Graduate Thesis Or Dissertation
 

Design and application of a microcomputer automated multielement flame atomic fluorescence instrument

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  • An automated multielement flame atomic fluorescence (AF) spectrometer based on microcomputer control was constructed to determine four elements simultaneously. The instrument employs a multiple exit slit monochromator where the light from various exit slits is directed to a single detector with a mirrored funnel. Each element is excited to fluoresce with a single element hollow cathode lamp (HCL) and a time multiplex mode is used for pulsing the HCL's and data acquisition. A SYM-1 microcomputer is the center of the system and controls the pulsing of HCL's, sample introduction into the flame, data acquisition, and other electronic components. Values for the experimental variables such as the HCL pulse rate, peak current, and pulse width are selected at the computer's terminal. The HCL and background signals for each element are integrated for equal periods of time selected from 0.5 to 250 ms. The integrated background (lamp off) signal is subtracted from the HCL (lamp on) signal to correct for the non-lamp related portion of the signal. For most measurements, an air/H₂ flame sheathed with Ar was the atomizer. Numerous experimental variables were optimized including HCL current and fuel and oxidant flow rates. For single element flame AF under optimum conditions, the following detection limits (in ng/mL) were obtained: Au, 2.2 x 10²; Cd, 4.8; Co, 26; Cu, 3; Fe, 50; Mg, 0.8; Mn, 7; Ni, 36; Pb, 1.0 x 10³ ; Zn, 21. For multielement flame AF under compromise conditions, the following detection limits (in ng/mL) were obtained: Cd, 10; Cu, 4; Mg, 1.5 x 10²; Zn, 1.1 x 10². With a sheathed air/C₂H₂ flame in the multielement mode, the following detection limits (in ng/mL) were obtained: Cd, 7.7 x 10²; Cu, 1.3 x 10²; Mg, 18; Zn, 4.3 x 10³. The higher flame background emission noise degraded detection limits compared to the air/H₂ flame. The system was studied briefly in a nondispersive multielement AF mode with a set of filters installed directly in front of the detector window. The following detection limits (in ng/mL) were obtained under multielement flame AF conditions with an air/H₂ flame: Cu, 33; Mg, 16; Mn, 76. The relative standard deviation of measurements for single and multiple element determinations was typically 1% or better for concentrations well above the detection limit.
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