Date of Award

Spring 1989

Project Type

Dissertation

Program or Major

Chemistry

Degree Name

Doctor of Philosophy

Abstract

The goal of this research was to develop methods for the in-situ determination of 2,4,6-trinitrotoluene (TNT) and other polynitroaromatic compounds in groundwater. The first approach was to use an adsorbent to preconcentrate TNT for direct determination. Poly(vinyl alcohol) was crosslinked with glutaraldehyde to form a clear gel that is transparent into the ultraviolet. The volume and swelling of the gel can be controlled by varying the amount of glutaraldehyde. The coefficient for TNT partitioning between the gel and water is 1.4. The gel offers important advantages as a matrix for chemical sensor development, but is not suitable for determining TNT in groundwater because the partition coefficient is too small.

A TNT-sensitive membrane was prepared by dissolving the following in tetrahydrofuran: 0.50 g poly(vinyl chloride), 0.20 ml dioctyl phthalate, and 0.12 ml Jeffamine T-403, a polyoxyethyleneamine which reacts with TNT to produce colored products. The membrane is formed by casting the solution into a glass Petri dish with a diameter of 8.8 cm and allowing the solvent to slowly evaporate. Trace amounts of 1,3,5-trinitrobenzene, 2,4,5-trinitrotoluene, and N-picryl-methylnitramine also reacted with the membrane to produce a reddish brown color but their visible absorption spectra differ from that of TNT. Application of the membrane to groundwater sample analysis is comparable with previously developed HPLC methods. Recoveries from groundwater spiked to contain 0.1 to 4.0 ppm TNT ranged from 95% to 105%.

Single fiber optical measurement of membrane absorption was developed for remote in-situ detection of TNT. Refractive index matching to reduce stray light and a reflector behind the membrane to increase reflected intensity were essential to keep the stray light levels small relative to the signal of interest. To compensate for drift, the reflected intensity at 500 nm is measured relative to the reflected intensity at 824 nm, a wavelength where intensity is not affected by color formation in the membrane. The rate at which the ratio of reflected intensity at 824 nm to reflected intensity at 500 nm increases is a function of TNT concentration.

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