Evaluation of sampling/preconcentration techniques and pyridine derivative reagents for fluorometric determination of chloroform and TCE in water Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rx913t54g

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  • A direct purge technique was developed for the determination of chloroform or trichloroethylene (TCE) in water samples. These volatile organic solvents are transferred from the water sample to a reagent where they are trapped and react to form products (Fujiwara chemistry) that are monitored fluorometrically. Chloroform in a water sample is bubbled in a sparger into the headspace or permeated into a hollow membrane of a membrane sampling device and carried directly into a reagent in a cuvette by nitrogen gas. A simple air pump can also provide the carrier gas. With this technique, carbon dioxide (CO₂) in the air and sample solution affects the reactivity of the reagent. To compensate for this effect, the base concentration of the reagent or the pH of a water sample was adjusted. Fujiwara reagents based on pyridine derivatives were tested in dimethyl sulfoxide for their reactivity to chloroform and TCE. Base and water concentrations were varied to obtained maximum response. A new reagent based on 1-(3-pyridylmethyl)urea was found to be more selective to chloroform over TCE than previously developed reagents based on pyridine and provided a detection limit for chloroform of 6.5 ng/mL. A new reagent based on isonicotinamide provided higher selectivity for TCE than chloroform and a detection limit for TCE of 26 ng/mL. These new reagents eliminate the exposure of the user to toxic organic vapor that is experienced with common pyridine reagents. A filter fluorometer was constructed from a green diode laser and other components and used for the determination of chloroform in water. The chloroform detection limit obtained with the fluorometer is comparable to that obtained with a commercial spectrofluorometer with the typical Fujiwara reagent. With the reagent based on 1-(3-pyridylmethyl)urea, the chloroform detection limit with the fluorometer is a factor of 4 better than that obtained with the commercial spectrofluormeter.
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