Date of Award

December 2020

Degree Type

Thesis

Degree Name

Master of Science

Department

Chemistry

First Advisor

Joseph Aldstadt

Committee Members

Mark Dietz, Arsenio Pacheco

Keywords

Analytical Chemistry, ICP-MS, SIA

Abstract

Abstract:Because of their environmental impact, the contamination and migration of heavy metals is an important field of study. In this thesis, two novel methods for measuring toxic metals over a broad concentration range in complex matrices were successfully developed and applied to authentic samples. This research focused on toxic metals in two disparate environments: industrial effluent and soil. The primary work reported in this research focused on developing a Sequential Injection Analysis (SIA) process monitor to measure metals in industrial process waste streams in near real-time. Molecular Absorption Spectroscopy was used to determine levels of Zn and several other metals. To increase throughput, the initial rate of absorbance was studied, i.e., the slope of absorbance vs time was the signal. Various time frames for the initial rate were investigated to further increase throughput and decrease reagent use and chemical waste. The sample processing time was typically 12 minutes. The concentration range studied was from 0.1 to 1.0 parts per million (mg L -1). The LOD for the SIA initial rate method was 0.1 ppm for Zn. To test the prototype monitor, industrial effluent samples from the Milwaukee area were collected from a diverse group of manufacturing operations that involved metal processing. These samples were studied for factors that would influence analyte binding including ionic strength; pH; and presence of interfering elements. Elemental analysis of the industrial samples by ICP-MS was conducted. The most common potential interferences were Fe, Ga, and Ba, with concentrations ranging from 1.68 x 103 to 2.10 x 105 ppb. The ICP-MS method showed excellent ix precision for example, the average amount of Br in one sample was found to be 1.13 x 105 ppb with a Student’s t value at the confidence interval 95% (n=3) of 2.58 x 103 ppb (0.92% relative standard deviation). The dye films used in the SIA prototype for Zn binding were based upon PAN (1- (2-Pyridylazo)-2-naphthalene). The dye films exhibited two noteworthy complications: (a) significant matrix effects were observed that caused instrumental drift resulting in irreversible alteration of the dye film’s response to Zn, and (b) the physical detachment of the dye film from the glass slides in which they were affixed. These problems emphasized the need for more robust dye films, which must be addressed in future work to ensure the most accurate outcomes. The second project in this thesis was an investigation of heavy metal deposition at a Civil War battlefield in Manassas, VA. This site is of interest because the battle resulted in heavy metal contamination over a brief period of time in a well defined area. The metals in the soil core fractions (Pb, Cu, and Hg) were extracted by applying a modified Sequential Extraction scheme followed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Sequential Extraction was performed by subjecting the fractions to an optimized Microwave-Assisted Extraction (MAE) method. Additionally, ICP-MS allowed for an examination of other metals (Mn, Fe, Co, Ni, Cu, Zn, Ga, Ba, La, Ce, Au, Hg, Pb) present in the samples. Interesting trends in the abundance and distribution of the target analytes were observed, particularly for Mn and Co. Co levels were higher than expected (4.91 x 104 ppb on average), while Mn had unexpected variability (2.94 x 105 on average x with a range of 4.71 x 105 ppb). The levels observed for Mn, Fe, Co, Ni, Cu, Zn, Ga, Ba, La, Ce, Au, Hg, and Pb ranged from 4.36 to 4.44 x 103 ppm, which is consistent with normal background levels for soils in northern Virginia.

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