Last is true inside the linear range for that element

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last is true inside the linear range for that element using that slit and that analytical line. The signal is therefore a decrease in measure light: atomic absorption spec- troscopy. Acidic Content and Oxidation State of Samples and Standards The samples and standards are often prepared with duplicate acid concentrations to replicate the analyte's chemical matrix as closely as possible. In HGAAS, acid contents of samples and standards of 10% to 50% are common; this is much much higher than in normal AAS . The oxidation state of the analyte metalloid is important in HGAAS. For instance, HGAAS analysis of selenium requires the Se(IV) oxidation state (selenite). Se(VI), the more highly oxidized state of the element (selenate), responds erratically and non reproducibly in the system. Therefore, all sele- nium in Se calibration standards and Se containing samples must be in the Se(IV) form for analysis. This can be accomplished by oxidizing all Se in the sample to selenate using a strong oxidizer such as nitric acid or hydrogen peroxide (decomposing the excess oxidant) and then reducing the con- tained selenate to selenite with boiling HCl. After that reduction step, the final acid content is made up to the required content before the sample is introduced into the hydride generation module. The literature also suggests that the time from reduction to introduction into the hydride module is impor- tant: Shorter is best. Also important is the concentration of sodium borohydride and hydrochloric acid reagents feed into the hydride generation reaction vessel: optimization of this is important and may be different for different elements. Example concentrations are 0.35% NaBH4 and 50% HCl. Note that this acid content is not necessarily identical with the acid content of the samples and standards themselves. The reagent acid's content is aimed at producing a reproducible amount of hydride in the module. Double Beam Instruments The light from the HCL is split into two paths using a rotating mirror: one pathway passes through the optical cell and another around. Both beams are recombined in space so they both hit the PMT but separated in time. The beams alternate quickly back and forth along the two paths: one instant Top Front Right side Optical Cell & Burner slot Burner head Burner head Optical Cell Hydride flows in here Flame Optical cell heated by air/C 2 H 4 flame Air/C 2 H 4 flame
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the PMT beam is split by the rotating mirror and the sample beam passes through the cell and hits the PMT. The next instance, the HCL beam passes through a hole in the mirror and passes directly to the PMT without passing through the optical cell. The difference between these beams is the amount of light absorbed by atoms in the optical cell.
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  • Fall '06
  • CHASTEEN
  • Atom, Light, hydride generation, Optical Cell

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