Award Date

1-1-2007

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

First Committee Member

Spencer Steinberg

Number of Pages

106

Abstract

Halide anions such as iodide have important roles in biological and environmental sciences. Environmental iodine is useful in oceanography and atmospheric studies as well as studies of soils and mineral deposits. The fission product, Iodine-129, is a major concern to the Department of Energy because it is a radiation hazard to the public. Consequently, there is great potential value in examining patterns of iodine migration and sorption near weapons test sites and nuclear waste facilities. Traditional iodide analyses, such as by ion chromatography or ion selective electrode, are generally limited to ppm concentrations. Electrochemical methods are very sensitive but vulnerable to organic fouling and interference by other ionic species. The goal of this project was to develop a sensitive iodide and iodate assay to apply to the analysis of environmental water and soil samples. Two different approaches based on GC/MS were developed and tested; The first approach is based on adsorption of the iodide in an aqueous sample by anion exchange resin. The resin is then analyzed by pyrolysis-GC/MS. Pyrolysis of the resin yields methyl iodide, a favored reaction product. During pyrolysis the methyl iodide (MeI) is produced in proportion to its abundance in the sample and can be analyzed by GC/MS. Standard concentration iodide solutions are used to produce a calibration curve. The iodide concentrations of environmental samples are quantified by correlation to the calibration curve. Two strong base anion exchange resins were studied. The first, AG1-X8, consists of poly(styrene-co-divinylbenzyltrimethylammonium chloride). A pyridine based polymer, poly(divinylbenzene-co-1-methyl-4-vinylpyridinium chloride), was the other resin studied. The two quaternary amine based resins were used to derive calibration curves and to analyze samples. Acceptable calibration curves were generated with AG-1 and the poly-pyridinium chloride resin over the iodide concentration range, 5 nanomolar to 500 nanomolar. However, the I- analyses by pyrolysis-GC/MS of environmental samples (e.g. Lake Mead water samples) proved to be unacceptable in both accuracy and precision; Efforts were redirected to the determination of iodide and iodate in environmental samples by the second assay method. Iodide in a 50.0 mL aqueous sample is derivatized to methyl iodide by reaction with dimethylsulfate in a 60 mL septum (crimp) sealed reaction vessel. After the reaction is finished a 500 muL gas sample of the reaction vessel headspace is analyzed for MeI by GC/MS. Acceptable calibration curves were obtained for the I- concentration range, 1 nanomolar to 500 nanomolar. Total inorganic iodine (TII) is quantified by reducing the sample iodate to iodide with sodium dithionite and then applying the same analytical procedure as described above for iodide. Iodate is then determined by the difference between TII and iodide. Measurements of iodide and iodate were made on Las Vegas tap water and Lake Mead water samples. In addition, the soluble iodide and iodate concentrations in salt rich soil samples from the Virgin River area (Black Butte Series) were determined.

Keywords

Analysis; Iodate; Iodide; Soil; Water

Controlled Subject

Chemistry, Analytic

File Format

pdf

File Size

2867.2 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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