Date of Award

Fall 2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry & Biochemistry

Program/Concentration

Chemistry

Committee Director

Patrick G. Hatcher

Committee Member

Paula A Mazzer

Committee Member

Bala Ramjee

Committee Member

Richard V. Gregory

Call Number for Print

Special Collections LD4331.C45 M47 2010

Abstract

Recent studies of ice cores have embarked on the task of determining the classes of dissolved organic matter (DOM) present in melt-water from the cores collected in numerous locations in the northern and southern hemispheres. This DOM originally derives from wet precipitation and is thought to reflect atmospheric organic matter derived from anthropogenic and non-anthropogenic sources. Because the amount of DOM is so low, previous studies have necessarily used large sample volumes (greater than 500 mL) to concentrate sufficient ice core DOM necessary for mass spectral analysis. Solid phase extraction (SPE) with C18 resins was followed by evaporative concentration and electrospray ionization, by direct infusion, coupled to ultrahigh resolution mass spectometers to analyze core samples. To mitigate the need for large volumes of ice core melt-water, I am here proposing to employ nanospray ionization Fourier transform ion cyclotron resonance mass spectrometry as an efficient tool for examining ice core DOM, due to the reduced sample volume needed for analysis (less than 30 μL). Using smaller sample volumes is important for resolving temporal changes in ice core DOM. I demonstrate that one can analyze less than 100 mL of ice core meltwater with sufficient mass spectral sensitivity to describe the molecular composition of the DOM. Over 1500 unique molecular formulas for two different ice core samples dated in approximate age to 1660 AD and 1360 AD were obtained from the analyses. I used the molecular formula assignments to observe changes in ice core DOM brought about by choice of SPE resin (PPL SPE vs. C18 SPE) and by natural variations due to differences in the nature of wet precipitation in ancient times of deposition (1660 AD vs. 1360 AD). Based upon the types of molecular formulas extracted from each sample, I calculated the degree of carbon oxidation inherent in the DOM and probably derived from atmospheric processing that occurred at the time of deposition. The calculated carbon oxidation number provides an evaluation of the degree of oligomerization and de-functionalization that can be associated with the DOM from the two time periods (1660 AD and 1360 AD). It is clear that the 1660 AD DOM is more oxidized than that deposited at an earlier time period.

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DOI

10.25777/r1g2-cm37

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