Defense Date

8-5-2020

Graduation Date

Fall 12-18-2020

Availability

One-year Embargo

Submission Type

dissertation

Degree Name

PhD

Department

Chemistry and Biochemistry

School

Bayer School of Natural and Environmental Sciences

Committee Chair

H. M. Skip Kingston

Committee Member

Michael J. Van Stipdonk

Committee Member

Stephanie J. Wetzel

Committee Member

Marvin D. Anderson

Keywords

Hexavalent Chromium, SIDMS, IDMS, Cr(VI), Speciated, ICP-MS, 6800, 3060A, SRM

Abstract

The ability to perform accurate, repeatable, and defensible elemental and molecular speciated analysis is immensely significant for measurements that support human health, environmental science, and industry. This is especially true since trivalent chromium [Cr(III)] is necessary for proper nutrition, while hexavalent chromium [Cr(VI)] is extremely toxic, genotoxic, and carcinogenic. The main challenges associated with speciated analysis are related to reactive species that are continuously transformed or converted to other species during sample processing. Accurate determination of Cr(III) and Cr(VI) species require a method that is capable of monitoring and correcting for interconversion, bias, and instrumental error. Traditional quantitative methods, such as calibration curves, are unable to account for such species interconversion. However, Speciated Isotope Dilution Mass Spectrometry (SIDMS) chromium analysis by EPA Method 6800 and EPA Method 3060A ensures that interconversions are quantifiable. This dissertation demonstrates the certification of a new Sigma-Aldrich ambient-level Cr(VI) standard reference material in soil matrix using SIDMS methodology. Also, the concentrations and stability of Cr(VI) in a variety of dietary supplement samples by a microwave-enhanced alkaline extraction protocol integrated with SIDMS are presented along with discussion of the Eh and pH phase diagrams of chromium in dietary supplement samples. Using ion chromatography (IC) separation and inductively coupled plasma mass spectrometry (ICP-MS), isotopic ratios were measured and used to calculate initial concentrations of Cr(III) and Cr(VI) in the original unaltered samples. Challenges associated with the analytical method development are discussed along with details of the sample preparation, microwave-enhanced alkaline extraction, and quantitative data processing.

Language

English

James Henderson Dissertation 100920.docx (2133 kB)
James Henderson Dissertation 100920

Available for download on Saturday, December 18, 2021

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