Atomic Absorption Spectrometry (AAS) Systems and Technologies
The standard AAS instrument consists of four components: the sample introduction area, the light (radiation) source, the monochromator or polychromator, and the detector (figure 1).
Following absorption, the characteristic wavelengths emitted from the excitation sources, the flame or graphite furnace, are transferred and focused into the optic system of the AAS. Because any decrease in the light intensity of a given wavelength is proportional to the concentration of the analyte in the sample, this value can be used for quantification of the analyzed elements.
The following systems and technologies greatly simplify both FAAS and GFAAS technologies.
Autodilutor system—An automated in-line dilutor and standards preparation system for flame atomic absorption spectrometry (FAAS).
Solution-based spectrometric elemental analysis techniques require the preparation of standard solutions to calibrate the spectrometer for each analysis. In FAAS, at least three calibration standards are needed to accurately track the calibration graph curvature. Preparation of these calibration standards is one of the more time-consuming processes of most analytical laboratories. Standards preparation frequently involves multiple dilution steps, increasing the risk of contamination and operator errors. A consequence of FAAS calibration curvature is that the dynamic concentration range of the instrument is relatively short, so real sample concentrations may lie above the top standard and linear region of a calibration. The user then has to pause the analysis and dilute the samples that are over the limit until they lie within the calibrated range.
Autodilutor systems are designed to take over these labor-intensive tasks by automatically preparing working calibration standards from a single master standard. In this way, no manual dilution steps are required. Autodilutor systems also simplify the task of handling samples found over the limit by diluting them into the calibration range.
Continuous flow vapor generation system—A powerful tool used for the measurement of hydride-forming elements.
Hydride generation AAS employs a chemical reaction to create volatile metal-hydride species that can be analyzed in the vapor phase. Suitable liquid reagents are mixed with samples in a reaction zone to form the hydride vapor. This vapor is then separated from the liquid mixture in a gas-liquid separator and carried to an atomization cell that can be heated (if required). When heated, the hydride decomposes and releases atoms, which are then measured by atomic absorption. The cell can be heated using the air-acetylene flame or an electrically heated furnace.
For mercury analysis, no heating is required because the chemicals form elemental mercury, which passes as a vapor into the atomization cell.
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