Date of Award

8-2000

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Abstract

Solid phase microextraction (SPME) is an effective method for concentrating organic compounds prior to analysis by a variety of detection methods, including Fourier transform infrared spectroscopy (FTIR) and gas chromatography (GC). The first part of this work focused on the selection of an infrared-compatible solid phase that would partition phenols out of aqueous solutions. The criteria we employed dictated that potential solid phases be polar yet insoluble in water, have open regions in their IR spectra between 400-1200 cm·', 3010-3095 cm·', or 3200-3650 cm·' and be less than 200 μm thick.

Infrared spectra of a variety of proprietary epoxies and adhesives revealed baseline absorbances of greater than 2.0 au in most cases. Because the relationship between analyte concentration and IR absorbance is no longer linear when the light throughput is so low, these materials were discarded. Commercially available poly(methyl methacrylate), PMMA, was too thick for SPME use but appeared to meet our other criteria, so PMMA films were manufactured in-house. Preliminary studies were conducted to determine whether PMMA would partition either polar or nonpolar analytes from water. IR spectra of PMMA film agitated in 25 ppm o-chlorophenol revealed absorbance bands that suggested analyte partitioning had occurred, but replicate tests did not yield reproducible spectra. This was most likely due to poor reproducibility in the thicknesses of the PMMA films.

In the second part of this work, distribution constants were determined for SPME using a new calibration-efficient procedure involving the successive extraction of single solutions. Classical extraction theory defines the distribution constant (l«

The distribution constants of anthracene, m-xylene, n-octane, and 1, 1,2,2- tetrachloroethane were determined using both the new successive extraction method and a previously published, conventional method. Successive extraction K«i values were 2 840 (anthracene), 1 520 (m-xylene), 6 850 (n-octane), and 559 (1,1,2,2- tetrachloroethane). Conventional K«i values for the same compounds were 2 910, 1 740, 6 150, and 725, respectively. A statistical error analysis was conducted, revealing significantly lower percent relative standard deviations (%RSD's) in the new successive extraction method than in the more conventional method, by up to two orders of magnitude. This is due to the fact that the successive extraction method eliminates the initial analyte concentration error, which is not only included but propagated in the conventional method.

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