Sequential spectrometers, atomic emission

Inductively-Coupled Plasma Atomic Emission Spec-trowe/er—Either a sequential or simultaneous spectrometer is suitable, if equipped with a quartz ICP torch and r-f generator to form and sustain the plasma. 

In Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), a gaseous, solid (as fine particles), or liquid (as an aerosol) sample is directed into the center of a gaseous plasma. The sample is vaporized, atomized, and partially ionized in the plasma. Atoms and ions are excited and emit light at characteristic wavelengths in the ultraviolet or visible region of the spectrum. The emission line intensities are proportional to the concentration of each element in the sample. A grating spectrometer is used for either simultaneous or sequential multielement analysis. The concentration of each element is determined from measured intensities via calibration with standards. 

The plasma is maintained at a temperature of 10 000° C by an external radio frequency current, as described in Section 3.3. At this temperature, many molecular species are broken down, and approximately 50% of the atoms are ionized. So far this is identical to ICP-OES, but for ICP-MS we are not interested in the emission of electromagnetic radiation, but rather in the creation of positive ions. To transfer a representative sample of this plasma ion population to the mass spectrometer, there is a special interface between the plasma and the mass spectrometer. This consists of two sequential cones... 

The tail of the plasma formed at the tip of the torch is the spectroscopic source, where the analyte atoms and their ions are thermally ionized and produce emission spectra. The spectra of various elements are detected either sequentially or simultaneously. The optical system of a sequential instrument consists of a single grating spectrometer with a scanning monochromator that provides the sequential detection of the emission spectra lines. Simultaneous optical systems use multichannel detectors and diode arrays that allow the monitoring of multiple emission lines. Sequential instruments have a greater wavelength selection, while simultaneous ones have a better sample throughput. The intensities of each element s characteristic spectral lines, which are proportional to the number of element s atoms, are recorded, and the concentrations are calculated with reference to a calibration standard. 

Sodium silicate is somev at more difficult to analyze than many other materials because of the formation of the relatively long lived radionuclide Na whose emissions interfere with the detection of other elements. Nevertheless we were able to determine, in a sample of sodium silicate, that many heavy elements of toxicological concern were undetectable down to the ppm to ppb level in the undiluted silicate (13), An XRF spectrometer can be configured to perform sequential multi-elemental analyses. It is less sensitive to the elements of lower atomic number. Also, since the X-rays penetrate only to a depth of about 10 urn, the sample must be homogeneous. Solid samples must be presented to the X-ray beam with a flat surface. However, the relative ease of sample preparation and the ability to run glasses and solutions with only minor dilution make X-ray fluorescence a useful technique where analysis for a wide range of impurities is required,... 

The glow discharge (GD) is a reduced-pressure gas discharge generated between two electrodes in a tube filled with an inert gas such as argon. The sputtered atom cloud in a GD source consists of excited atoms, neutral atoms, and ions. The emission spectrum can be used for emission spectrometry in the technique of GD-OES, but the GD source can also be used for AAS, AFS, and MS. The source can be used with any of the types of spectrometers discussed for plasma emission sequential monochromator, Rowland circle polychromator, echelle spectrometer, or combination sequential-simultaneous designs. The detectors used are the same as described for plasma emission spectrometry PMTs, CCDs, or CIDs. 

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