the spectrum. If the resolution is too low, it will be impossible to distinguish between spectra of closely related compounds if the resolution is too high, noise increases without any increase in useful information. Spectral resolution is determined by the diffraction grating and by the optical design of the spectrometer. With a fixed detector size, there is a resolution beyond which not all of the Raman wavelengths fall on the detector in one exposure. Ideally, gratings should be matched specifically to each laser used. A dispersive Raman echelle spectrometer from PerkinElmer Instruments covers the spectral range 3500-230 cm with a resolution better than 4 cm . ... 

Scanning Echelle Spectrometers. Figure 10-7 is a schematic of an echelle spectrometer that can be operated either as a scanning instrument or as a simultaneous multichannel spectrometer. Scanning is accomplished b> moving a photomultiplier tube in both x and... 

A Charge-lnjectioii Device Instrumeat. A number of companies offer multichannel simultaneous spectrometers based on echelle spectrometers and two-dimensional array devices. This type of instrument has replaced other types of multichannel emission spectrometers in many applications. 

In the first step one should estimate the total amount of bandwidth increments which have to be recorded. It has been pointed out in Section 2.1.5 that for HR-CS AAS the width of the instrumental profile AAjnstr should depend on the wavelength A in a form which is well met by echelle spectrometers with ... 

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