Graduate Thesis Or Dissertation
 

Determination of trace concentrations of cobalt via lucigenin chemiluminescence

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  • The application of lucigenin chemiluminescence for the determination of trace concentrations of Co(II) is described. This method is based on the enhancing effect that Co(II) has on the reaction of lucigenin and hydrogen peroxide in a basic solution. The chemiluminescence signal from a Co(II) enhanced lucigenin reaction, which is in excess of the signal in the absence of added metal activators, is proportional to the Co(II) concentration. The instrumentation used in the study was a previously constructed chemiluminescence photometer. The photometer is the discrete sampling system type and the luminescent signal was monitored with a photomultiplier tube. Several improvements were made to the existing instrumentation in order to minimize contamination, improve the reproducibility of the chemiluminescent signals, and decrease the analysis time. The mixing order of the reagents, their concentration and volumes, and other reaction conditions were optimized. The Co calibration curve is linear from the detection limit, 15 pptr, up to 100 ppm. A comprehensive interference study of 88 species (metals, nonmetals, common anions, and complexing agents) indicated that many species enhance or inhibit the lucigenin reaction. In many samples, most of these potential interferents are not present at a large enough concentration to interfere with the determination of ppb and sub-ppb concentrations of Co(II). A solvent extraction separation procedure was developed to isolate Co from its matrix and the most troublesome interferences (Mg and Fe), and it was used in the analysis of NBS orchard leaves. The analysis of five orchard leaves samples indicated that the Co concentration was 0.12 ppm and the relative precision was 18%. Direct analysis of a spiked tap water sample showed that dilution can be used to eliminate interferences as long as the Co concentration in the sample is at least 5 ppb. The chemiluminescent reaction of lucigenin in a strongly basic solution in the absence of hydrogen peroxide was studied and various absorption, fluorescence, and chemiluminescent spectra were obtained. The reactivity of several Co(III) complexes was investigated as well as the effect of bubbling the reaction solutions with O₂, N₂, H₂, and Ar.
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Déclaration de droits
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