High resolution echelle spectrometer

Multichannel spectrometers which allow the simultaneous determination of a large number of elements, as in atomic emission spectrometry have not encountered a breakthrough in AAS yet. However, over a number of years, work with high-intensity continuous sources and high-resolution echelle spectrometers for multielement AAS determinations has aroused some interest [160]. Fourier transform spectrometry and multichannel detection with photodiode arrays has opened new perspectives for the simultaneous detection of... 

The Hubble Space Telescope (HST) [6.206], which is the largest space-borne astronomical facility so far, was launched in 1990. The high-resolution echelle spectrometer on board the HST has provided VUV spectra, e.g. of chemically peculiar stars. Such spectra have shown an over-abundance of rare-earth elements, gold, etc. in these stars by a factor of 10 —10, relative... 

As an example of the validity of the above-mentioned description of the different broadening mechanisms. Figures 2.6, 2.7, and 2.8 show a comparison of calculated and measured line profiles as can be expected in a normal air / acetylene flame. In a first step the Cu doublet at 324.754 nm was measured with the high-resolution echelle spectrometer... 

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. 

Echelle spectrometers can also be made small, when only part of the spectrum is to be used, while still having a considerably high spectral resolution. In Echelle systems, dedicated parts of the spectrum are often measured with a separate built-in spectrometer. This is e.g. the case in ICP-OES for the spectral range where the most sensitive alkali lines are found [345],... 

The detection limits for most elements are of the order of 5-100 ng/mL. For elements with very sensitive atomic lines such as As, B and P, the detection limits are slightly lower than in ICP-AES [371]. The high level of detection is also certainly related to the high resolution of the Echelle spectrometer used. Different concentrations of alkali elements, however, cause higher matrix effects than in ICP-AES and may even necessitate the use of spectrochemical buffers. The analytical precision achievable is high and RSDs below 1% can be reached. The system can cope with high salt contents (>100 g/L) and has found considerable use e.g. for water analysis [372], and especially for the analysis of seawater, brines and even oils. 

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. 

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 . ... 

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