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United States Department of Agriculture

Agricultural Research Service

Title: Extended Calibration Ranges for Continuum Source Atomic Absorption Spectrometry with Array Detection

item Harnly, James
item Smith, Clare

Submitted to: Spectrochimica Acta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 30, 1995
Publication Date: N/A

Interpretive Summary: Atomic absorption spectrometry (AAS) with graphite furnace atomization is a powerful, commercially available analytical method for determing trace metals at very low concentrations (ng/L). It is a single element method with a limited calibration range (3 orders of magnituede) because of the limitations of the light source, 1.e. a hollow cathode lamp. In previous work, we showed that an AA instrument with a contiuum source (a 300 W Xe arc lamp) and an array detector can provide detection limits comparable to conventional AAS. In addition, the contiuum source has intensity at all wavelengths and is therfore suitable for multielement determinations. In this paper, it is shown that with a continuum source and array detection, calibration ranges up to 6 orders of magnitude in concentration can be achieved. This extended analytical range is almost double that of conventional AAS and makes mutielement determinations feasible since separate dilutions aren't necessary for the determination of each element.

Technical Abstract: Computer modeling was used to construct calibration curves and relative concentration error plots for continuum source atomic absorption spectrometry with array detection and graphite furnace atomization. Model results agreed well with those theoretically predicted and those obtained experimentally. With a wide entrance slit width (500 um), wavelength integrated absorbance (over a spectral region equivalent to 60 times the half width of the absorption profile, ~0.16 nm for Cd at 22.8 nm) providd useful calibration ranges approaching 6 orders of magnitude of concentratio using a single calibration curve. When concentration was normalized by the intrinsic mass, all elements gave the same curve shapes with the inflection point, from a slope of 1.0 to 0.5 (on a logarithmic scale), determined by the stray light. A hyperbolic function was developed which accurately fit the modeled and experimental data. With a narrow entrance slit width (25um), wavelength selected absorbances (i.e. absorbances computed for selected pixels or wavelengths were used to construct three linear calibration curves covering 6 orders of magnitude of concentration.

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