Multielement flexibility

Advanced computerisation and sensorisation and developments in the field of multielement optical detectors (CCD and PDA) and fibre optic remote spectroscopy have added modularity and flexibility. Silica-silica fibres used for spectroscopy applications are multimode with core diameters from 50 to 1000 p,m. The application of new technologies to optical instrumentation (e.g. improved gratings in spectrographs, the use of... 

Flexibility. An instrument which can analyze a sample only for a fixed combination of elements is useful for routine analyses, such as clinical analyses, but becomes useless if the combination of elements is to be varied. The ideal multielement spectroscopic system would be able to determine any combination of elements desired, if those elements are amenable to analysis by spectroscopic techniques. Since real samples contain various elements in differing relative concentrations, it is necessary that an ideal multielement spectrometer be able to accept such samples without the need for varying dilutions to accomodate all elements present. Thus the instrument should have a wide dynamic range and be capable of adjustment so that different elements present in major, minor, and trace quantities in the same sample can be simultaneously monitored. 

In a system for coherent forward scattering, the radiation of a primary source is led through the atom reservoir (a flame or a furnace), across which a magnetic field is applied. When the atom reservoir is placed between crossed polarizers scattered signals for the atomic species occur on a zero-background. When a line source such as a hollow cathode lamp or a laser is used, determinations of the respective elements can be performed. In the case of a continuous source, such as a xenon lamp, and a multichannel spectrometer simultaneous multielement determinations can also be performed. The method is known as coherent forward scattering atomic spectrometry [309, 310]. This approach has become particularly interesting since flexible multichannel diode array spectrometers have became available. 

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. 

Summarizing, the potential of ICP-MS lies in the fact that analyses can now be performed with the flexible sampling of an ICP, with true multielement capacity and a high power of detection. 

Figure 7.27 A combination sequential-simultaneous ICP emission spectrometer. Such a combination permits rapid multielement analysis using the polychromator and preselected wavelengths. The monochromator adds the flexibility to monitor additional elements or alternate wavelengths in case of spectral interferences. [Courtesy of Jobin Yvon, Inc., Horiba Group, Edison, NJ (www. jyhoriba.com).]...

The major strengths of atomic spectroscopy techniques over other methods is that they are relatively inexpensive, and they provide outstanding flexibility in terms of automation and multielement analysis capabilities (almost the whole Periodic Table). These advantages, coupled with high precision and accuracy, make atomic spectoscopy a preferred method of analysis. 

The real benefit of the universal collision/reaction cell approach is that it can be used in both the collision cell and the reaction cell modes. This means the operator has the flexibility of operating the system in three different modes all in the same multielement method—in the standard mode for elements where interferences are not present in collision mode for removal of minor interferences and in dynamic reaction mode for the most severe polyatomic spectral interferences. 

To a hmrted extent, atomic absorption spectrometry can also be used for multielement determinations. Several manufacturers introduced systems with multilamp turrets, where different lamps can be held under pre-heated conditions. Here, rapid switching from one lamp to another enables sequential multi-element determinations to be made by flame atomic absorption, for a maximum of around five elements. Simultaneous determinations are possible with multi-element lamps, however, the number of elements that can be brought together and used as a hollow cathode lamp with a sufficiently stable radiation output and lifetime is rather limited. The use of continuous sources facilitates flexible multi-element determinations for many elements in principle. It is necessary to use high-resolution spectrometers (e.g., echelle spectrometers) with multi-channel detection. CCDs of-... 

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