Flame atomization assembly with expanded views of (a) the burner head showing the burner slot where the flame is located (b) the nebulizer’s impact bead and (c) the interior of the spray chamber. The flame’s thermal energy then volatilizes the particles, producing a vapor that consists of molecular species, ionic species, and free atoms. The aerosol mist is swept through the spray chamber by the combustion gases-compressed air and acetylene in this case-to the burner head where the flame’s thermal energy desolvates the aerosol mist to a dry aerosol of small, solid particulates. When the sample exits the nebulizer it strikes a glass impact bead, which converts it into a fine aerosol mist within the spray chamber. In the unit shown here, the aqueous sample is drawn into the assembly by passing a high-pressure stream of compressed air past the end of a capillary tube immersed in the sample. Shows a typical flame atomization assembly with close-up views of several key components. On the other hand, if our interest is biologically available metals, we might extract the sample under milder conditions using, for example, a dilute solution of HCl or CH 3COOH at room temperature. This destroys the sediment’s matrix and brings everything into solution. If we need to know the total amount of metal in the sediment, then we might try a microwave digestion using a mixture of concentrated acids, such as HNO 3, HCl, and HF. What reagent we choose to use to bring an analyte into solution depends on our research goals. For this reason, only the introduction of solution samples is considered in this chapter. When analyzing a lake sediment for Cu, Zn, and Fe, for example, we bring the analytes into solution as Cu 2 +, Zn 2 +, and Fe 3 + by extracting them with a suitable reagent. If the sample is a solid, then we must bring the analyte into solution before the analysis. In most cases the analyte is in solution form. There is, however, an important additional need in atomic absorption spectroscopy: we first must covert the analyte into free atoms. The sensitivity of optogalvanic detection and the excitation of most electronic levels by the discharge make these lamps attractive also for investigating weak and excited level transitions with the use of a simple experimental setup.\)Ītomic absorption spectrophotometers use the same single-beam or double-beam optics described earlier for molecular absorption spectrophotometers (see Figure 10.3.2 and Figure 10.3.3). Sub-Doppler linewidths comparable with those achieved in atomic beams have been obtained, making a properly chosen hollow-cathode lamp a convenient tool for high-resolution spectroscopic experiments, providing wavelength references for laser frequency tuning. A Doppler background that is due to velocity-changing collisions, which may severely limit the resolution, can be greatly reduced by the choice of buffer gas. Spectra with sub-Doppler resolution of Ca i transitions at 423 (resonant), 610, 612, 616, 645, 657 (intercombination), and 672 nm were obtained by optogalvanic saturation spectroscopy in lamps filled with argon (0.6 and 2.5 Torr) and krypton (0.6 Torr). We investigated the use of hollow-cathode discharges for high-resolution and high-sensitivity spectroscopy, using atomic calcium. Note: Author names will be searched in the keywords field, also, but that may find papers where the person is mentioned, rather than papers they authored.Use a comma to separate multiple people: J Smith, RL Jones, Macarthur.Use these formats for best results: Smith or J Smith.For best results, use the separate Authors field to search for author names.Use quotation marks " " around specific phrases where you want the entire phrase only.Question mark (?) - Example: "gr?y" retrieves documents containing "grey" or "gray".Asterisk ( * ) - Example: "elect*" retrieves documents containing "electron," "electronic," and "electricity".Improve efficiency in your search by using wildcards.Example: (photons AND downconversion) - pump.Example: (diode OR solid-state) AND laser.Note the Boolean sign must be in upper-case. Separate search groups with parentheses and Booleans.Keep it simple - don't use too many different parameters.
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